FIELD OF THE INVENTION

The present invention concerns a method and an apparatus to control the vibrations of an articulated arm.

More in particular, the present invention is applied to reduce the vibrations to which the various segments of articulated arms are subjected, used, for example, for pumping concrete in operating machines, such as for example pumps transported on trucks or concrete mixers or similar, whether or not they are mounted on wagons or trucks.

BACKGROUND OF THE INVENTION

Heavy work vehicles are known, used in the building sector, normally consisting of a truck on which an extendable and/or telescopically extractable arm is mounted, articulated for the distribution and the casting of concrete.

The extendable arms of the known type consist of a plurality of segments pivoted with respect to each other and foldable one over the other, so as to be able to assume a folded configuration close up to the truck for transport purposes, and work configurations which allow them to reach areas very distant from the truck.

One of the most important characteristics of these extendable arms is that they are able to reach the greatest heights and/or lengths possible, in order to guarantee maximum flexibility and versatility in use with the same truck.

The increase in the number of articulated segments, or the lengthening of the measurement of each one of them, on the one hand entails the possibility of obtaining greater overall lengths in the maximum extension, but on the other hand entails an increase in weights and bulk that negatively affect the practicality and functionality of the vehicle.

It is also known that a very serious disadvantage in the correct functioning of such arms, which becomes even more serious as the overall length of the arm and the number of segments thereof increases, is the phenomenon of vibrations to which the arm is subjected when it is moved and the concrete is delivered. These vibrations entail considerable operating difficulties both for the operator responsible for manually positioning and directing the pipe through which the concrete exits, and also for the operator who moves the arm by remote control.

The type of these machines and the corresponding characteristics of thinness, inertia and elasticity, have a decisive influence on the entity of the vibrations, since the modes of vibration of the machine itself depend upon them.

In use, the machine works by moving from one configuration of the arm to another. Furthermore, the forced impulsive functioning associated with the piston pump used for pumping the concrete often occurs at frequencies near to those of the machine itself. These effects imply that the vibration modes of the machine, although at different intensities, are continuously excited, generating dynamic variations on the state of stress of the joints and in the material which limit the working life of the machine and reduce safety for the operators.

Document US-A1-2004/0076502 (US'502) describes an articulated arm for pumps transported on trucks, in which a control system is installed for damping vibrations. The control system described therein provides to monitor a parameter that describes the disturbances that lead to a deviation of the position of the arm with respect to a predefined position, for example the determination of the fluctuation in the pressure of the concrete in the distribution pipe, and the load supported by at least one of the units that move the segments of arm.

The control system described in US'502 comprises means to minimize the vibrations that use the load sustained by one of the units as entrance data and emit as exit data a control parameter for the unit that moves the arms.

The control logic described in US'502 uses a so-called target value that defines the desired position of the hydraulic cylinder and hence also the desired position of the segment of arm that is made to oscillate by the respective hydraulic cylinder. Furthermore, a load condition expected on the cylinder is predicted, that is, it is predicted whether the cylinder will be subjected to a bigger or smaller load, and based on this the target value to which the position of the segment must be taken, by means of an overlap device of a variable disturbance, is modified and corrected. Then, on this corrected value, the action of the means to minimize the vibrations is applied and combined, based on the comparison between an estimated load and an actual load detected by pressure detection means associated with the chambers of the actuator cylinders. This solution, using both an estimation of values and also external reference target values to be attained, requires a complex and sophisticated control logic, in which the target value to be reached is followed by a delay ring, taking into account a difference between the value estimated predictively and the actual value found by means of the detections of the sensors.

This solution, as well as weighing down the control circuit due to the calculation complexities, also determines a delay line that makes the system for damping the vibrations rather slow in reacting to situations that vary greatly over time.

One purpose of the present invention is to perfect a method to control vibrations that allows to correct and compensate, substantially in real time, the vibrations of the articulated arm during its movements for the correct positioning of the articulated arm and during the operations to pump the concrete.

Another purpose of the present invention is to obtain an apparatus to control the vibrations of an articulated arm that is simple, economical, extremely rapid in reacting to situations that vary greatly over time, and suitable to work in onerous functioning conditions that occur during the pumping of the concrete.

Another purpose is to obtain a control method and apparatus that does not use predictive techniques or external references to be attained, but obtains the control directly, by recognizing and then canceling the disturbance component in the movement of the arm due to vibrations.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purposes, a method to control vibrations according to the present invention, is applied to an articulated arm comprising a plurality of articulated segments, each associated to a corresponding actuator. The actuators, in their turn, are drivable, on the command of an operator, by means of a hydraulic drive circuit, to make the articulated arm assume a desired configuration such as to allow it to reach a working seating, for example for casting the concrete.

According to one feature of the present invention, during and after the normal movement of the articulated arm, or at least some of its segments, and/or during the pumping step of the concrete determined by the operator, at least a first step is provided to detect the development and entity of the force acting on at least one of the actuators because of the vibrations, and a second step, carried out substantially in real time, during which a processing and command device, as a function of the value of said force detected, commands the drive of a hydraulic control circuit, which is connected fluidically at least to the actuator considered in order to determine the damping of said force due to vibrations.

Detection means are associated to the actuator considered, in order to detect, directly or indirectly, the forces acting on it, and which are caused by the vibratory phenomenon triggered by the movements of the articulated arm, by the inertia in play and possibly, in the case of pumps transported on trucks, also by the vibrations induced because of the pumping of the concrete.

An important characteristic of the control logic according to the present invention is that, so that the control system intervenes, the forces detected in the actuator and due to the vibrations must be different from zero; in other words, the control logic according to the present invention is not based on predictive techniques, nor on external references to be attained, but verifies in real time the existence of pressure forces which determine a differential force in the chambers of the actuator and creates a control action which tends to cancel said differential force.

As a function of the entity and development of the force detected by the detection devices, the processing and control device provides to suitably drive the hydraulic control circuit, in order to feed/discharge work fluid alternately from the actuator so as to dampen the vibrations triggered.

It is advantageous to provide that the method according to the present invention is applied to all the actuators of the articulated arm so as to reduce the damping times of the vibrations and increase the control efficiency.

Moreover, the resultant apparatus to control the vibrations can easily be integrated on board both new and existing machines, and also allows to adapt the apparatus to the particular needs which arise on each occasion.

In accordance with another feature of the invention, during the first detection step the development and entity of a first pressure and a second pressure acting respectively in a first chamber and a second chamber of the actuator considered is detected.

Pressure detectors are associated to each actuator to detect the development and entity of the pressures acting in each of the chambers of the actuator. During the movement of the articulated arm determined by the operator, and during the pumping of the concrete, the work fluid present in the chambers of the actuator is subjected to a determinate pressure due to the weight of the articulated arm, the possible masses in movement and the vibratory phenomenon. The oscillations of the pressure which are detected in the chambers of the actuator are ascribable to the vibrations to which the articulated arm is subjected. The processing and control device is suitable in its turn, substantially in real time, to filter only the component due to the vibrations to determine the actions which must be carried out on the hydraulic control circuit.

According to another feature of the invention, the method provides that, as a function of the geometric properties of the actuator considered, a first force and a second force acting respectively in the first and in the second chamber are determined, and the processing and control device, processing the development and entity of the first force and of the second force, determines the component of said force due only to the vibrations acting on the actuator.

In accordance with a variant embodiment, the detection devices, comprise load cells or extensometers which are associated, for example, to the ends of the actuator to carry out a direct detection of the temporal development and entity of the forces due to the vibrations acting on the actuator.

According to one form of embodiment of the present invention, an electro- valve is associated to the actuator, fluidically connected with the control circuit, and possibly also cooperating with the main feed circuit provided for the normal movement of the articulated arm. Moreover, the method provides that in said second step, the processing and control device sends electric signals depending on the temporal development of the force determined and due to the vibrations, for switching said electro-valve, in order to allow the intervention of the control circuit on the actuator and obtain the damping of the vibrations.

In accordance with another feature of the invention, following the normal movement of the articulated arm, and during the first and second step, a step is provided to control the position and configuration assumed by the articulated arm determined by the operator. It is therefore possible, following the damping interventions of the vibrations due to the hydraulic control circuit, to prevent the articulated arm from assuming a configuration unwanted by the operator. In particular, this control of the position and configuration of the arm uses information relating to the angles formed between the segments of the arm in order to intervene if the control system of the vibrations determines a reciprocal position of the segments which is not correct on the basis of the drive actions imparted by the operator.

In accordance with one form of embodiment, sensors, for example inclinometers, are associated with at least some of the segments of the articulated arm, suitable to detect their position and transmit it to the processing and command device in order to determine the configuration assumed by the articulated arm. Indeed, the method provides that during the control step, the processing and control device detects the signals coming from the sensors.

In accordance with another form of embodiment, in the control step the deviation is determined between the position of the articulated arm or at least part of its segments, determined by the operator, and the instantaneous position of the articulated arm or of the segments, and, if a deviation is determined, the processing and control device determines an action on the hydraulic control circuit in order to keep the articulated arm in the position determined by the operator. It is advantageous to provide ranges of tolerance in the movement, inside which the configuration of the articulated arm can vary without needing to activate the step of controlling the position and configuration assumed by the articulated arm.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is a partial and schematic representation of an apparatus to control vibrations applied to an articulated arm;

- fig. 2 is a schematic representation of an apparatus to control vibrations according to the present invention.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings.

DESCRIPTION OF ONE FORM OF EMBODIMENT

With reference to fig. 1, an apparatus to control vibrations according to the present invention is indicated in its entirety by the reference number 10 and is applied to an articulated arm 1 1 provided with a plurality of segments 12, in this case five segments articulated with respect to each other by respective actuators 13 of the double effect type.

The articulated arm 11, by way of example an arm for distributing concrete, can be installed on a motor vehicle, not shown in the drawings, which allows it to be transported on roads.

The articulated arm 11 is suitable to assume at least a first closed operating condition, in which the individual segments 12 are folded one over the other in a configuration of minimum bulk for transport on roads, and a second extended operating condition, in which the segments 12 assume a configuration desired by the operator in order to reach, for example, a site where the concrete is cast.

The actuators 13 (fig. 2) are driven, in the known way, by a feed circuit 14 of the hydraulic type which comprises an oil-dynamic pump 15, a tank 16 and a control unit 17 commanded by an operator using command means, in this case represented by a joystick 18. The control unit 17 is suitable to feed each of the actuators 13 by means of respective distributor valves 19, each of which is fluidically connected to the individual actuator 13.

Each of the actuators 13 comprises a first chamber 21 and a second chamber 22, separated from each other by the head of a plunger, and each provided with first ports 23 and second ports 24 to feed/discharge the work fluid.

First pressure sensors 25 and second pressure sensors 26 are associated respectively to the first 23 and the second ports 24, and are suitable to detect the pressure inside each of the first 21 and respectively second chambers 22 of the actuators 13.

In the case shown in figs. 1 and 2, the first 25 and the second pressure sensors 26 are installed externally with respect to the first 21 and the second chamber 22, or on the connection pipe between the actuators 13 and the distributor valves 19.

In other forms of embodiment, it may be provided that the first 25 and the second pressure sensors 26 are installed internally to the first 21 and respectively second chamber 22, in order to directly detect the pressures acting therein.

The pressure sensors 25 and 26 can be, merely as an example, piezoelectric transducers.

The apparatus 10 according to the present invention also comprises a hydraulic control circuit 30, which is associated to the hydraulic command circuit 14 and is suitably commanded by a processing and control device 31 to provide the damping of the vibrations to which the articulated arm 11 is subjected during its functioning.

With reference to fig. 2, this shows the control circuit 30 applied only to two of the actuators 13, even if it is obvious that a similar application can be provided for the other actuators 13 as well.

Moreover, dotted lines show the flows of the electric signals processed and detected by the processing and control device 31, while continuous lines show the fluid-dynamic connections.

The control circuit 30 comprises an oil-dynamic pump 34, electro- valves 35 commanded by the processing and control device 31 and each cooperating with the distributor valves 19 and an accumulation tank 36 of operating fluid.

In some forms of embodiment, it is advantageous to provide that the tank 16 of the feed circuit 14 is common to the control circuit 30 too.

A hydraulic accumulator, not shown in the drawings, can also be associated with the control circuit 30 in the known way, and is suitable to keep the fluid under pressure in the control circuit 30 in order to reduce the response times in the control steps.

The oil-dynamic pump 34, in this case, is the axial type with a variable cubic capacity; this allows to control and maintain the working pressure in the delivery pipes always at a more or less constant value, reducing the power dissipated to a minimum value. The cubic capacity of the pump 34 is suitably adjusted by the processing and control device 31 depending on the functioning conditions imposed on the control circuit 30. The electro-valves 35 are provided with a command portion 37 comprising, for example, proportional solenoids which are excited by electric signals, preferably current, sent by the processing and control device 31 in relation to the control activity which must be carried out.

The electro- valve 35, in this case, is the proportional four- way type and when switched allows the oil to pass in the distributor valve 19.

The distributor valve 19 therefore adjusts the passage of work fluid coming from the hydraulic feed circuit 14 during normal movement, and regulates the work fluid coming from the control circuit 30 for damping the vibrations.

Sensors are provided to determine the position assumed by the segments 12.

In this case, the sensors comprise inclinometers 40, solidly attached to the segments 12, even if in other forms of embodiment sensors may be provided to detect the reciprocal angle assumed by each segment 12 with respect to the preceding or following segment, or linear position sensors able to determine the instantaneous length of each actuator.

The signals detected by each of the inclinometers 40 are sent to the processing and control device 31 to determine the overall configuration of the articulated arm 10.

The method to control the vibrations of an articulated arm is now described. The articulated arm 1 1 is moved, by means of the feed circuit 14, as a function of the signals coming from the joystick 18 and imparted by the operator to assume a desired configuration such as to allow the arm 11 to reach for example a seating where the concrete is cast.

The processing and control device 31 is able to detect the movement condition associated to the operator's command and the pumping condition and, if one of these conditions occurs, starts the method to control and damp the vibrations of the articulated arm 11. In non- working conditions, which do not cause vibration effects, and identifiable by the fact that the operator does not send movement or pumping commands for a pre-established time, it is useful that the control device, even if continuing to monitor the condition of the articulated arm 11, does not send signals to the electro-valves and sends the cubic capacity of the pump to the minimum value, in order to save fuel and wear on the components.

During the movement of the articulated arm 11, the latter, because of the effects of pitching, because of effects due to the pumping of concrete through the piping, and/or because of inertial effects of movement of the masses, is subjected to even very strong vibrations.

A step is therefore also provided, by the first 25 and second pressure sensors 26, to detect over time the pressures acting in the first chamber 21 and in the second chamber 22 of each of the actuators 13.

The signals detected substantially continuously, that is, at very small intervals of time, by the pressure sensors 25, 26 are sent to the processing and control device 31.

A step thus follows of processing the signals sent by each of the first 25 and second pressure sensors 26 during which the action is determined which must be performed on the control circuit 30 for damping the vibrations.

In particular, as a function of the pressure signals detected by the sensors 25, 26, the development and entity of the actual force acting in each chamber 21, 22 of each actuator 13 is determined. It is obvious for the person of skill that this actual force is also determined as a function of the geometric properties of each actuator 13, that is, as a function of the useful section of the head or bottom of the actuator 13.

During this processing step, it is also provided to determine the differential force, calculated as the difference between the force acting in the first chamber 21 and the force acting in the second chamber 22. This differential force, suitably processed by the processing and control device 31, supplies an indication of the entity and development of the vibrations to which the articulated arm 1 1 is subjected.

More specifically, the differential force is filtered of its component of average value so as to obtain only the component of force acting on the actuator 13 due to the vibrations which arise. In particular, the filtering of the average value of the differential force between the forces acting in the two chambers 21, 22 allows to obtain only the dynamic component associated to an oscillation of the segment of the arm: this component is equal to zero when the segment is not moving, even if the absolute force inside the chambers of the cylinder can be different from zero.

Starting from this information, the processing and control device 31 determines an action step on the control circuit 30. In particular, since the temporal development and entity of the force acting on each actuator 13 and due to the vibrations are known, the control circuit 30 is commanded to apply on the actuator 13 an input of work fluid, for example oil, into the two chambers 21, 22 such as to generate a force which opposes the force associated to the vibrations.

More specifically, the processing and control device 31 generates electric signals to be sent to the command portion 37 of the electro-valve 35 associated with the actuator 13 considered, the entity of which depends on the temporal development of the force associated to the vibration.

It is advantageous to provide that the electric signals are current signals which act by induction on the proportional solenoids of the command portion 37.

The electro-valve 35 is therefore suitably switched to send the work fluid alternately in one chamber 21 or the other 22 of the actuator 13, so as to determine the damping action.

During this action step, the processing and control device 31 also provides to regulate the functioning of the pump 34 of the control circuit 30, for example modifying its cubic capacity, in order to keep it at a constant pressure.

During this action step on the control circuit 30, the geometric configuration assumed by the segments of articulated arm 1 1 can be modified, even if only by a little.

The method can also comprise a step of controlling the position and configuration assumed by the articulated arm 1 1 during the action of damping the vibrations. This step allows to maintain the positioning of the articulated arm 1 1 in the position determined by the operator for the execution of the desired operations.

The step of controlling the position and configuration of the articulated arm 1 1 is activated after the commands set by the operator, and also as a function of the actions of damping the vibrations of the articulated arm 1 1.

It is advantageous to provide that the step of controlling the position and configuration is actuated after a determinate interval of time has passed, for example some seconds, since the last movement of the articulated arm 1 1 determined by the operator.

After this interval of time has passed, and if no further movement commands arrive from the operator, the processing and control device 31 determines the configuration assumed by the segments 12 of the articulated arm 11 on the basis of signals read by the inclinometers 40.

At the same time as this step, the actions for damping the vibrations are activated, as described above, during which there may be variations in the inclination of the individual segments 12.

More specifically, at regular intervals of time, the deviation between the position assumed initially by the articulated arm and the instantaneous position thereof is determined, which is varied due to the variations in position to which the articulated arm is subjected during the action step on the control circuit 30 for damping the vibrations.

As a function of this deviation, the processing and control device 31 provides to determine the actions which must be applied to the control circuit 30 in order to reposition and/or maintain the position of the articulated arm 1 1 in the configuration desired and determined by the operator.

The actions of repositioning the articulated arm 1 1 occur by sending signals to the electro-valves 35 of each, or at least some, of the actuators 13, which in their turn determine the passage of work fluid into one or other chamber of the actuator 13.

It is clear that modifications and/or additions of parts may be made to the method to control the vibrations of an articulated arm and the corresponding apparatus to control the vibrations as described heretofore, without departing from the field and scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of method to control the vibrations of an articulated arm and the corresponding apparatus to control the vibrations, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.