Hydraulic Control System

Field

The present invention relates to a hydraulic control system, in particular, to a hydraulic demultiplexer or multiplexer.

Background

The use of fluids in control logic systems is known, including from before the advent of the transistor and before the scaling of microelectronics. In addition, it is known to implement fluidic logic in pneumatic devices. For example, US 10,322,411 relates to the implementation of fluidic logic in a pneumatic microfluidic device. Furthermore, “Soft Robots for Extreme Environments: Removing Electronic Control” by Mahon et al. describes a soft robot system controlled using pneumatic control lines.

In certain environments and for certain applications, a hydraulic system may be preferable to a pneumatic system, for example, in a robotic system where a high level of power may be required. A typical hydraulic system may have a large number of actuators that need to be individually addressed to control operation of the system. For example, a known hydraulic system may have over 50 actuators that need addressed to provide control.

A known method of addressing actuators in a hydraulic system is to use an electrohydraulic controller in which each actuator of the system is coupled to a correspond valve. The valve is energized using an electronic control signal from an electronic controlled thereby providing electronic control of the actuators. However, in certain environments, electronically controlled robotics are unsuitable e.g. due to spark risk, presence of strong radiation sources, risk of failure in a hazardous environment. Therefore, there is a need for electronic-free control systems capable of operating complex, hydraulic equipment to undertake complex tasks.

In environments in which electronic control systems are not suitable, it is known to use hydraulic activated pilot valves in which a hydraulic control signal energises a spool into position in a valve. Each actuator requires a single controlled valve and therefore when the number of actuators becomes large the complexity scales. Therefore, known fluid logic and known hydraulic systems may be unsuitable for the complexity required to create the stacked logic capable of operating robotics. Summary

In accordance with a first aspect, there is provided a hydraulic demultiplexer or multiplexer for providing hydraulic actuation of a plurality of robotic components wherein the hydraulic demultiplexer or multiplexer comprises: an arrangement of hydraulically- controlled and/or hydraulically operated valves.

Hydraulic control may comprise changing a state of a valve using a hydraulic fluid and/or a change in hydraulic pressure. Hydraulic operation may comprise causing a movement of a moveable valve element using a hydraulic fluid and/or a change in hydraulic pressure.

A hydraulically controlled valve may be in one or more states. A hydraulically controlled valve may be such that the state of the hydraulically controlled valve is changed from a first state to a second state using one or more hydraulic fluids. A hydraulically controlled valve may be such that a change of state of the valve is caused by a change in hydraulic pressure. A hydraulically operated valve may comprise a moveable element. The hydraulically operated valve may be such that the action of one or more hydraulic fluids on the moveable element causes movement of the moveable element. Movement of the moveable element of the hydraulically operated valve may be caused by the action of a change in hydraulic pressure on the moveable element.

The hydraulically-controlled valves may provide hydraulic control. The hydraulically- operated valves may provide hydraulic power. The valves may comprise valves that are both hydraulically controlled and hydraulically powered. The valves may comprise hydraulic valves that provide hydraulic control of a first hydraulic fluid using a second hydraulic fluid.

The hydraulic demultiplexer or multiplexer may be a hydraulic demultiplexer. The hydraulic demultiplexer or multiplexer may be a hydraulic multiplexer.

The arrangement of valves may form part of a hydraulic routing circuit between a common fluidic input and one or more fluidic outputs. The arrangement of valves may be controllable using one or more hydraulic fluidic control signals thereby to place one of the one or more hydraulic fluidic outputs into fluid communication with the common fluidic input. The one or more hydraulic fluidic outputs may comprise a plurality of hydraulic fluidic outputs.

The number of fluidic outputs may be any suitable number of outputs and may be dependent on the application. The common fluidic input may comprise a hydraulic input line and/or an input port suitable for receiving a hydraulic fluid. Each fluidic output may comprise a hydraulic output line and/or an output port suitable for outputting a hydraulic fluid. The number of fluidic outputs may be in the range 1 to 10,000. The number of fluidic outputs may be in the range 1 to 1000. The number of fluidic outputs may be in the range 1 to 100. The number of fluidic outputs may be in the range 1 to 10.

The arrangement of valves may be configured to be moved between a plurality of configurations, using a hydraulic fluid, such that in each configuration a fluidic route from the common fluidic input to one of the one or more fluidic outputs is provided. The arrangement of valves may be hydraulically controllable to selectively switch between the configurations of valves in response to receiving one or more hydraulic fluid control signals.

The hydraulic demultiplexer or hydraulic multiplexer may be operable as a demultiplexer or as a multiplexer. When operated as a multiplexer, the common fluidic input may be referred to as a common fluidic output and the one or more fluidic outputs may be referred to as one or more fluidic inputs. The hydraulic demultiplexer or multiplexer may comprise hydraulic hosing and lines for coupling the arrangement of valves. The hydraulic demultiplexer may comprise the plurality of actuators for actuating the robotic components.

The arrangement of valves may comprise hydraulically-controlled valves configured to be controlled using a first hydraulic fluid thereby to control movement of a second hydraulic fluid. The first hydraulic fluid may be at a first pressure and the second hydraulic fluid at a second, higher pressure. The pressure of the second hydraulic fluid may be suitable for actuating the plurality of robotic components.

The first hydraulic fluid may be in a pressure range between 50 and 10,000 psi, optionally in the range 50 to 1000 psi, optionally in the range 600 to 800 psi. The second hydraulic fluid may be in a pressure range between 0 and 10,000 psi, optionally in the range 50 to 1000 psi, optionally in the range 600 to 800 psi. The operating pressure of the hydraulic fluid(s) may be dependent on the application of the demultiplexer or multiplexer.

The arrangement of valves may comprise a plurality of fluidic logic modules, wherein each fluidic logic module comprises one or more valves configured to receive one or more hydraulic fluids and configured to output a hydraulic fluid in accordance with a logical operation.

Each fluidic logic module may comprise one or more valves configured to receive one or more hydraulic fluids and configured to output a hydraulic fluid in accordance with a logical operation comprising one or more of: AND, NOT, OR, NAND, NOR, XOR, XNOR.

Each fluidic logic module may operate in accordance with a logical operation selected from a functionally complete set. The functionally complete set may be one of the following minimal functionally complete sets: {AND, NOT} or {OR, NOT} or {NAND} or {NOR}. The functionally complete set may be a set formed using two or more of the minimal functionally complete sets.

The arrangement of valves may comprise: a differential valve configured to receive a first hydraulic fluid at a first pressure and a second hydraulic fluid at a second pressure and configured to selectively output a hydraulic fluid dependent on the pressure in dependence on the first pressure and the second pressure.

The differential valve may be configured to output a fluid when at least one of the first pressure and the second pressure is substantially non-zero or above a threshold value.

The threshold value may be dependent on one or more physical parameters of the differential valve. The differential valve may be designed by selecting one or more of the physical parameters of the differential valve dependent on a desired operating pressure or vice versa. The differential valve may comprise a shuttle valve.

The threshold value may depend on, for example, the size and mass of the shuttle of the shuttle valve. The differential valve may be configured to selectively output either: the first hydraulic fluid, the second hydraulic fluid or no hydraulic fluid. The differential valve may be configured to output the first hydraulic fluid when the second pressure is substantially zero and output the second hydraulic fluid when the first pressure is substantially zero.

The differential valve may comprise: a first inlet for receiving the first hydraulic fluid; a second inlet for receiving the second hydraulic fluid; an outlet for outputting the first hydraulic fluid and/or the second hydraulic fluid; a moveable valve element provided in a valve chamber, wherein the moveable valve element is configured to be moved in the valve chamber in dependence on the difference in the first pressure and the second pressure thereby to place the differential valve in one of: a first open configuration, a second open configuration and a closed configuration.

When the differential valve is placed in the first open configuration a first fluidic path may be provided between the first inlet and the outlet. When the differential valve is provided in the second open configuration a second fluidic path may be provided between the second inlet and the outlet. When the differential valve is provided in the third open configuration both a first fluidic path may be provided between the first inlet and the outlet and a second fluidic path may be provided between the second inlet and the outlet.

The one or more physical parameters of the differential valve on which the threshold value depends may include, for example, at least one of: the size and/or dimensions of the first inlet and/or the second inlet; the size/dimensions/mass of the moveable element; the size/dimensions of the valve chamber.

The arrangement of valves may comprise an inverter valve configured to receive a hydraulic fluid at a first pressure and output a hydraulic fluid when the first pressure is equal to or above a threshold value.

The inverter valve may comprise a normally open spring return pilot valve The inverter valve may comprises a control inlet, a supply inlet and an outlet. The inverter valve may be configured to be moved between an open configuration and a closed configuration based on the pressure of hydraulic fluid received at the control inlet, such that, when in the open configuration a fluidic path is provided between the supply inlet and the outlet and, when in the closed configuration, no fluidic path is provided between the supply inlet and the outlet. The inverter valve may comprise a resilient member, for example, a spring element, provided in a valve chamber that is biased against the input hydraulic fluid such when the force from the input hydraulic fluid is greater than the spring force of the resilient member, a fluidic path is provided between the supply inlet and the outlet.

The arrangement of valves may comprise one or more valves arranged to receive a first hydraulic input at a first pressure and a second hydraulic input at a second pressure, wherein the one or more valves are configured to output a hydraulic fluid only when both the first pressure and second pressure are substantially zero or substantially below a threshold value.

The one or more valves may comprise a differential valve coupled to an inverter valve.

The arrangement of valves may comprise one or more valves arranged to receive a first hydraulic fluid at a first pressure and a second hydraulic fluid at a second pressure, wherein the one or more valves are configured to permit fluid flow of a further received hydraulic fluid only when at least one of the first pressure and the second pressure is substantially zero or below a pre-determined threshold and configured to not permit fluid flow of the further received hydraulic fluid only when both the first pressure and second pressure are substantially non-zero or above the pre-determined threshold.

The arrangement of valves may be configured to use hydraulic fluid having a hydraulic pressure in the range 50 to 10,000 psi, optionally in the range 50 to 1000 psi, optionally in the range 600 to 800 psi.

The demultiplexer or multiplexer may be configured so that equal fluid resistances are provided at each valve of the arrangement of valves. The equal fluid resistances may be provided at each valve of the arrangement of valves by providing at least one of pressure relief valves in the hydraulic demultiplexer or multiplexer and selecting one or more dimensions of the hydraulic lines, for example, by balancing the hydraulic lines by length and diameter.

In accordance with a second aspect, there may be provided a hydraulic system comprising a hydraulic demultiplexer or multiplexer, for example, the hydraulic demultiplexer or multiplexer of the first aspect. The system may comprise a controllable switch for controlling the arrangement of valves using a hydraulic fluid. The switch may be controllable using timing signals.

The system may be suitable for use in severe environments and/or for robotics. The system may further comprise the plurality of actuators, optionally the plurality of robotic components. The system may further comprise hydraulic hosing and lines for coupling the arrangement of valves with the plurality of actuators. The system may comprise at least one hydraulic fluid supply, for example, a pump. The system may comprise at least one control fluid supply. The system may comprise at least one hydraulic fluid return, for example, a tank.

The controllable switch may be an electronic switch and be configured to control the flow of hydraulic fluid to the demultiplexer or multiplexer. The electronic switch may be configured to control the flow of a supply fluid and control fluids to the demultiplexer or multiplexer. The electronic switch may be configured to separately turn each of the supply fluid and control fluids on and off. The controllable switch may be provided remotely from the demultiplexer.

In accordance with a third aspect, there is provided a hydraulic valve configured to receive a first hydraulic fluid at a first pressure and a second hydraulic fluid at a second pressure, wherein the valve is configured to permit flow of a further received hydraulic fluid only when at least one of the first pressure and the second pressure is substantially zero or below a pre-determined threshold and to prevent flow of the further received hydraulic fluid though the valve when both the first pressure and second pressure are substantially non-zero or above a pre-determined threshold.

The hydraulic valve may be for use in a hydraulic demultiplexer or multiplexer. The valve may comprise a moveable member moveable in a valve chamber, wherein the moveable member is configured to be moved by the first and/or second received hydraulic fluids to provide a permitted fluidic path through the valve for the further received hydraulic fluid, wherein the moveable member is shaped to form part of the permitted fluidic path.

The hydraulic valve may comprise a first inlet for receiving the first hydraulic fluid and a second inlet for receiving the second hydraulic fluid. The moveable element may be provided in a chamber. The moveable element may be moveable in the chamber in response to receiving the first or second hydraulic fluids to place the valve in one or more open configurations or a closed configuration. The valve may be placed in the open configuration when the pressure of both the first hydraulic fluid and the second hydraulic fluid are substantially non-zero or above a pre-determined threshold. When in the closed configuration, a fluidic path through the valve is blocked by the moveable element. The valve may further comprises a supply inlet and an outlet. In the first open configuration, a first fluidic path may be provided between the supply inlet and the outlet and in the second open configuration, a second fluidic path is provided between the supply inlet and supply outlet. In the closed configuration, no fluidic path may be provided between the supply inlet and outlet.

The pre-determined threshold is dependent on the one or more properties of the moveable element. The moveable element may be coupled to a spring element, or other resilient means, and the pre-determined threshold dependent on the stiffness and/or spring constant of the spring element.

The moveable member and valve chamber may be shaped to define three cavities that are sealed from each other.

The three independent cavities may comprise a first cavity for the first received hydraulic fluid and a second cavity for the second received hydraulic fluid and a third cavity for the further received hydraulic fluid. The cavities are sealed such that fluid flow is prevented from passing between the cavities. The moveable element may be moveable, in response to the first and/or second received hydraulic fluid, between three positions. The moveable element may comprise a first groove and a second groove, such that, when in a first position in the valve, the first groove provides part of a first permitted fluidic path for the further received hydraulic fluid through the valve and when in a second position in the valve, the second groove provides part of a second permitted fluidic path for the further received hydraulic fluid, wherein the moveable element is moveable between the first and second position by the first and/or second received hydraulic fluids.

The movement of the moveable member may be in response to receiving the first hydraulic fluid and/or the second hydraulic fluid is substantially perpendicular to the permitted flow of hydraulic fluid through the valve. The moveable member may be substantially unmoved in the chamber by the permitted fluid flow. The moveable member may be coupled to a spring element and biased such that, in its natural state, the valve is in a first open configuration and moveable in response to receiving an input hydraulic fluid. The moveable member may be such that, in response to receiving equal forces at either side the moveable element is moveable to place the valve in a closed configuration.

In accordance with a fourth aspect, there is provided a hydraulic demultiplexer for providing hydraulic actuation of a plurality of robotic components wherein the hydraulic demultiplexer comprising an arrangement of hydraulically-controlled and hydraulically- operated valves.

In accordance with a fifth aspect, there is provided a hydraulic multiplexer for providing hydraulic actuation of a plurality of robotic components wherein the hydraulic multiplexer comprises an arrangement of hydraulically-controlled and hydraulically-operated valves.

In accordance with a sixth aspect, there is provided a method of providing hydraulic actuation of a plurality of robotic components comprising providing a hydraulic demultiplexer or multiplexer coupled to the plurality of robotic components, wherein the hydraulic demultiplexer or multiplexer comprises an arrangement of hydraulically- controlled and hydraulically-operated valves and actuating the plurality of robotic components by providing one or more hydraulic fluids to the arrangement of hydraulically-controlled and hydraulically-operated valves. Features in one aspect may be applied as features in any other aspect, in any appropriate combination. For example, hydraulic demultiplexer or multiplexer features may be applied as hydraulic system features and vice versa. As a further example, hydraulic valve features may be applied as hydraulic demultiplexer or multiplexer or hydraulic system features and vice versa. As a further example, demultiplexer or multiplexer, system or valve features may be applied as method features and vice versa.

Brief Description of Drawings

Various aspects of the invention will now be described by way of example only, and with reference to the accompanying drawings, of which:

Figure 1 is a schematic overview of a demultiplexer;

Figure 2 is a schematic overview of the demultiplexer, in operation;

Figures 3(a) and 3(b) are schematic diagrams of two representations of a demultiplexer using logical operations;

Figure 4 is a schematic diagram of a hydraulic demultiplexer having an arrangement of hydraulic valves, in accordance with an embodiment;

Figure 5 illustrates a first hydraulic valve for use in a hydraulic demultiplexer;

Figure 6 illustrates a second hydraulic valve for use in a hydraulic demultiplexer;

Figure 7 illustrates the first hydraulic valve coupled to the second hydraulic valve to form a logical hydraulic module;

Figure 8 is a schematic overview of a demultiplexer and a further representation of the demultiplexer using symbols representing logical operations;

Figure 9 is a schematic diagram of a third hydraulic valve for use in a hydraulic demultiplexer;

Figure 10 is a schematic diagram of two instances of the third hydraulic valve coupled together;

Figure 11 is a three dimensional graphical representation of the third hydraulic valve, in accordance with an embodiment;

Figure 12 is a three dimensional graphical representation of the third hydraulic valve, in accordance with a further embodiment, and

Figure 13 is an image of the third hydraulic valve, in accordance with a further embodiment.

Detailed Description of the Drawings In the following, a hydraulic demultiplexer (also referred to as DEMUX) is described. The hydraulic demultiplexer is implemented using hydraulic components, in particular, hydraulic valves that are configured or arranged to operate in accordance with logical operations. The hydraulic demultiplexer described in the following is provided as part of a hydraulic control system that may be suitable for use in extreme environments where microelectronic systems may not be suitable. The hydraulic demultiplexer is provided to control hydraulic actuation of a number of robotic components, actuators or other hydraulic components. In the following, hydraulic demultiplexer and corresponding hydraulic multiplexers are described. A hydraulic demultiplexer (and a hydraulic multiplexer) may also be referred to as a hydraulic router or a hydraulic routing apparatus.

It will be understood that an electronic demultiplexer is a device that takes a single digital input line and routes the input line to one of a number of digital output lines. The electronic demultiplexer is controlled by one or more digital select lines (which may also be referred to as electronic control signals). A route between the input and the output can be selected based on the received select lines. For a demultiplexer having 2 ⁿ outputs, n select lines, are provided to select the output. Likewise, it will be understood that an electronic multiplexer (MUX) is a device that takes several digital input lines and selectively routes these input lines to a single output line. A multiplexer having n select lines has 2 ⁿ inputs.

The hydraulic demultiplexer described in the following operates in an analogous fashion to the electronic demultiplexer. The digital input line is replaced by a hydraulic input fluid provided to an input of the hydraulic system (an input port or input line). A number of hydraulic fluid outputs are in fluid communication with the input via an arrangement of valves. The valves are controllable using hydraulic fluid (referred to as hydraulic control signals) provided via hydraulic select lines. The valves are controllable using the hydraulic control signals to route the hydraulic fluid input to one of the outputs.

A typical hydraulic system may have a large number of actuators that need to be individually addressed to control operation of the system such that for n actuators, n hydraulic control lines are required. By providing a hydraulic demultiplexer, the number of control lines required is reduced. A hydraulic demultiplexer can have 2 ⁿ outputs from n select lines. Therefore, as an example, up to 64 hydraulic actuators can be addressed by using only six hydraulic select lines. The complexity of the control system is therefore reduced.

A number of advantages are associated with the embodiments described in the following. By using hydraulic fluid rather than using a pneumatic based system, non-linearities in the system do not need to be accounted for (as hydraulic fluid is incompressible). In addition, when pneumatic systems fail, they may expel compressed gas in a catastrophic event, which is undesirable in extreme environments. In addition, off the shelf hydraulic actuators may be used in some embodiments, therefore, these embodiments may be retrofitted to existing hydraulic machinery. In addition, hydraulic machinery has a very high power-to-weight ratio and absolute powers that far exceed electromagnetic/pneumatic systems.

The hydraulic demultiplexer described in the following may be used in a number of different environmental conditions, for example, environments where electrical control is undesirable, to provide hydraulic control and power. As a first non-limiting example, the hydraulic demultiplexer may be used in a medical environment to control and power a medical apparatus. As a further non-limiting example, the hydraulic demultiplexer may be used in hazardous environment, where electronics are undesirable.

Figures 1, 2 and 3 illustrate the concept of a demultiplexer. Figure 1(a) depicts a schematic overview of the demultiplexing operation taken from electronics. The select lines are indicated by the hatched line with the number of indicated bits for addressing the outputs (in this case, the demultiplexer is a 1 :4 demultiplexer with 2 select lines). Figure 1(a) shows the abstracted symbol for a demultiplexer and it will be understood that the input F is directed to one of the outputs A, B, C or D. For a hydraulic demultiplexer, it will be understood that the input F is a hydraulic fluid and the control signals provided via the 2 select lines are also hydraulic fluids. A schematic diagram of a hydraulic demultiplexer is described with reference to Figure 4.

Figure 2 (b) illustrates the basic operation of the demultiplexer. The four outputs A, B, C and D are connected to switches that direct the common input to the directed output. The select lines allow the switch to that output to be turned on and off such that only one output can be selected at a time. The select lines (a and b) address the outputs thus effectively switching the outputs. Figure 2 depicts in further detail, an example of binary addressing for the four-output demultiplexer of Figure 1. The two select lines are digital (i.e. take a value of 0 or 1). For any value of select line, if no input (F=0) is provided to the demultiplexer then no output is provided. For the purposes of the following description, it is assumed that there is an input (F=1).

In Figure 2(a) the select lines have a first set of values (a=0, b=0) which correspond to routing the input F to a first output (output A). In Figure 2(b) the select lines have a second set of values (a=0, b=1) which correspond to routing the input F to a second output (output B). In Figure 2(c) the select lines have a third set of values (a=1, b=0) which correspond to routing the input F to a third output (output C). In Figure 2(d) the select lines have a fourth set of values (a=1,b=1) which correspond to routing the input F to a fourth output (output D). The logical operation of the demultiplexer can be represented as a truth table, as follows:

F b a Output

Table 1 : 4:1 Demultiplexer

A demultiplexer may be built up using logical components. Figures 3(a) and 3(b) are schematic diagram showing logical circuits for a demultiplexer. Figures 3(a) and 3(b) correspond to two implementations of a demultiplexer that operate in accordance with the truth table in Table 1.

Figure 3(a) depicts an implementation of a 4:1 demultiplexer comprising only logical components from the set of {AND, NOT} logical components. Figure 3(b) depicts an implementation of a 4:1 demultiplexer using logical components from the set of {NOT, OR, NOR}. It will be understood that a demultiplexer may be implemented using only logical components selected from a single functionally complete set of logical components. Examples of minimal functionally complete sets include: {AND, NOT}, {OR, NOT}, {NAND} and {NOR}. The functionally complete set may be a set formed using two or more of these minimal functionally complete sets.

For an electronic demultiplexer, the logical components correspond to electronic components. A hydraulic demultiplexer can be implemented using hydraulics by using an arrangement of hydraulic valves that are arranged to function in accordance with logical operations. Examples of hydraulic valves that operation in accordance with logical operations are described with reference to Figures 5 to 13. In particular, while some of these are known hydraulic valves, a further valve design is described with reference to Figures 9 to 13. The representations of Figure 3 may therefore be used as implementations of a hydraulic demultiplexer, as described in the following.

A schematic diagram of an embodiment of a hydraulic demultiplexer 100 is provided in Figure 4. The hydraulic demultiplexer is a four input and one output demultiplexer. While the demultiplexer comprises an arrangement of hydraulic valves, the functionality of the demultiplexer depicted in Figure 4 is equivalent to that described with reference to Figures 1 to 3, i.e. operates in accordance with Table 1. In particular, Figure 4 is the hydraulic implementation of the logical diagram of Figure 3(b). Hydraulic components that are suitable to be used in this embodiment are described in further detail with reference to Figure 5 to 7. In the present embodiment, the arrangement of valves comprises an arrangement of hydraulically controlled and hydraulically-operated valves. As depicted in Figure 4, the arrangement of valves form part of a hydraulic routing circuit between a common fluidic input and fluidic outputs

The system 100 has a single hydraulic input line 102 (denoted by F) for receiving a hydraulic fluid input. The system also has two hydraulic select lines for conveying hydraulic control signals in the form of hydraulic fluid to the valves of the demultiplexer: a first hydraulic select line 104 (denoted by a) and second hydraulic select line 106 (denoted by b). The system has four hydraulic outputs: first hydraulic output line 108 (denoted by A), second hydraulic output line 110 (denoted by B), third hydraulic output line 112 (denoted by C) and fourth hydraulic output line 114 (denoted by D). In this embodiment, each output line is connected to a corresponding hydraulic ram. In the following, the term hydraulic control signal is used and it will be understood that the hydraulic controls signals comprise hydraulic fluid and are not electronic control signals. The four output lines (A, B, C and D) are connected to the pilot input of the valves and each valve is connected to an individual ram.

The system 100 also has a pump 120 and a tank 122. The pump 120 provides hydraulic fluid to the demultiplexer. The tank 122 collects hydraulic fluid from the demultiplexer. The fluid collected by the tank 122 is recirculated through the demultiplexer through the pump 120. While a pump and a tank are described in the present embodiment, it will be understood that the pump is a non-limiting example a hydraulic fluid supply apparatus and the tank is a non-limiting example of a fluid return or sink apparatus. While each output line is hydraulically connect to a ram in this embodiment, it will be understood that the output lines may be connected to other types of hydraulic actuators.

The arrangement of hydraulic valves operate in accordance with the logic table of Table 1 (with input F, select lines a, b and outputs A, B, C, D). In particular, the arrangement of valves is operable to be placed in a number of different configurations by providing different combinations of hydraulic control signals (in the form of hydraulic fluid) to the first hydraulic select line 104 and to the second hydraulic select line 106. In particular, the hydraulic control signals place the arrangement of valves into one of four configurations and each of the four configurations corresponds to a route from the hydraulic input line 102 to one of the output lines 108, 110, 112, 114 respectively. The different configurations correspond to different combinations of states for each valve (i.e. the valves may be open or closed).

In further detail: when no hydraulic control signals (i.e. no hydraulic fluid) are provided to either the first select line 104 or the second select line 106, the arrangement of valves is in a first configuration in which a fluidic route from the hydraulic input line 102 to the first output line 108 is provided. Likewise, providing a hydraulic control signal to the first select line 104 only (and no corresponding hydraulic control signal to the second select line 106) places the arrangement of valves into a second configuration in which a fluidic route from the hydraulic input line 102 to the second output line 110 is provided. Providing a hydraulic control signal to the second select line 106 only (and no corresponding hydraulic control signal to the first select line 104) places the arrangement of valves into a third configuration in which a fluidic route from the hydraulic input line 102 to the third output line 112 is provided. Providing a hydraulic control signal to both the first select line 104 and the second select line 106 places the arrangement of valves into a fourth configuration in which a fluidic route from the hydraulic input line 102 to the fourth output line 114 is provided.

In use, hydraulic control signals in the form of hydraulic fluid are provided to the first select line 104 and/or the second select line 106 to place the arrangement of valves in one of four different configurations thus selecting different routes from the inlet line 102 to the outlet lines 108, 110, 112 and 114. By providing hydraulic control signals to the demultiplexer, different outputs can therefore be selected allowing actuation of the hydraulic components that are in fluid communication with each of the outputs.

For example, in use, to provide a fluid to the second outlet line 110, thus actuating the coupled ram, a first hydraulic control signal is provided to the first select line 104 only thus placing the arrangement of valves into the second configuration and selecting the route between the input 102 and the second outlet line 110. For brevity placement of the valves into the other three configurations is not described here.

In this embodiment, two different pressures are present in the hydraulic system and in the hydraulic demultiplexer. The hydraulic fluid provided via the input line that is routed to the output lines and thus used to hydraulic operate the rams is separate from the hydraulic fluid used for control (i.e. the hydraulic fluid provided to select lines). The hydraulic fluid used for hydraulically operating the actuators is a higher pressure than the hydraulic pressure used for hydraulic control. The maximum operating pressure of the system is dependent on the hydraulic components used. The present embodiment, had a maximum operating pressure of 350 bar (5076.32 psi) however the pump used was limited to operating with a maximum pressure of 10 bar (145.039 psi). However, it will be understood that these values are non-limiting examples, and the maximum pressure possible in a hydraulic system may be higher that this depending on the components used.

It will be understood that Figure 4 depicts an embodiment of a hydraulic demultiplexer comprising a particular arrangement of valves in a hydraulic circuit and that the hydraulic demutliplexer may be implemented using a different arrangement of valves (other example arrangements are represented for example, in Figure 3 and Figure 8.). It will be understood that the hydraulic demultiplexer is a scalable device and while these Figures depict two select lines allowing routing from an input to four different outputs, other arrangements can be formed. For example, three select lines would allow routing from the input to eight different outputs. In general, n select lines allow routing from a single input to 2 ⁿ different outputs.

In this embodiment, it will be understood that the hydraulic demultiplexer is provided as part of a hydraulic system and that the single hydraulic input line 102, the first hydraulic select line 104 and the second hydraulic select line 106 form part of the hydraulic system and provide hydraulic inputs (supply and control, respectively) to the hydraulic demultiplexer. It will be understood that the hydraulic demultiplexer is used to control the hydraulic rams (actuators) connected to the output lines 108, 110, 112, and 114 of the hydraulic demultiplexer. In some embodiments, the actuators form part of the demultiplexer.

In some embodiments, a controllable switch is provided for controlling the hydraulic control signals (i.e. turning the hydraulic select lines one and off) and for controlling the hydraulic input. In some embodiments, the controllable switch is a mechanical switch or other suitable switch that does not use electronics.

In other embodiments, the controllable switch may be an electromechanical switch provided remotely from the demultiplexer that is controllable, using electronic signals, to turn the hydraulic select lines on and off and, in addition, the pump 120 on and off (for example, the motor for the pump, for instance, may use a relay to energize the internal solenoid for the fluid to flow). The electronic signals may be timing signals. As depicted in Figure 4, the hydraulic demultiplexer also has hydraulic hosing and lines for coupling the hydraulic components (and, for example, for coupling the demultiplexer to a reservoir/input/select lines).

It will be understood that the electronics are provided remotely from the demultiplexer. In particular, with reference to the embodiment of Figure 4, the electronic signals are used to turn the select lines 104, 106 on or off and the fluid supply 120 on or off. Figure 4 depicts a boundary 130, outside of which any electronic components are provided. In particular, the electronic signals are considered for controlling the inputs the demultiplexer rather than to control the valves of the demultiplexer or the hydraulic components controlled by the demultiplexer.

The distance between the demultiplexer and the electronics will be dependent on the application and may be a short or large distance, as desired. As a non-limiting example, in medical application, this distance may be in the range 1 to 10 metres. As a further non-limiting example, for large hydraulic systems, this distance may be in the range 10m to 1km or more. This distance may be limited by the hydraulic components used and other operational parameters, for example, the hydraulic power of the system.

In some embodiments, the control fluid could be provided by some other fluidic logic device. For example, the valves at 104 and 106 may be replaced by a solenoid valve controlled by a programmable logic controller.

As described with reference to Figure 4, known hydraulic components may be used to build a hydraulic demultiplexer. Figures 5(a), 5(b) and 5(c) depict a first suitable valve: a shuttle vale for use in the hydraulic demultiplexer. Figure 5(a) is a schematic representation of the shuttle valve; Figure 5(b) is a hydraulic circuit symbol for the shuttle valve, and Figure 5(c) is the circuit diagram for the equivalent electronic logic gate. The shuttle valve may also be referred to as a disjunction valve. The shuttle valve may be considered as a hydraulically controlled valve as the state of the shuttle valve is controlled using a hydraulic fluid. The shuttle valve may also be considered as a hydraulically operated valve as the moveable element (the ball bearing) of the valve is moved by the action of a hydraulic fluid.

In further detail, Figure 5(a) depicts the shuttle valve having a first inlet A (reference 202), a second inlet B (reference 204) and an outlet C (reference 206). The shuttle valve has a moveable valve element, in this embodiment, a ball-bearing is provided in a T-shaped valve chamber and is moveable by hydraulic fluid. The ball bearing floats between the two inlets and is moveable by incoming hydraulic fluid thus allowing pressure to be obtained from different sources.

The first inlet A is configured to receive a first fluid at a first pressure and the second inlet B is configured to receive a second fluid at a second pressure. The moveable valve element is configured to move in the valve chamber in dependence on the first pressure and the second pressure, in particular, on the difference between the first pressure and the second pressure. The shuttle valve may be considered as an example of a differential valve in which the valve outputs a fluid dependent on the values of the first pressure and the second pressure. In particular, in the present embodiment, the first inlet A and the second inlet B are aligned along a common axis and the moveable element is configured to move in the valve chamber along the common axis. The moveable element can be moved between different positions on the common axis. The shuttle valve allows pressure from two different sources to be provided without a risk of back flow from one source or another.

The movement of the moveable valve element along the common axis places the shuttle valve into a first open configuration, a second open configuration and a third open configuration. In the first open configuration, the moveable element is at a first position by inlet A thus blocking fluid flow between inlet A and outlet C such that no fluidic path is provided between inlet A and outlet C. In the first open configuration, the second inlet B is therefore in fluid communication with the outlet C such that a first fluidic path is defined between inlet B and outlet C. Figure 5(a) shows the shuttle valve in the first open configuration. In the second open configuration, the moveable element is at a second position by inlet B thus blocking fluid flow between inlet B and outlet C. In the second open configuration, the first inlet A is in fluid communication with the outlet C. Figure 5(b) shows the shuttle valve in the second open configuration. In the second open configuration, the moveable element, in the second position, blocks fluid flow between inlet B and outlet C such that no fluidic path is provided between the inlet B and inlet C and such that a second fluidic path is defined between inlet A and C.

In the third open configuration, the moveable element is placed in a position between the first inlet A and the second inlet B such that the moveable element does not block fluid flow from first inlet A to outlet C or from second inlet B to outlet C. In the third open configuration, both the first inlet A and the second inlet B are in fluid communication with the outlet C such that both a first and a second fluidic path is defined between the outlet C and the first and second inlets, respectively.

The shuttle valve is an example of a differential valve that operates in accordance with the logical OR operator (the symbol of which is represented in Figure 5(c)) and reproduced in Table 2. Table 2: OR gate logic table

In use, if no fluid is received at either the first or the second inlets (i.e. no fluid pressure or, in some embodiments, if the fluid pressure is below a threshold value), then no fluid is output from the shuttle valve. If a first fluid at a first pressure is received at the first inlet A and no fluid is received at the second inlet B, the first fluid exerts a force on the moveable element to move the moveable element to its second position at inlet B and the shuttle valve is placed in the second open configuration. In this configuration, the first fluid passes from the first inlet A to outlet C via the first fluidic path and a fluid is thus output via outlet C. Likewise, in use, if no fluid is received at the first inlet A, and a second fluid at a second pressure is received at the second inlet B, the shuttle valve is placed in the first open configuration (moveable valve element moved by second fluid to block first inlet A) such that the second fluid passes from the second inlet B to outlet C via the second fluidic path and is output via outlet C.

If both a first fluid at a first pressure is received at the first inlet A and a second fluid at a second pressure is received at the second inlet B then the operation of the shuttle valve is dependent on the pressure difference between the first and second pressures. In particular, if the first and second pressures are substantially equal the shuttle valve is placed in the third configuration (the moveable element at a mid-point between inlet A and inlet B) such that the first fluid flows from inlet A to outlet C via first fluidic path and the second fluid flows from inlet B to outlet C via second fluidic path, such that both the first fluid and the second fluid is output from outlet C. If there is a difference in pressure then only one of the input fluids will be output via outlet C. In either case, a hydraulic fluid is output via outlet C.

In some embodiments, a first hydraulic fluid at a first pressure may be provided as a first input and a second hydraulic fluid at a second pressure may be provided as a second input to the shuttle valve. In practice, these hydraulic fluids do not mix in the shuttle valve to create vastly varying pressures, rather, the higher pressure provide to the shuttle valve will open the valve. The resolved forces determine the output of the valve and the opening pressure must be greater than the opposing pressure.

In the above-described embodiment of the shuttle valve, it is described that the behaviour of the shuttle valve is such that if either of the inputs are non-zero, then an output is produced. It will be understood that, in some embodiments, the shuttle valve may only provide an input if either of the hydraulic inputs are non-zero and above a threshold value. Such a threshold value will be dependent on physical parameters of the shuttle valve. For example, the minimum pressure required to move the shuttle will depend on, for example, the size and/or dimensions of the first inlet and/or the second inlet; the size/dimensions/mass of the moveable element and/or the size/dimensions of the valve chamber.

The arrangement of valves of the hydraulic demultiplexer may also include an inverter valve. Figure 6(a) depicts a circuit symbol for an example of an inverter valve, in this embodiment, a normally open spring return pilot valve. As described in the following, this inverter valve operates in accordance with the NOT logical operator (represented in Figure 6(b)). The inverter valve is a 3/2 valve having 3 valve ports and 2 configurations (open and closed). The inverter valve is configured to be normally open. As explained in further detailed in the following, when a normally open valve is energized, the valve is sealed such that flow is prevented. If the normally open valve is de-energized, flow is restored. For use in the hydraulic demultiplexer, the energization of the valve is provided by a piloted hydraulic source. This is an ideal valve to demonstrate the negation operation (NOT) logical operation. This valve provides a simple implementation of the negation operation. This valve may also be referred to as a negation valve. A normally open valve passes inlet hydraulic fluid flow when unactuated and blocks flow when actuated. The spring return returns the valve to the normal open position. The inverter valve is a pilot operated valve that is controllable, using a pilot pressure, to be in a first, open, configuration or a second, closed configuration.

The valve has a pilot inlet 302, a supply inlet 304, an outlet 306 and a return outlet 308. A supply fluid channel is defined between the supply inlet 304 and the outlet 306. The valve has a spring-biased actuator, the operation of which is dependent on the pressure of the pressure of hydraulic fluid received at the pilot inlet 302. In particular, the spring- biased actuator is in fluid communication with the pilot inlet 302 such that any hydraulic fluid received at the pilot inlet 302 acts on the spring-biased actuator. The spring-biased actuator has a moveable element provided in the supply fluid channel defined between the supply inlet 304 and the outlet 306. The moveable element may also be referred to as a moveable blocking element.

The spring-biased actuator is configured to be actuated by fluid received at the pilot inlet 302 having a pressure above a threshold, such that, when in an actuated state, the moveable blocking element is moved to a blocking position to block fluid flow between in the supply channel between the supply inlet 304 and the outlet 306. The valve is thus moveable between an open and closed configuration. It will be understood that the precise value of the threshold pressure i.e. the pressure required to block fluid flow is dependent on properties of the spring-biased actuator, for example, the stiffness or spring constant of the spring element. The operating pressure of these hydraulic components may be any suitable hydraulic pressure. In the present embodiment, the operating pressure is 5076.32 psi (350 bar). However, this is will be understood as a non-limiting example of a possible pressure.

In an open configuration, the spring-biased actuator is in an unactuated (de-energized) state. In this state, a first fluid path is defined between the supply inlet 304 and the fluid outlet 306 via the supply channel. In a closed configuration, the fluid path between the supply inlet 304 and the fluid outlet 306 is blocked by the moveable blocking element such that the supply inlet 304 is not in fluid communication with the fluid outlet 306. In the closed configuration, the supply inlet 304 is, instead, in fluid communication with the return outlet 308.

In use, in the absence of an input hydraulic fluid at the pilot inlet 302 or if the input hydraulic fluid at the pilot inlet 302 is below the pressure threshold (the force from the input pressure at the pilot inlet 302 is greater than the spring force), the inverter valve is in the open configuration, and the supply hydraulic fluid flows from the supply inlet 304 to the outlet 306 via the first fluid path. When an input hydraulic fluid is provided at the pilot inlet 302 that has a pressure above the pressure threshold (i.e. the force from the input pressure at the pilot inlet 302 is greater than the spring force) the input hydraulic fluid actuates the spring-biased actuator thus switching the valve to the closed configuration in which the moveable blocking element blocks the fluid path between the supply inlet 304 and the outlet 306. In that case, the supply fluid is instead routed to the return outlet 308.

The inverter valve therefore operates in accordance with the logical OR operator, depicted in Table 2:

In Out

Table 2: Logical OR operator

The normally open spring returned pilot valve described with reference to Figure 6 has the ability to control high pressure lines with a low-pressure pilot and therefore can be used in a hydraulic demultiplexer having two pressures in the system, a stepped down lower pressure for the control of hydraulic and high pressure for operating actuators. This may provide additional capability or enhanced safety with pressure lines.

The inverter valve may be considered as a hydraulically controlled valve as the state of the inverter valve is controlled using a hydraulic fluid (received at the pilot inlet). In addition, the inverter valve may also be considered as a hydraulically operated valve as the moveable element (the moveable blocking element) of the valve is moved by the action of a hydraulic fluid (received via the pilot inlet).

Figure 6(a) may be considered as a simplified valve used for the description of the system. It will be understood that, when the pilot is engaged, a return path for the fluid will be provided. For example, there is a way for the pressure to be relived once the pilot is disengaged. In some embodiments, the hydraulic return path is provided by a small pressure relief valve to the return tank internal to the valve.

The differential valve and the invertor valve described with reference to Figures 5 and 6 may be combined to provide a fluidic or hydraulic logic module, in particular, a logical module configured to receive two input fluid and output an output fluidic in accordance with the logical NOR operator. NOR is the negation of the logical OR operator, and the logic table of the NOR operator is provided at Table 3. Figure 7(a) depicts a combination of the differential valve described with reference to Figure 5 and an inverter valve described with reference to Figure 6. Figure 7(b) depicts the electronic symbol for a NOR operator, the logic table of which is represented in Table 3.

B A Output

0 0 1 1 0 0 1 1 0

Table 3: Logic table for NOR operator

As shown in Figure 7(a), the fluidic logical NOR module has a shuttle valve 400, as described with reference to Figure 5 and an inverter valve 401, as described with reference to Figure 6. The NOR module has a first inlet 402, a second inlet 404 and an outlet 408. The fluidic logical NOR block also has a supply inlet 410 and a return outlet 412. The first inlet 402 of the NOR module corresponds to the first inlet A (202) of the differential valve described with reference to Figure 5. Likewise, the second inlet of the NOR module corresponds to the second inlet B (204) of the differential valve.

The outlet of the differential valve 406 (corresponding to outlet C - 206) is coupled (i.e. in fluid communication) with the pilot inlet of the inverter valve (corresponding to the pilot inlet 302 described with reference to Figure 6). The supply inlet 410, return outlet 412 and outlet 408 of the NOR module correspond to the supply inlet 304, return outlet 308, and outlet 306 as described with reference to Figure 6. While Figure 7(a) depicts a hydraulic logical module, it will be understood that the same functionality may be provided using a different arrangement of valves.

Figure 8 depicts schematic diagrams for a further embodiment of a hydraulic demultiplexer. As described with reference to Figures 3 and 4, the demultiplexer has a single input and four outputs.

Figure 8(a) is a schematic diagram of a 1:4 demultiplexer with four outputs and a single input, controlled by two signal lines. Figure 8(b) depicts how a 1:4 demultiplexer may be formed out of three 1:2 demultiplexer units. In particular, a first output from a first demultiplexer is provided to a second demultiplexer and a second output from the first demultiplexer is provided to a third demultiplexer. The first and second demultiplexers are controlled using a first and second select line, respectively.

As described with reference to Figures 3 and 4, a demultiplexer may be formed out of logical modules. These logical modules may be selected from a functionally complete set. Figure 8(c) depicts a 1:4 demultiplexer formed from NAND modules. The NAND operation forms a functionally complete set. To implement a hydraulic demultiplexer using NAND modules a hydraulic valve operating in accordance with a NAND logical operation is used. Figures 8 to 13 depict a hydraulic valve operable in accordance with the NAND logical operation. The valve is a three position, two port, double pilot operated spring return valve. This NAND module provides a building block for a simple embodiment of the hydraulic demultiplexer to be formed.

Figures 9(a) to 9(d) depicts the valve and its operation. The valve has a first pilot inlet 502, a second pilot inlet 504, a first return outlet 506 and a second return outlet 508. The valve also has a supply inlet 510 and an outlet 512. The valve also has a moveable element in the form of a spool 514 attached to a spring element 520. The spool is provided in a valve chamber. The spool 514 is shaped to allow different fluidic paths to be defined between the supply inlet 510 and the outlet 512 depending on the pressure of hydraulic fluid received at the first and second pilot inlets 502, 504.

A bifurcation channel structure places the outlet 512 into fluid communication with the valve chamber via a first branch 522a and a second branch 522b. The first branch 522a provides a first valve chamber inlet from the valve chamber and the second branch 522b provides a second valve chamber inlet from the valve chamber, the first and second branches forming a Y-shaped junction and being coupled to the outlet 512. In this embodiment, the bifurcation channel structure comprises channels through the housing of the valve, however, it will be understood that the bifurcation channel structure may be provided either as part of the valve and/or may be provided externally of the valve, for example, as external hydraulic fluidic channels.

The first inlet 502 and first return outlet 506 are provided at a first end of the valve chamber and the second inlet 504 and second return outlet 508 are provided at an opposing, second end of the valve chamber. The supply inlet 510 and the outlet 512 are provided centrally. The chamber may be considered to be aligned along a longitudinal chamber axis and the first, second inlets and first and second outlets are aligned parallel to the chamber axis. The spool 514 is moveable along this chamber axis, by sliding. The supply input 510 and outlet 512 can be considered as lying on a supply axis that is substantially perpendicular to the chamber axis. Thus, in use, hydraulic fluid provided to the first and second pilot inlets 502, 504 move the moveable element along the chamber axis.

The moveable member, in this embodiment, the spool 514, when provided in the valve chamber can be considered as defining three smaller cavities, or sub-chambers, in the valve chamber: a first cavity at a first end of the valve chamber, a second cavity at a second end of the valve chamber and a further cavity in mid-region of the valve chamber. The first pilot inlet 502 and first return outlet 506 are in fluid communication only with the first cavity. The second pilot inlet 502 and second return outlet 508 are in fluid communication only with the second cavity. The supply inlet 510 and outlet 512 are in fluid communication only with the further cavity in the mid-region. The spool 514 is shaped, such that, when in the valve chamber, the spool 514 provides a seal between the three cavities such that no fluid is permitted to flow between the three cavities.

The spool 514 is attached to one end of the valve chamber (in this embodiment, to a second end of the chamber by the second pilot inlet 504). The moveable element is moveable between three positions in the valve chamber: a first position, depicted in Figures 9(a) and 9(b), a second positon depicted in Figure 9(c) and a third position depicted in Figure 9(d).

In the present embodiment, the spool 514 has a first groove 516 and a second groove 518. The first groove 516 and the second groove 518 define three blocking portions of the spool: two blocking portions at either end of the spool 514 and a centrally positioned blocking portion. The blocking portions are sized to correspond to the valve chamber such that fluid is prevented from passing each blocking portion when in the valve chamber. The spool 514 and valve chamber interact such that that, when the spool 514 is in the first position (Figure 9(a) and Figure 9(b)) the valve is provided in a first open configuration. In particular, in the first open configuration, a fluidic path is provided between the supply inlet 510 and the outlet 512 via the second groove 518 and the second valve chamber inlet 522b. The second branch of the bifurcation channel structure forms part of the fluidic path.

When the spool 514 is in the second position (Figure 9(c)) the valve is provided in a closed configuration. In particular, in the closed configuration, no fluidic path is provided between the supply inlet 510 and the outlet 512. The central blocking portion of the spool blocks the fluidic path between the supply inlet 510 and the outlet 514 by acting as a seal in the valve chamber.

When the spool 516 is in the third position (Figure 9(d)) the valve is provided in a second open configuration. In the second open configuration, a fluidic path is provided between the supply inlet 510 and the outlet 512 via the first groove 516 and the first valve chamber inlet 522a. The first branch of the bifurcation channel structure forms part of the fluidic path.

As described above, the spool 514 is attached to a spring element. The spool 514 is biased such that in the absence of any forces on the spool (e.g. as in Figure 9(a)) the spool 514 is in the first position and therefore the valve is in the first open configuration. In the natural position (i.e. the first position) the first end of the spool 514 contacts the first end of the chamber. Therefore, any further force on the spool 514 from the opposing end (i.e. due to a fluid received at the second pilot inlet 504) does not move the spool 514. The valve is therefore biased towards the first open configuration. Therefore, the valve remains in the first open configuration in response to receiving a hydraulic fluid at the first inlet 504. The spring 520 and spool 514 are configured such that when the forces on either side of the moveable element have a substantially equal value the spool 514 is placed in the second position corresponding to the closed configuration (as in Figure 9(c)). Figure 9(d) depicts the response of the valve to a force from the first end of the chamber (from first inlet 502) on the corresponding side of the spool 514. The force is sufficient to overcome the spring restoring force and thus the spool 514 is moved to the second end of the chamber placing the moveable element in the third position.

In use, by providing hydraulic control signals in the form of hydraulic fluid to the first and second pilot inlets 502, 504 the configuration of the valve can be controlled therefore switching between permitting and preventing flow between the supply inlet 518 and the outlet 512. The valve therefore operates in accordance with a NAND logic gate, represented in Table 4. If no hydraulic fluid is received at either the first or second pilot inlets 502, 504 or no hydraulic fluid is received at both of the first and second pilot inlets 502, 504, the valve permits flow from the supply inlet 510 to the outlet 512. If a hydraulic fluid is provided at both the first and second pilot inlets 510, 512 then the valve prevents flow between the supply inlet 510 and the outlet 512.

B A Output o o i

0 1 1

1 o 1

1 1 0

Table 4: Logic table for NAND operator

The spool valve described above may be considered as a hydraulically controlled valve as the state of the spool valve is controlled using hydraulic fluid (received at the pilot inlets). In addition, the spool valve may also be considered as a hydraulically operated valve as the moveable element (the spool) of the valve is moved by the action of hydraulic fluid (received via the pilot inlets).

In the embodiment described with reference to Figure 9, a supply hydraulic fluid was controlled using a lower pressure control hydraulic fluid. However, it will be understood that other arrangements of valves can be used, for example, the flow of a lower pressure control fluid may also be controlled using this valve. Figure 10 depicts how two NAND- type valves can be coupled. In Figure 10, a control (lower pressure) hydraulic fluid is provided to the supply inlet of the first valve to be controlled by a second hydraulic fluid provided to the pilot inlet of the first valve. The outlet of the first valve is coupled to the first pilot inlet of the second valve to control a higher pressure hydraulic fluid that is provided to the supply inlet of the second valve. It will be understood that using such principles allows NAND gates to be cascaded to build up a demultiplexer architecture (for example, the architecture shown in Figure 8).

The NAND valve will work with different input pressures. This may be advantageous as there would be less reliance on the bias of the spring. However, it will be understood that this would be specific to the application. Figure 11 depicts a three-dimensional graphical representation of a hydraulic spool valve in accordance with a first embodiment. The hydraulic spool valve operates as described with reference to Figures 9 and 10. Figure 11(a) shows a view of the hydraulic spool valve from a first end. Figure 11(b) shows a side view of the hydraulic spool valve and Figure 11(c) shows a top-down view of the hydraulic spool valve. Figure 11(d) shows a perspective view of the hydraulic spool valve. The spool valve is double pilot operated with a spring return to bias the position in which no pilot signal is provided (i.e. a=0 and b=0). This configuration could be manufactured using a CNC lathe and a CNC mill. In this embodiment, the bifurcation channel structure is provided externally from the valve.

Figure 12 depicts an alternative design of the spool valve, which uses only 2D, or 2.5D manufacturing techniques with stacking and lamination of the spool and valve body. Figure 12(a) shows a view of the hydraulic spool valve from a first end. Figure 12(b) shows a side view of the hydraulic spool valve and Figure 12(c) shows a top-down view of the hydraulic spool valve. Figure 12(d) shows a perspective view of the hydraulic spool valve.

Figure 13 depicts a manufactured prototype of the hydraulic spool valve in accordance with a further embodiment. The prototype has been manufactured using acrylic using a laser cutter. Figure 13(a) is a top-view of the hydraulic spool valve; Figure 13(b) is a side view of the hydraulic spool valve and Figure 13(c) is a perspective view of the hydraulic spool valve. It will be understood that the valve may be manufactured out of different materials. As a non-limiting example, aluminium, 316 stainless steel may be glued together to form a suitable valve.

Certain embodiments of the above-described hydraulic system are configured to be operable at typical hydraulic charge pressures, for example, in the range 500 to 10,000 psi. Typical hydraulic charge pressures in a hydraulic system are in the region 600 to 800 psi. Certain components in a hydraulic system may have applied pressures of 4000- 9000 psi dependent on the system, and a typical maximum working pressure in hydraulic systems is 10,000 psi.

In the above-described embodiments, hydraulic demultiplexers are described. It will be understood that the same principles described herein may be used to build a hydraulic multiplexer. In particular, a hydraulic multiplexer may be provided that comprises an arrangement of hydraulically-controlled and hydraulically-operated valves, similar to the hydraulic demultiplexer. For a hydraulic multiplexer, it will be understood that the common fluidic input of the demultiplexer may be referred to as a common fluidic output of the multiplexer. Likewise, the one or more fluidic outputs of the demultiplexer may be referred to as one or more fluidic inputs of the multiplexer. The hydraulic demultiplexers described above may be inverted and operated as hydraulic multiplexers.

The above-described hydraulic demultiplexers and multiplexers may be used for a number of different applications, and the application of the hydraulic demultiplexers and multiplexers will determine one or more design parameters of the system. For example, in general, applications in a medical environment will use a lower operating pressure than an application in a subsea or subterranean environment. The above description of specific embodiments is made by way of example only and not for the purposes of limitation. It will be clear to the skilled person that modifications of detail may be made within the scope of the invention.