Field of the invention

The present invention relates to machine elements integrated with sensors.

Background of the invention

Many interactive devices use both machine elements and sensors, simultaneously but redundantly enabling and measuring the same physical function.

Sensors and machine elements are key components in the construction of many interactive devices. Machine elements determine the potential of a device's physical freedom, while sensors measure the actual use of this potential.

In many designs these two families of elements are used together, but the integration between them has not been explored, as designers still rely on traditional separation between machine elements and sensors.

For combining sensors with machine elements, presently known solutions offer approaches described, for example, in [7,18].

Like sensors, machine elements come in a variety of types and meet a wide range of needs, satisfying structural requirements, and controlling motion and/or user mechanical input [21]. Bearings, axles, seals, gears, screws and other elements are produced in mass quantities, reducing their cost to bare minimum. While offering an extensive portfolio of designs, the industrial standards that dictate the forms and dimensions of such elements limit design freedom, introducing rigid constraints on the making process.

Additive Manufacturing (AM) calls for a revision of traditional disciplinary boundaries [3], enabling designers to produce specific solutions for specific needs. AM of metal parts makes conductive objects that can be used to 3D print sensors, and complicated 3D structures that can be used to 3D print machine elements [15].

Several recent 3D printing projects have demonstrated designs with a high degree of mechanical freedom [28,29]. Along the same lines, Schmitt offers a parametric design procedure to customize 3D-printed machine parts, taking into consideration the specifications (tolerance, resolution) of a given 3D printing technology [10]. Yet in many cases, designers and engineers are bound to traditional design paradigms, paralleling mechanical and sensorial systems.

For example, in [12] the researchers 3D printed two parallel gear systems. One converted a servomotor's rotary motion to linear motion, while a second measured movement on the same axis.

In Human Computer Interface (HCI) projects, researchers have already started to explore the intersection of 3D printing and interactive components, as in the 3D- printed optics by Willis et al. [27]. In the last several years a vast body of work has been published on 2D-printed (customizable) electronics and sensors [4,7,9,14], and we can expect the development of fully functional 3D-printed electronics, likely beginning with conductive traces layered on a 3D model, etc., as suggested by Voxel8 [16].

Nevertheless, today the principle of combining the machine elements and the sensors still remains conventional both in design and in practice: structure and functions of the machine element block are traditionally separate from structure and functions of the sensing block.

Object and Summary of the invention

It is an object and a concept of the invention to merge the above-discussed two families of components, seeking to form a new family of design primitives being both efficient (saving space and material), and interactive hybrid elements, each constituting a machine component and a sensor simultaneously.

According to a first aspect of the invention, there is provided a hybrid element being simultaneously both a machine component and a sensor integrated so that

parts of the hybrid element, performing mechanic functions and sensing functions of said element, are the same. Owing to such an arrangement, in operation, signals of the sensor are echoing (responding to) the mechanical functions of the machine component.

The machine component of the hybrid element may be designed based on a standard design thereof.

Alternatively or in addition, the machine component may be designed so as to ensure its functioning also as a sensor.

Further, the Inventors propose that the hybrid element's design is 3D printable.

The machine component of the proposed hybrid element may be selected from a non- exhaustive list comprising: a ball bearing, a gear, a hinge, a screw.

The sensor may be selected from a non-exhaustive list comprising: a rotatable motion sensor, a linear motion sensor, an angle sensor, a force/pressure sensor.

In other words, the hybrid element is interactive in the sense that it is designed to report by its integrated sensor about the hybrid element's condition (for example, motion or static position, type of motion, displacement or distance, angle/angular position, angular speed, exposure to force or pressure).

The hybrid element may be covered by an insulating layer so as to prevent instable work of the hybrid element caused by capacitance of the surrounding, for example of human skin.

The hybrid element (actually, its sensor) may be connectable to at least one of the following: a communication means (interface), a processing unit, a displaying unit. For example, such an interface may require physical contact with the element or may be contactless/wireless, such a processing unit may be a microprocessor or any computer. Depending on implementation, the interface, the processing and/or the displaying unit may be embedded (integrally incorporated) in the hybrid element, but may be external. The hybrid element may thus represent an intelligent construction element adapted to supply real-time instructions and/or alarms in potentially dangerous situations. For example, such intelligent construction elements can virtually mirror the building process or condition of the building and thus supply comprehensive real-time instructions and alarms.

Therefore, and according to a further aspect of the invention, the Inventors propose an analog/digital system, mirroring one or more said hybrid elements (i.e. the physical elements) and their performance. It may be implemented in a real environment and/or in a virtual environment (for example, a PC environment).

The system may be designed for collecting, processing and displaying measurements of said hybrid elements' sensors.

For implementations of the proposed hybrid elements which will be listed below: the hybrid screw may initiate alarms on dynamic or static overpressure in various constructions. The hybrid hinge, bearing, gear - when used in a door/window/shutter/gate/etc. mechanism may initiate "open-closed" indications and intrusion alarms in real time. The hybrid bearing may supply real time data and alarms on angular speed.

Such and other hybrid elements may form part (e.g., form a new interactive space) of a virtual environment, for example a Human Computer Interface (HCI).

In other words, the Inventors also propose using the hybrid elements in various interactive systems, as they offer a new interactive capability of performing while measuring (and measuring while performing) in a single unit. The Inventors have leveraged recent developments in 3D printing to embed sensing in metal structures that are otherwise difficult to equip with sensors.

In other words, the Inventors also propose designing the hybrid elements to be 3D printable ( as mentioned above), and then using Additive Manufacturing (AM) i.e., 3D printing of metal and other structures to hybridize the proposed systems, thus developing specific solutions of the hybrid elements while reducing cost and space. More specifically, the Inventors present at least the following four implementations of the concept, respectively comprising:

(1) a force/pressure sensor within a screw, being a hybrid screw capable of detecting force/pressure applied to the screw, for example a critical/threshold value thereof. The hybrid screw can be fulfilled with a suitable screw-driver, for example comprising the processing/displaying unit of the hybrid screw, thereby forming a hybrid system with the hybrid screw. The sensor may comprise a pressure-sensitive conductive layer.

(2) a rotary motion sensor (for example, an electronic switch) integrated within a ball bearing, being a hybrid ball bearing capable of sensing rotation motion/ rotation speed;

(3) a linear motion sensor (for example, a voltage divider) within a gear such as a worm gear, being a hybrid gear capable of sensing linear motion /distance/position;

(4) an angle sensor variable capacitor embedded in a hinge, being a hybrid hinge capable of detecting angle formed by the hinge;

Each design (hybrid element) demonstrates a different sensing principle, and signals its performance through one or more of the following (1) movement; (2) position; (3) angle (4) or stress.

The Inventors have actually succeeded to free the design of sensor and machine elements from industrial standards, integrating sensors into structures with complex physical constraints using existing AM material and processes.

There is proposed a new family of double agent elements— facilitating mechanical performance while evaluating the same performance .

In the proposed hybrid elements/machine components, mechanical actions (such as angular and linear movement, motion transmitting, and structural alignments) and sensorial (electromagnetic) measurements are executed by the same performing parts of the hybrid element, in contrast with the idea of simply combining sensors with machine elements as current solutions offer [7,18]. Additive manufacturing (AM) -which is also called 3D printing technology - may be used for producing the hybrid elements according to the concept of the invention.

The Inventors 3D printed the following examples of the proposed hybrid elements: (1) a hybrid screw with an embedded sensing mechanism to measure force/pressure applied to a screw, and a suitable screw-driver;

(2) a hybrid ball bearing with an embedded differential rotary motion detector ( in the form of a switch embedded in the ball bearing);

(3) a hybrid linear gear with an embedded differential linear motion detector in the form of a voltage divider embedded in the linear gear;

(4) a hybrid hinge with an angle detector using a variable capacitor in the shape of a hinge axle.

The mentioned hybrid elements: ball bearing, gear, hinge, screw were designed and further manufactured to perform as similarly as possible to traditional machine elements, yet with small structural changes that enable them to function as motion, angle, and pressure sensors , i.e., to produce electronic signals echoing their mechanical performance. Specific embodiments of the proposed hybrid element will be now discussed.

In one specific embodiment, the hybrid element is manufactured as a screw integrally incorporating a screw head, a screw body (stem) and at least one embedded layer of pressure- sensitive conductive material.

For example, said at least one layer may be placed between the screw head and the screw body.

More specifically, the screw may comprise an electrically insulating disc placed so as to position said at least one layer of the pressure-sensitive conductive material between the screw head and the screw body.

Still further, the screw may comprise a pressure disc placed between the insulating disc and the screw body.

The pressure sensitive material may be a SDR (static discharge release) material. For example, the pressure sensitive material may be Velostat™. Velostat is a thin (of about 0.1mm) pressure-sensitive conductive material: squeezing it will reduce the resistance [25].

The hybrid screw element may be 3D printed.

In order to detect change of resistance of said layer of the pressure-sensitive conductive material upon applying pressure to the screw, a screwdriver may be provided for making contact with said hybrid screw and receiving therefrom an electric signal indicative of resistance of the pressure-sensitive conductive layer(s).

More specifically, the screwdriver may form an electric circuit with the hybrid screw when contacting it. The electric signal may be further used to judge about pressure applied to the screw and thus to its pressure -sensitive the conductive layer (s). Actually, the pressure applied to the screw is pressure of reaction, created by the wall into which the screw is being screwed.

For example, the electric circuit may be formed so as to include said layer of pressure- sensitive conductive layer of the hybrid screw. The screwdriver may be in communication with a processing and or a displaying unit for processing the electric signal and/or displaying the pressure being currently applied to the screw relatively to a maximal pressure applicable to said screw.

The screwdriver may incorporate said processing and/or displaying unit.

The processing unit may be a microprocessor/microcontroller, for example an Arduino tool.

In a presently developed implementation, the electrical circuit between the hybrid screw and the screwdriver is closed when the two elements make contact. However, other implementations are possible, for example for wirelessly measuring resistance of the hybrid screw. The screw-driver may be 3D printed as well.

According to a further aspect of the invention, there is also provided a kit comprising the hybrid screw and said screw-driver.

According to still a further aspect of the invention , there is provided a system comprising two or more of the hybrid screws utilized in a structure ( for example, in a building), wherein the pressure sensors of the hybrid screws being in communication with a central processing unit, for estimating current loads in different points of the structure and reliability of the structure.

According to yet another aspect of the invention, there is provided a method of performing measurements of pressure applied to a screw, the method comprises: providing said screw being a hybrid screw integrally incorporating a screw head, a screw body and an embedded layer of pressure- sensitive conductive material ,

measuring electrical resistance of the hybrid screw,

applying pressure to the hybrid screw ( it may be pressure of reaction, when screwing the screw into an object such as a wall),

- judging about value of the applied pressure based on changes in electrical resistance of the hybrid screw upon applying the pressure.

The method may comprise using the described screw-driver for applying pressure to the hybrid screw, obtaining data indicative of electrical resistance of the hybrid screw ( for example, voltage readings from the hybrid screw or from the pressure- sensitive layer) and communicating the obtained data to a processing unit (which may be embedded in the screw driver, or external).

According to still a further aspect of the invention, there is finally provided a computer software product, comprising a computer readable medium in which program instructions are stored, which instructions, when read by a processing unit, cause the processing unit to receive data indicative of electrical resistance of the hybrid screw and execute the above method.

The software product can be implemented, for example, as a firmware serving as said computer readable medium. The firmware may be embedded, for example, on an Arduino microcontroller board.

According to another embodiment of the hybrid element, it is a ball bearing hybrid element comprising a ball bearing integrally incorporating one or more electric or electronic switch switchable by rotary motion of balls in the ball bearing. Such a hybrid element may be called a Switch Ball Bearing or a ball bearing with an embedded rotary motion detector. It may be used for detecting a rotation angle and an angular speed.

It is known that a conventional ball bearing mechanism is usually installed between a fixed axle and a rotating part (or vise versa), so that a fixed part and a rotating part are separated by a ring of small balls that reduce rotational friction and support loads.

Actually, the proposed ball bearing hybrid element integrally incorporates an angular motion detector in the form of one or more said electric or electronic switches, adapted to count angular portions (or arcuate trajectories) passed by balls running in the ball bearing during the rotary motion.

The detector may be called a differential rotary (or angular) motion detector (i.e., detector of rotary speed). Frequency of electric locking of the mentioned switches will be indicative of the radial speed of interest .

The detector may be connectable to a processing/displaying unit, for example a microprocessor . Depending on specific implementation, such a unit may be integrally incorporated in the ball bearing hybrid element, but may be external. The electronic switches may be two-way single pole switches, for example four such switches (Figs. 6c, 6e) counting quarter circles (arcs or angles of 90 degrees rotation movement) in the ball bearing. The hybrid ball bearing element may be 3D printed.

For example, it may be printed from bronze and nylon. For example it may be 10.3 mm wide and have radii of 12, and 17.1 mm for the inner and outer rings of the ball bearing).

The hybrid ball bearing may comprise a conductive outer ring for supporting its inner structure including an inner ring and balls, the conductive outer ring enclosing two conductive side rings isolated from one another and from the outer ring (see Fig. 6a- b), wherein each of the conductive side rings has one or more pins forming said one or more switches (for example, four pins spaced by 90 degrees from each other, see Fig. 6c).

For isolating the conductive outer ring from the conductive side rings, the hybrid ball bearing may comprise an isolating (for example a nylon) case consisting of a number of isolating rings defining

a space between the inner ring and balls, and

- an angular distance between pins protruding towards one another from the respective two conductive side rings and forming contacts of each of said electrical switches.

In operation, the outer ring of the ball bearing may be permanently grounded, both of the side conductive rings may be supplied with voltage (for example, of 5V), and each the side rings may be connected to an analog contact on said microcontroller, for registration of electric locking (switching) when takes place at any of said electronic switches when a ball locks it.

During rotation of the ball bearing, contact with the outer ring may be made by balls with either pin of an electrical switch (or both simultaneously). When the outer ring makes contact, the current flows to ground through a resistor ( Fig. 6c), bringing the analog contact from 5V to ground.

In one specific embodiment, four switches (i.e. four sets of 2 pins) may symmetrically be provided along circumference of the hybrid element and be connected to the inner and the outer rings. Because of the symmetry of the arrangement, electric contact can be made simultaneously at the four switches by 4 respective balls at a time, while all of these close the same electrical circuit. Therefore, frequency of electric locking of that circuit will indicate the radial speed in the ball bearing.

To best evaluate the performance of the hybrid ball bearing, analog data polling can be used to monitor the voltage on the pins. However, digital polling may be used for some practical applications.

In the suitable software or firmware of the processing unit (microprocessor), the angle counter may be set to 0 on a specific ball upon initiation. The firmware may sample the analog pins periodically, and may then detect the contact between the side and the outer ring. The sequence of input samples may then be used to determine the rotation angle and the angular speed.

The proposed hybrid ball bearing can be used, for example, in high-end, professional mountain or road bicycles.

According to yet a further embodiment, the hybrid element may comprise a gear simultaneously constituting a voltage divider adapted to be used as a sensor of linear displacement. Such a hybrid element may be called Voltage Divider Gear.

As known in the art, a gear is often a set of toothed elements, either wheels or linear bars that work together to transfer one type of driving force to another. While the applications for gears are innumerable, here is presented an example of a simple system with a toothed wheel and a toothed linear gear that transfers rotation to linear motion. In one example of implementation, the Inventors have revised a traditional linear gear (also called track, 67 x 8.5 x 11.9 mm) by creating repeating sequences with 4 teeth in each sequence, connected together to a single housing using NyTek™ 1200 CF (nylon 12 with carbon) SLS (wherein SLS is an additive manufacturing technique). Such an implementation allows demonstrating the principle quite easily. Potentially, there can be as many sequences as required for the gear system. The main industrial use of NyTek™ 1200 CF is to improve the thermal performance of nylon 12 as a common SLS material. However, the conductivity of the carbon also makes it a good resistor [1]. It was an idea of the Inventors to implement conductive elements of a traditional linear gear as a voltage divider. For example, the voltage divider may be arranged between the toothed wheel and each one of the four alternating-tooth systems.

In essence, the gear moving on the track, functions as a potentiometer— by changing the resistance of the circuit as it moves on the track, it also changes the voltage on the wheel. For example, the track of such a hybrid element may comprise repeated sequences of resistors connected in series.

Similarly as in other embodiments, the above-mentioned hybrid gear may incorporate there-inside/ be connectable to a processing unit. For example, the processing unit may be implemented as an Arduino board.

As other discussed hybrid elements, the hybrid gear element may be manufactured by 3D printing.

According to yet a further embodiment, the hybrid element may be a hybrid hinge constituting a variable capacitor serving as a sensor of angular displacement of the hinge. The hybrid hinge may be called a Variable Capacitor Hinge.

As standard hinge allows an angle of rotation between two elements, and may comprise a circular bearing mechanism ( a hinge axle) between two joints (for example, the joints may constitute or connect to the axle , terminals such as curved plates, etc.).

The change in capacitance results from the change of coinciding surface areas of the two terminals of the hybrid hinge, as the terminals move.

The Inventors propose one exemplary implementation of a variable capacitor hinge that relies on the device's circular bearing (for example, using 45.6mm from the hinge's total length of 65mm), where one rounded conductive surface (for example, 4.2mm radius) is movable around a second conductive rounded surface (for example, 4.95mm radius), being a first and a second conductive terminals of a capacitor. As these surfaces move, their overlapping areas (the capacitor's terminals) change, thus changing the potential capacitance between them (see Fig. 13). By measuring the device's capacitance, we can determine the angle of the hinge.

The hybrid hinge may comprise a processing and/or a displaying unit capable of measuring the capacitance and determining the angle of the hinge based on the measured capacitance. The unit may be a microprocessor/microcontroller, for example an Arduino tool ( such as "Arduino Uno").

The hybrid hinge may be 3D printed. For example the hybrid hinge may be 3D printed using bronze for printing conductive capacitor's terminals and using nylon and glass for printing insulating portions of the variable capacitor.

The invention will be explained in detail as the description proceeds. Brief description of the drawings

The invention will be further described with the aid of the following non-limiting drawings, in which:

Figs. 1 illustrates four exemplary proposed hybrid elements: hybrid gear, hybrid hinge, hybrid ball bearing and hybrid screw with a screwdriver.

Figs. 2 a, b schematically illustrate the design of the hybrid pressure-sensing screw , its screwdriver and an analog circuit for obtaining information from the embedded pressure sensor.

Fig. 2c is a pictorial illustration of one way to obtain readings from the hybrid screw.

Fig. 3 is a schematic diagram illustrating relative strength of the proposed 3D printed hybrid screw in comparison with a conventional screw.

Fig. 4 shows voltage readings of pressure obtained from the hybrid screw.

Figs. 5 a-e show an exemplary design and one suitable analog circuit of a ball bearing hybrid element .

Figs. 6 a- c illustrate an exemplary data flow from a hybrid ball bearing to its virtual model.

Fig. 7 shows exemplary voltage outputs obtained from the hybrid ball bearing.

Figs. 8a, 8b illustrate simulation results demonstrating strength of the proposed hybrid ball bearing, compared with strength of a standard ball bearing. Figs 9 a-c illustrate a hybrid gear element, its exploded view with three separate teeth systems, and its electric circuit.

Figs. 10 a, b show simulation results illustrating strength of the hybrid gear element in comparison with a standard gear.

Figs. 11 a -c present voltage measurements taken from three different sets of teeth. Figs. 12 a-c show an exemplary design of the hybrid hinge and its electric circuit. Figs. 12 d-f present examples of utilizing the hybrid hinge for measuring angle of the hinge by its embedded capacitor sensor, and for controlling a virtual system based on the measurements.

Figs. 13 a, b show simulation results demonstrating relative strength of the hybrid hinge compared to a standard hinge.

Fig. 14 shows measured capacitance values corresponding to hinge's opening angles.

Detailed description of specific embodiments

The Summary has presented a new approach to augmenting machine elements with sensing capabilities so as to obtain so-called hybrid elements, for example by using AM (3D printing). While machine elements of the hybrid elements act in the physical domain, and their sensors are used to report on the virtual one, the proposed hybrid elements may be used in various interactive systems, where they may communicate with individual or centralized processing and/or displaying units. Further, four exemplary hybrid elements will be described in detail. In addition, simple analog/digital systems, mirroring the physical devices and their performance in the virtual (PC) environment, will be described.

The hybrid elements are interactive units equipped to perform while measuring and vice versa, which can be successfully used in HCI.

The Inventors' evaluations show that while there are a few technical limitations that can be improved, the designs of the proposed hybrid elements are reliable and stable. Currently there are several AM technologies available from online services that enable digital fabrication of metal parts. The high-end process offered by Stratasys provides full sintering of metal powder using Direct Metal Laser

Sintering (DMLS) for stainless steel, titanium, aluminum and other alloys [13]. While this is a costly process (see below), cheaper options are available from Shapeways [11] and i.materialize (being a 3D printing company). A hybrid printing/casting option is offered for metals with lower melting points, such as brass, bronze, silver, and gold. These materials can be easily cast from 3D-printed wax models. An even cheaper hybrid option (with probably the lowest resolution) digitally layers steel powder (60%) and deposits it with melted bronze (40%).

The Inventors evaluated the structural performance of the new hybrid elements with the Finite Element Method (FEM), and also ran electronic performance measurements and analysis (which will be mentioned further on in the Detailed Description). Fig. 1 illustrates four proposed exemplary 3D-printed metal machine elements augmented with sensing abilities, i.e. four exemplary hybrid elements. From left to right: a voltage divider 10 integrated inside a gear 100; a variable capacitor 12 embedded in a hinge 112; an electronic switch 14 within a ball bearing 114; and a pressure sensor 16 within a screw 116 (and its dedicated screwdriver 117).

Figures 2a and 2b illustrate an exemplary design of the 3D-printed Velostat pressure- sensing screw and its screwdriver and a suitable analog circuit.

The design proposed by the Inventors relies on a known sensing material, embedded in the screw. Velostat is a thin (of about 0.1mm) pressure-sensitive conductive material: squeezing it will reduce the resistance [25]. The exemplary proposed 3D- printed screw 116 (shown in Fig. 3b) comprises a special insulating disk/ring 15 isolated from the main body of the screw 116, located between the screwhead 11 and the base surface 13 (the radius of the screwhead being 7.9mm). Three layers of Velostat sheets 18 were placed between this ring 15 and the screwhead 11. When the screw is driven into a surface, it changes its resistance due to pressure applied to the ring 15 . Fig. 3 shows an example where the Velostat element 18 and the ring 15 form part of the screw head 11, being its extension.

A special 3D-printed screwdriver 117 can read this pressure while driving the screw 116 (see also Figs. 2b, 2c).

Fig. 2b illustrates an exemplary principle to measure the pressure applied to the screw 116. Since the screw changes its resistance as pressure is applied, the best way to deduce its resistance at a given time is by using a simple voltage divider circuit. To measure its value, we may connect the screw in series to R ₂ (using the special screwdriver; for example, a 5KOhm resistor) and supply it with an incoming voltage of 5V. For the unknown resistor Ri of the screw, a resistor with a known value 7¾=5K, input voltage Vi _n =5V, and the sampled voltage V _ou t, we can easily find R = ¾( Vi _n /V ₀ ut- l) ^"1 . An additional pulldown resistance R3 for the input pin may be of about lOkOhm.

In a similar vein with the previous components, the firmware samples the Vout every 100ms and averages the result with the adjacent samples, after which it calculates the resistance with the given formula. A simple Grasshopper program may display a visualization of the change in the screw's location, based on the assumption that a rise in pressure indicates change in position. In practice, the proposed sensor may be provided with visualization (display) means incorporated in the screwdriver.

Alternatively, the proposed hybrid screw, when being part of a construction, may communicate signals responsive to pressure currently applied to the screw, towards an external processing and/or display means.

Fig. 2c shows an operation scenario of one embodiment of the hybrid screw 116 (the embodiment called Velostat screw) and the dedicated screwdriver 117 which is designed to read the information from the screw 116 while driving it. The wires and the chips (such as Arduino controller 13) are shown for illustrative purposes. They demonstrate that in the laboratory, the output signals received from the screwdriver when it contacted the screw, were transmitted to a processor and further processed. In practice, a microprocessor like the Arduino controller 13 may be incorporated in the screwdriver. Display means may be built in, or may be external. Communication means may be wireless. The whole control package comprising communication means, display means and the controller, is marked 13.

Fig. 3 presents the Hybrid Screw Performance evaluation. The FEM-simulation of torque was applied to the screw (500KNm), in the direction of the screwing axis, tested on the proposed screw design 116 (left-hand image) and compared to a standard design (right-hand image 9). Darker colors represent risk (danger) to structural integrity. Compared to the traditional screw design, the additional ring or disc 15 with the layer 18 placed underneath the screwhead 11 does not significantly weaken the screw's structure 116. Only when the screwhead is subjected to an extreme (and unrealistic) pressure, some differences in the FEM simulation between the proposed design and a traditional (standard) one can be detected (see Fig. 4). Such differences are not considered a significant concern.

The resulting sensor 16 is very sensitive. A slight change in pressure on the screw is enough to change its resistance in the realm of KOhms. The electrical output may be easily toned down to achieve a workable data set. Fig. 4 shows a graph of the voltage (indicating the screw resistance), obtained for various levels of pressure on the screw, namely voltage values of the screw measured by the Arduino 13 as a function of applied force (measured at 0, 125, 375, 500, 625 & 750 g). The plot is a spline interpolation. The darkest color area M represents the mean with the standard deviation around it, where most of the data was found.

Any change in voltage represents KOhms of change in resistance. As the presently available evaluation reveals, the screw is highly sensitive to a value range of about 125-750g. Further evaluation for higher values may be easily performed.

Figs. 5a-5d illustrate one proposed implementation of the hybrid Ball bearing 114. Fig. 5e is an analog circuit design. It shows an electrical circuit of an angular motion detector/sensor 14 integrated in the hybrid bearing 114; the sensor being a two-way single pole switch which is actuated by a rotating ball 26 and is thus capable of counting quarter circles (90 degrees rotations).

Figs 5a-5d show an exemplary design of the 3D printed switch ball bearing 114 using bronze, nylon, and steel balls.

Any ball bearing mechanism is arranged between a fixed part 22 and a rotating part (axis 25 in Fig. 1, not shown in Figs 5) , separated by a ring 24 of small balls 26 that reduce rotational friction and support loads. Ball bearings come in a diverse range of shapes and sizes, and can be made from a variety of metals, plastics, and even ceramics. Bearings are fundamental in any mechanical design with degrees of freedom, as they allow movement. While we relied on a common ball bearing design, our solution will also fit alternative ball bearings. Our exemplary ball bearing 114 (printed from bronze and nylon 12, 17.1 mm radius, 10.3 mm wide) implements a differential angular motion detector 14 in the form of a two-way single pole switch (Fig. 5e), counting quarter circles (90 degrees rotations). The outer ring 22 supports the whole inner structure, and encloses two isolated side rings 23a, 23b (see Fig. 5 a-b). Each of these side rings has four pins 21a and 21b (90 degree from each other, Fig. 6c) inside, but isolated from, the outer ring 22. A nylon case 27 sets the angle between the inner ring 24 and the balls 26, Rings 29a and 29b are isolating rings.

The outer ring 22 of the ball bearing is grounded at all times. Both side rings 23a, 23b are supplied with a voltage of 5V, and each is connected to an analog pin on a microcontroller (for example Arduino, not shown in this drawing). During the rotation of the ball bearing, contact with the outer ring may be made, through a ball 26, by either pin (or both pins 21a, 21b simultaneously). When the outer ring 22 makes contact, the current flows to ground through a resistor, bringing the analog pin from 5V to ground.

Figs. 6a, 6b 6c illustrate the ball bearing sensor performance. They show a dataflow from the physical machine element, Hybrid ball bearing 114 ( as shown in 6a), to its virtual model ( schematically shown in 6b) using Grasshopper ( schematically shown in 6c), Firefly and Arduino.

To best evaluate the performance of our ball bearing 114, the Inventors used analog data polling to monitor the voltage on the pins. However, digital polling may be preferred for some practical applications.

In the firmware checked by the Inventors, the angle counter was set to 0 on the ball upon initiation. The firmware samples the analog pins periodically and detects the contact between the side ring/s 23 a, 23b and the outer ring 22, the contact being made by a ball closing the circuit. We use a sequence of input samples to determine the rotation angle and the angular speed.

We use T) to describe the state of pin i e [0,1] at time T, when {H,L} represent High/Low. For example, ( o , T) means Pin 0 is High at time T, and the notation describes the state of both pins at a given time T, thus describing the whole system. Using this notation, we can describe clockwise rotation with the following series (by switching the states of the two pins, we describe counterclockwise rotation): contact with contact with contact with

pin 0 both pins pin 1

The firmware running on the Arduino polls the state of the pins and attempts to find a series as described above. The description will be further supported by Fig. 7.

Arduino' s analog resolution is 1024, with the values [0: 1024] representing voltage values of 0-5V. For our purposes, anything in the lower half of the resolution ([0:512] will be taken as low, and the rest of the values will be high. The program samples the inputs once every 5ms and averages the reading from the last 10 samples, in order to reduce noise. Each instance of the described series indicates 1/4 turn. We set the orientation such that clockwise rotation is counted as (+1), and counterclockwise as (- 1). The resulting sum is the number of 1/4 turns made by the ball bearing, which is the data output to the serial port. To indicate the result, the Grasshopper software may use this output to rotate the ball bearing model (Fig. 6b) and display the angle of rotation. For example, the angle can be displayed in the displaying, upper square box of the Grasshopper's functional diagram which is schematically shown in Fig. 6c. In our example, the displaying box may show the rotation angle "-22.5", which is the result of calculation performed by the Grasshopper. The remaining boxes of the Grasshoper diagram, from left to right, are responsible for receiving data from Arduino to a computer port, processing and multiplying the Arduino result by the number of 1/4 turns, thus arriving to the mentioned rotation angle which is then displayed.

In a practical embodiment, displaying means may be designed differently though be installed outside the ball bearing.

Fig. 7 shows, one under another, exemplary voltage outputs measured by two Arduino pins (Pin 0, Pin 1), over 100 samples taken with a 75ms sampling interval. The gray color key represents logic state of the pins. Low/low value on the pins is associated with the darkest shade of gray color, and high/high value on the pins is associated with the lightest shade of gray color in the drawing. For the electrical output, we note a tradeoff of reliability versus stability. As the angular speed increases, a higher sampling frequency is required to catch the voltage transitions. However, the greater sampling rate introduces an increasing amount of noise, which can be reduced with better surface contact, as noted in Design Process and Constraints at the end of the description. Figs. 7 shows the voltage output for both pins for different speeds of rotation over a few seconds and a complete turn, with a sampling rate of 13.333 Hz.

Based on the described graphs, and having for example, the following serie:

<(P ₀ ^H ,0),(Pi ^L ,0)>

<(Po ^L ,l),(Pi ^L ,l)>

<{P _Q ^L ,2 {P _l ^H ,2)>

<(P ₀ ^H ,3),(Pi ^H ,3)>

<(P ₀ ^H ,4),(Pi ^H ,4)>

<(P ₀ ^H ,5),(Pi ^H ,5)>

<(Po ^H ,6),(Pi ^H ,6)>

this would indicate one quarter of a clockwise rotation that takes 7 sampling cycles. (every 75ms for the given sampling rate of 13.33Hz).

Hence in this case, the angular velocity can be calculated to be +175 deg/s, or clockwise rotation with frequency 0.47Hz.

Figs. 8a, b show the Hybrid Ball Bearing Performance evaluation. FEM simulation of torque (500KNm) was applied to the inner ring 24, aligned with the ball bearing rotation plane, tested on our new, ball bearing switch design 114 and compared to a standard design 19. Darker colors represent risk (danger) to structural integrity. The FEM simulation was used to evaluate the new design 114. We simulated a torque on the inner ring, aligned with the ball bearing rotation plane. In Fig. 8a, we present the results for our ball bearing switch 114, being manufactured by 3D printing. Fig. 8b shows results obtained for a similar, but more traditional design with a unified outer ring (rather than separate side and outer rings).

The two simulations have similar results: i.e., the new design does not introduce a significant risk caused by static torque. Nevertheless, manual operation of the ball suggests a friction problem, as the rotation of the inner part is not smooth. This is a direct result of the lower accuracy of the 3D printed process compared to the professional standards of ball bearings, and can be improved by accurate post- machining.

While the above example relied on a common ball bearing design, the proposed solution (ball bearings with an integrated sensor) will also fit alternative ball bearings. Figs. 9a-9b show an exemplary design of the 3D printed voltage divider gear 100, using the conductivity/resistance of the nylon-carbon SLS enclosure being a basis of track 101. The track 101 is a variable resister created by a combination of conductive materials with different conductivity. Sensor 10 is actually active at the place of contact between track 101 and wheel 102 of the gear 100.

In essence, the gear's wheel 102 moving on the track 101 functions as a

potentiometer— by changing the resistance of the circuit as it moves on the track, it also changes the voltage on the wheel. The track 101 comprises repeated sequences of three resistors (R10, R20, R30) connected in series; this design creates voltage dividers on the track, with a different voltage value for every position (see Fig 9c). Since the shape of our track resistor is complex and the current flows along many paths, it is hard to calculate the resistance numerically. Therefore, the resistance and voltage were determined empirically from measurements. Since the resistance values vary between sequences, the expected voltage levels vary as well. As the variance is bounded by 0.25V, we associate ranges of that size to each position.

The wheel 102 itself is connected to an analog pin (let it be via input pin 103) on the Arduino board ( i.e. the processing unit, not shown), which reads the outgoing voltage from the circuit. Arduino is connected to pins: input pin 103, power pin 5V and Ground pin ( power and ground pins may be poles of a battery). The firmware routinely samples the voltage at the input pin 103 to determine the position of the wheel 102 on the track 101 as it rests between two of the track teeth. The teeth are created by separate teeth systems 104, 105, etc. which are connected (with a mutual shift) to the track resistor. The teeth systems may be 3D printed one on another, thus forming the track. Since the track provides different resistance values, the level of voltage on the input pin (103) readings can fall into four different ranges, each corresponding to a position on the track. We assume that the starting position of the wheel 102 is at the first series of resistors. Between every fourth and fifth tooth on the track, the resistance reverts from 5V to 0V, beginning a new sequence. In order to prevent the gear wheel from shorting the 5V pin of the Arduino when moving through this position, a small resistor R40 (of about 10 Ohm) buffers between the Arduino' s ground pin and its 5V pin.

The firmware samples the voltage on the analog input every 2ms, and provides a reading that averages the values of the previous five samples. The value of the reading is translated to a location (index) on the track by a lookup table, and then output to the serial port. Grasshopper software (not shown in this Figures 9) reads this value and converts it to angle and distance in order to rotate and translate the gear model to its corresponding location on the track model. Other processing and indication means may be provided.

Figs. 10a and 10b show how the Hybrid Gear Performance was evaluated. FEM simulation of torque (lOOKNm) applied to the gear wheel, aligned with the rotation plane, was tested on the proposed integrated design 100 (Fig. 10a) and compared to a standard design 109 (Fig. 10b). Darker shades of the grey color represent risk (danger) to structural integrity. As with the ball bearing, a FEM simulation of Fig. 10 supplies initial structural analysis of the gear performance, simulating torque applied to the wheel. Here, the exemplary embodiment of the new design, with thin teeth in the track, seem to have fails significantly more often than the traditional design, which has a unified linear gear instead of split teeth. In extreme conditions, the wheel of the traditional design bends a little, while our modified linear gear deforms significantly due to the weak connection of each tooth to its base. This negative effect can be reduced by using wider teeth that are more strongly connected to their bases and/or by using a side support to the track.

Fig. 11 presents voltage measurements of the gear wheel transitioning between the teeth on the track, taken from three different sets of teeth ( first four teeth at the left hand side and last four teeth at the right hand side of the drawing) . When the wheel is held steady between two teeth on the track, the sampled voltage varies by

approximately 0.025V, (at 50HZ). Therefore, a narrow average (only a few samples before and after) is enough for a reliable estimation of the gear's position, unlike the results from the ball bearing. This has a direct effect on the sensors' response time. The smaller the sampling intervals and number of samples for which it averages the values, the more sensitive it is to rapid changes.

As the resistance values are not identical between the resistor sequences, the voltage readings obtained are not identical either. Since the firmware is unaware of the existence of sequences, this necessitates a wider window of accepted values that can be mapped to each position. The size of the windows may be different for each position. Fig. 11 shows the voltage values distribution for the three different positions (a), (b), (c), each for 49 samples. Lookup tables may be built for obtaining required results.

The shades in Fig. 11 differentiate between the teeth in a sequence - each shade of gray corresponds to a different tooth (and hence a different vaultage level).

Figs. 12a, 12b show an exemplary design of the 3D-printed varying capacitance hinge 112 ( incorporating the sensor 12 being a capacitor). Fig. 12c shows an analog circuit 112 Of the hinge which uses the improved dielectric constant of a nylon-glass SLS (3D printing technique) insulator cylinder 113.

Capacitance normally depends on the dimensions and design of the device's terminals, the distance between them, and the dielectric constant of an insulator. At the present stage, for the printed hybrid elements proposed in this application, the Inventors used bronze printing for the conductive parts of the hinge. For the insulator, NyTek™ 1200 GF SLS (nylon 12 and glass) was selected. This material has a dielectric constant of 6.3 (where nylon 12 has only around 3 [23]), due to the glass particles. This combination significantly improved the capacitance of the proposed hinge, and thus its angular resolution.

The analogous electric circuit 112' represents the hinge sensor 12 as part of an Arduino controller circuit (illustrated by its inner capacitance 23) . The Arduino may be located inside the hinge 112. Pins 0 and pin 1 are shown schematically, they may be poles of a battery. The microcontroller is shown as 13.

Exemplary calculation of the hinge opening angle based on the analog circuit of Fig. 12c will be described below, with further reference to Fig. 14.

Figures 12d to 12f comprise the following images:

Fig. 12d shows a virtual model 112" of the hinge 112. It looks similar to the real hinge. The virtual model may be rendered using a VRay program.

Fig. 12e shows a 3D-printed hinge system 112, 12 (The capacitor 12 is formed inside 112). Wires schematically illustrate that signals from the capacitor 12 are transferred to a chip 13 ( for example, a schematically shown Arduino

microcontroller) which serves for processing and displaying the signals. Relevant ports of Arduino are not shown in this drawing. In practice, 13 may be integrated in the hinge 112.

Fig. 12f illustrates an operation scenario. A change in the hinge's 112 opening angle (Step 1) changes capacitance of the integrated capacitor 12 (Step 2) . Step 3: an Arduino microcontroller measures the resulting capacitance; Arduino's specific inputs are not shown. Steps 4 and 5 show how an external processing and displaying means may look: a Grasshopper script obtains output data from the microcontroller 13 and uses it (Step 5) to control the virtual model 112", mirroring the physical hinge 112. Boxes of the Grasshopper script diagram, from left to right, are responsible for receiving the Arduino results, and calculating the hinge angle using the measured capacitance. The resulting value of the hinge angle may be displayed by the Grasshopper (Step 4) and shown visually by the virtual model 112" (Step 5).

Figs. 13a and 13b illustrate performance evaluation of an exemplary proposed hybrid hinge 112 . Fig. 13a presents a FEM simulation of force applied to the exemplary hinge (10KN, pushing apart its two terminals), tested on the proposed design. Fig. 13a can be compared to Fig. 13b built similarly for a standard hinge design 129. Darker shades represent risk (danger) to structural integrity.

Since a significant percentage of the hinge's bearing is used for the variable capacitor (instead of operating as a close reinforced rotating axis), it somehow weakens the structural performance of the device, as seen in the FEM simulation (Fig. 13a). The tradeoff between the strength and capacitance of the device is obvious. Future development of AM materials with a higher dielectric constant will enable major improvements, allowing a reduction in the terminals' length. The capacitance measurement obtained from the hinge while it holds at a steady angle fluctuates by approximately lpF. The relation of capacitance to angle is not linear. Rather, as the angle decreases, the change in capacitance becomes less significant. Fig.14 (below) shows the samples taken over 15 seconds at 45, 90, and 180 degrees.

Fig. 14 is a diagram of exemplary capacitance values of the hinge measured by the Arduino as a function of the hinge's opening angle. The continuous values were

(linearly) interpolated from three data points (45, 90 and 180 degrees). The dark color area M represents the mean and standard deviation around them, where most of the data is found.

The capacitance of an exemplary hybrid hinge ranges from 5pF to 22pF. To get a reliable measurement for these values, the Inventors took advantage of the Arduino's inner capacitance 23 (please refer to Fig. 12c) The Arduino' s analog pin 1 acts as a second capacitor with a known value. For the Arduino UNO boards we use, this value is approximately 30pF [20]. Another capacitor is connected in series to the capacitor under test. The inner capacitor may be charged or discharged by changing the output to high or low, respectively. As both capacitors are connected in series, raising the pin to 5V causes current to flow through both. Once the voltage between them settles close to its final value (approximately 30ns), it can be sampled and used to determine the capacitance of the unknown capacitor. In stable state C\ = VoutC2/( urVout) ^wnere C ₂ =23pF, ¼ _n =5V and C\ is our unknown capacitor, (wherein C2 is the Arduino inner capacitance 23).

The firmware charges the capacitors by setting the output Arduino pin to high. It sets the input Arduino pin to input mode and samples the voltage between the two capacitors. The capacitance is deduced from the sample using the equation described above. The angle of the hinge is then derived from the capacitance with a third-degree polynomial, obtained for example by using Matlab's polyfit on 20 capacitance samples from one cycle of opening the hinge from 0 to 180 degrees.

For angle A and capacitance c the relation is given by A{c) = -0.0189c 3 +0.7265c 2 - 14.5779c+160.3188. After calculating the angle, the firmware sets the output pin to low, and the input pin to output mode in order to discharge the capacitors before the next measurement cycle, and waits 300ms for the system to stabilize. The wait time, greater than needed to discharge, is a safety measure to avoid starting the cycle with a charged capacitor, which could damage the microcontroller (the processor inside the Arduino).

Design Process and Constraints

The above presented embodiments of the hybrid elements rely on traditional (standard) design and fabrication tools. There is a good possibility of integration of the presently proposed technical approach of hybridization within an existing design-flow, rather than suggesting a new process. In case of using the 3D manufacturing, the design process, limitations and constraints of the proposed hybrid elements may depend on those of the selected 3D printing technology. The scale and resolution of the hybrid elements will then be bounded only by the fabrication process. For example, as the resolution of the ball bearing is determined by the number of pins embedded in the outer ring, the designer can decide to add more pins if space allows.

Alternatively, a shorter distance between the hinge terminals can improve its capacitance. However, this distance is a factor of the 3D-printed dielectric, and with current SLS technologies, wall thickness cannot be thinner than 0.8mm.

Generally speaking, the 3D (AM) printing process presently falls short compared to the accuracy of traditional machining, and AM elements of the proposed new hybrid elements may lack the operational smoothness of common machine elements. Until the accuracy of AM improves, this can be solved by post-machining the elements via milling, lathing, drilling, etc., as is already done for high-end DMLS (an additive manufacturing technique) parts. Additionally, it has been noted by the Inventors that unstable electronic behavior caused by the conductivity of human skin affects the sensors. For real-world applications of the proposed hybrid elements, it is recommended that such hybrid elements be insulated.

Implications for the Design of Potential Applications

Today, digital fabrication technologies contribute to a growing portfolio of new designs, interactions and technical solutions. Many new interactive scenarios require compact sensing solutions to control and improved performance. Additionally, many applications need small mechanical and sensorial solutions to improve their designs and lower their cost while merging the physical with the virtual. Here, we review potential applications for the proposed Hybrid elements, considering the different principles we presented and different production costs.

Professional, high-end hybrid solutions

Considering the high production costs of DMLS, we believe the main professional application for Steel-Sense is in custom, one-off solutions that require unique designs. As the main applications of DMLS technologies are already in producing unique one- offs for special needs [15], we hope our work will inspire designers and engineers to reconsider the designs of these and other hybrid-printed parts, introducing entirely new possibilities for designing interactive machines. For example, the ball bearing demonstrates a seamless integration principle: without affecting the mechanical properties of the bearing structure, we augment the element with new sensorial capabilities. Such a design could be ideal for high-end, professional mountain or road bicycles. As these bicycles use expensive fabrication technologies and composite materials to gain improved performance, the high cost of DMLS may not be a significant barrier for this application. A titanium DMLS ball bearing could sense wheel movement very accurately, without the need to attach external sensing devices that can add weight, impact the aerodynamic design of the bicycles, and be easily damaged if not fully enclosed. Moreover, such a ball bearing could be custom designed to fit unique requests, integrating it as part of a wider in-wheel system. By tracking both wheels in this way, riders, coaches, and designers could collect valuable information and analyze it to improve performance.

3D-printed custom mechatronics The Hybrid elements contribute a new design principle, showing how standard 3D printing materials can be used to implement capacitors and resistors: a 3D-printed nylon-carbon composite can function as a resistor, and a nylon-glass composite as a dialectic. Together with 3D-printed conductors and insulators, these enable the design of complicated forms and structures that can implement capacitive sensors, voltage dividers, varying resistors and capacitors, and more. While we presented a simple gear-voltage divider that can ease the integration of sensing within space-tight 3D-printed gears, we believe the potential here is much wider. Thus, we will explore it farther in our future work. One example is in developing fully interactive, 3D-printed mechatronics, or 3D-printed custom transmitter-receiver devices. Using one of the less expensive options for 3D printing metals would keep costs low, making these applications relevant to many DIY( "Do It Yourself) projects.

The shift from virtual to physical in HCI (Human Computer Interaction) encouraged researchers to investigate different designs and scenarios for physical interactive prototypes [8], many of them made using AM [19]. Haptic input devices [5] harness physical degrees of freedom for sensing, with a virtual model that reacts to physical action. As these haptic devices contain bearings and hinges, this is a good use case for considering various capacitor solutions. Moreover, while we have presented a varying capacitor hinge, a similar concept can be applied to a telescopic arm, using one of the cheaper metal 3D printing options. Together, they would enable easy DIY design and rapid prototyping of custom haptic scanners, relying on angular and linear degrees of freedom, as an example of 3D printed mechatronics.

Mass -production of hybrid elements (machine elements) Implications of hybrid elements go beyond the AM realm. A direct example relies on our pressure sensor screw. While a screw is a simple element, many people do not use it properly. We envision our 3D-printed design evolving into a mass-produced smart screw product, rather than a solely custom design solution. For example, if a user drives a screw too hard, it may crack wooden surfaces; in a cement plaster wall, over-screwing can destroy the threads of the screw holes. While a simple application inside a smart screwdriver can solve these problems, we believe such a solution may also lead to broader applications. A screw element that can report on its own pressure through a screwdriver agent invites us to conceptualize new opportunities. Just as recent developments in computer graphics seek ways to assist in design, construction and assembly of furniture [2, 16], intelligent construction elements such as screws can virtually mirror the building process and supply real-time instructions and alarms in potentially dangerous situations.

While the invention has been described and illustrated with reference to specific embodiments and applications, it should be appreciated that other implementations of the proposed principle may be proposed and should be understood as part of the invention, whenever defined by the clams which follow.

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