FORCE / TORQUE SENSOR WITH INSTRUMENTATION ON FEWER THAN FOUR MOUNTING SURFACES

Abstract

Force / torque sensor (10), comprising: a tool adapter plate (WAP), wherein the WAP (12) is configured to be connected to a first object: a mounting adapter plate (MAP) wherein the MAP (14) is configured to be connected to a second object; one or more deformable supports (16) which connect the WAP (12) to the MAP (14); a first pair of deformation measuring elements (1-6) attached only to one side of each support, wherein the deformation measuring elements (1-6) are spaced apart on opposite sides from a neutral axis (18) of the support (16) and are configured to convert tensile and compressive forces on the surface of one side of the support (16), which are caused by a deformation of the support (16), into electrical signals; and a measuring circuit which is designed to measure, in response to electrical signals from all deformation measuring elements (1-6), the direction and magnitude of the force and torque between the first and second objects; and a relief cut (34), parallel to the upper surface, at a distance from the upper surface which is not greater than the depth of the blind recess, through the ring-shaped body (14) and the supports (16), but not through the central area (12), wherein the relief cut defines a base to which the central area (12), but not the ring-shaped element (14) and the supports (16) are connected, and leaving the ring-shaped element (14) connected to the central area (12) only by the support (16).

Description

AREA OF INVENTION

[0001] The present invention relates generally to a force / torque sensor for robot applications, and in particular to a compact force / torque sensor comprising deformation measuring elements or strain measuring elements that are attached to only one surface of a deformable carrier. BACKGROUND

[0002] Robotics is a growing and increasingly important field in industrial, medical, scientific, and other applications. In many cases where a robot arm or a tool attached to it touches a workpiece, the force and / or torque must be precisely monitored. Accordingly, a force / torque sensor is an important component of many robotic systems.

[0003] A conventional type of force / torque sensor uses deformation sensing elements or deformation gauges to measure the deformation of small carriers connecting two mechanical parts: one attached to the robot arm and the other attached to a robot tool (or a mechanical coupling to the tool). For example, a central "central area," known in engineering as the tool adapter plate (WAP), is attached to a tool. Another body, arranged ring-shaped around and spaced from the WAP, known in engineering as the mounting adapter plate (MAP), is attached to a robot arm. The MAP and the WAP are connected to each other by a multitude of relatively thin (and therefore mechanically deformable) carriers arranged radially around the WAP—in some cases, resembling the spokes of a wheel.Relative force or torque between objects attached to the WAP and the MAP respectively attempt to move the MAP relative to the WAP, resulting in a slight deformation or bending of at least some of the beams.

[0004] Traditionally, strain gauges are attached to all four surfaces of each beam, nominally at the center of each corresponding surface. The gauges translate tensile and compressive stresses on the beam surfaces into electrical signals. As an example of their operation, consider forces in or parallel to the plane of WAP and MAP—that is, a torque in the z-direction (Tz, using the right-hand rule) or a force in the x- or y-direction (Fxy). These forces will attempt to bend at least some of the beams laterally. In this case, a strain gauge on one side of a beam will detect a compressive stress, and a gauge on the opposite side of the beam will detect a tensile stress. These gauges output strong signals with opposite polarity. Strain gauges on the top and bottom surfaces of the same beam will output very weak signals, or no signals at all.Conversely, forces attempting to move the MAP or WAP out of their common plane (Fz, Txy) generate strong and opposing output signals from the deformation measuring elements on the upper and lower support surfaces, with a small contribution from deformation measuring elements on the sides.

[0005] Once calibrated, signals from all four deformation sensors on all carriers are processed together to resolve the magnitude and direction of the relative force and / or torque between the robot arm and the tool (and thus the force / torque exerted by the tool on a workpiece). Equipping a force / torque sensor is a significant cost factor in the product, as it requires precise and highly skilled manual work. Equipping also imposes design constraints on the sensor's mechanical design, as considerable physical space is required around each of the four equipped surfaces of each carrier to inspect it and access the hand tool. These constraints become particularly restrictive with very small sensor sizes and may necessitate suboptimal sensor geometry to accommodate the setup and allow for equipment verification.Furthermore, a lengthy and complex connecting wire routing is required to transmit electrical signals from deformation measuring elements on all four surfaces of each carrier to a central processing circuit, which can increase the risk of device failure.

[0006] WO 99 / 04 235 A1 discloses a force / torque sensor comprising a central section and a rigid annular ring connected by a plurality of radial tubes. Deformation sensors are mounted on many sides of the radial tubes.

[0007] US 2005 / 0120809 A1 discloses a robot force measuring device comprising an inner plate surrounded by an outer plate, wherein the inner and outer plates are integrally connected by a plurality of deformation-detecting bending elements, generally in the form of deformation rings. Deformation-detecting devices are mounted on many sides of the deformation rings.

[0008] US 2015 / 0033875A1 discloses a sensor body comprising a generally rigid surrounding element arranged around a spaced-apart central element connected to each of two leg halves. The sensor body has deformation sensors on many sides of the bending elements.

[0009] DE 38 52 271 T2 discloses a force detector and a torque detector that use resistive elements. In particular, a detector is described that determines force and torque by stress-deformation, converts these into a change in the resistance value of the resistive elements, and thus provides an output in the form of an electrical signal.

[0010] The background section of this document is provided to place embodiments of the present invention in a technological and operational context, in order to assist the person skilled in the art in understanding their scope and benefits. Unless expressly identified as such, no statement herein is explained as prior art merely by its inclusion in the background section. SUMMARY

[0011] The following is a simplified summary of the disclosure to provide the person skilled in the art with a basic understanding. This summary is not a comprehensive overview of the disclosure and is not intended to identify key or critical elements of embodiments of the invention or to outline the scope of the invention. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as an introduction to the more detailed description that follows.

[0012] According to one or more embodiments described and claimed herein, a force / torque sensor comprises a pair of deformation sensing elements attached to only one surface of each carrier connecting a WAP and a MAP. The two deformation sensing elements are, for example, attached to the top surface on each side and spaced apart from a neutral axis of the carrier. The fact that only one access to the top carrier surface is required allows for a very compact sensor design—which, according to one embodiment, is manufactured from a single piece of metal. The single surface enables the use of automated manufacturing technologies, such as wire bonding the deformation sensing elements to contact points of a printed circuit board, surface mounting the deformation sensing elements to a flexible circuit substrate, or bonding the substrate to the carrier surface.The two deformation sensors can be connected in a quarter-bridge topology. In a configuration with three supports and six sensors, the positive and negative output signals of the six deformation sensors (due to the transmission of either compressive or tensile forces) sum up in five of the six force / torque axes (Fx, Fy, Fz, Tx, Ty, Tz); known force / torque sensor designs only achieve this for four of the six axes. This facilitates the mathematical cancellation of common-mode signal components, such as temperature drift. In one embodiment, another pair of deformation sensors is mounted on the same side of the support, and the four deformation sensors are wired in a half-bridge topology. In another embodiment, a second pair of deformation sensors is mounted on the opposite side of the support, and the four sensors are wired in a half-bridge topology.The half-bridge topologies achieve electrical elimination of common-mode signal components. In one embodiment, the axis of the six that does not sum to zero can be selected by inverting the excitation potential. In another embodiment, a seventh deformation measuring element is connected to an unstressed element of the sensor to provide a signal for temperature calibration.

[0013] One embodiment relates to a force / torque sensor. The sensor includes a tool adapter plate (WAP) that can be connected to a first object and a mounting adapter plate (MAP) that can be connected to a second object. The sensor also includes one or more deformable supports that connect the WAP to the MAP. A first pair of deformation sensing elements is attached to only one side of each support. The deformation sensing elements are located on opposite sides of a neutral axis of the support and are spaced from it, and they are configured to convert tensile and compressive forces on the surface of one side of the support, caused by the deformation of the support, into electrical signals.The sensor further comprises a measuring circuit which, in response to electrical signals from all deformation measuring elements, can measure the direction and magnitude of the force and torque between the first and second objects. The sensor further comprises a relief cut, parallel to the upper surface, at a distance from the upper surface not greater than the depth of the blind recess, through the annular body and the supports, but not through the central area, wherein the relief cut defines a base to which the central area, but not the annular element and the supports, is connected, and the annular element remains connected to the central area only by the support.

[0014] Another embodiment relates to a method for manufacturing a one-piece force / torque sensor from a disk-shaped metal material. The material has coplanar upper and lower surfaces, generally circular in shape, with a thickness between the upper and lower surfaces. Blind recesses are milled into and transversely to the upper surface. The blind recesses extend in depth to a depth less than the thickness of the material. The blind recesses define a generally circular central region in the middle of the material, an annular body surrounding the central region, and one or more supports arranged radially around the central region, connecting the central region to the annular body. The upper surfaces of the central region and the supports are milled to be lower than the upper surface of the annular body.A relief cut is milled parallel to the upper surface at a distance from the upper surface no greater than the depth of the blind recesses. The relief cut is milled through the annular body and the supports, but not through the central area. The relief cut defines a base to which the central area, but not the annular body and the supports, is connected, so that the annular body remains connected to the central area only via the supports. A pair of deformation sensors is mounted only on the top surface of each support on opposite sides of a neutral axis of the support and spaced from it. The deformation sensors are configured to convert tensile and compressive forces on the surface of the top of the support, caused by deformation of the support, into electrical signals.The deformation measuring elements on each carrier are electrically connected to a processing circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will now be described in more detail below with reference to the accompanying drawings, which show embodiments of the invention. However, this invention should not be interpreted as being limited to the embodiments shown herein. Rather, these embodiments are provided so that this disclosure is thorough and complete and fully conveys the scope of the invention to those skilled in the field. Identical numbers refer to identical elements throughout. Fig. Figure 1 is a top view of a force / torque sensor. Fig. Figure 2 is an enlarged view of a carrier of the force / torque sensor. Fig. 1. Fig.Figure 3 is a sectional view and a functional circuit diagram of a quarter-bridge circuit topology of deformation measuring elements on a beam. Fig. Figures 4A to 4G are perspective views showing successive steps in the manufacture of a one-piece force / torque sensor. Fig. Figure 5 is a flowchart of a process for manufacturing a one-piece force / torque sensor. Fig. Figure 6 is a perspective view of the wire connection of deformation measuring elements on a PCB. Fig. Figure 7 is a perspective view of deformation measuring elements surface-mounted on a flexible circuit substrate. Fig. Figure 8 is a perspective sectional view of a force / torque sensor showing an unloaded element for mounting a temperature-compensating deformation measuring element. Fig.Figure 9 is a sectional view and functional circuit diagram of an X-connection half-bridge circuit topology of deformation measuring elements on a support. Fig. Figure 10 is a sectional view and functional circuit diagram of a half-bridge circuit topology with inverted excitation polarity. Fig. Figure 11 is a top view of a force / torque sensor with two pairs of deformation measuring elements attached only to the top surface of each support. Fig. Figure 12 is an enlarged view of a carrier of the force / torque sensor made of Fig. 9 with a superimposed functional circuit scheme representing a half-bridge topology. DETAILED DESCRIPTION

[0016] For the sake of simplicity and clarity, the present invention is described primarily with reference to an exemplary embodiment. Numerous specific details are set forth in the following description to facilitate a thorough understanding of the present invention. However, it is clear to the person skilled in the art that the present invention can be carried out without being limited to these specific details. Well-known methods and structures have not been described in detail in this description in order to avoid unnecessarily obscuring the present invention. Inventive deformation measuring element placement

[0017] Fig.Figure 1 shows a top view of an embodiment of a force / torque sensor 10 according to an embodiment of the present invention. A WAP 12 is connected to a MAP 14 by three supports 16a, 16b, 16c. In the illustrated embodiment, each support 16 is directly connected to the WAP 12 and is connected to the MAP 14 by bending elements 17 that support the deformation of the supports 16 under mechanical load. The WAP 12 is configured such that it can be accessed via a through-hole 30 or through threaded holes in the underside of the sensor 10 (not shown in the illustration). Fig. (1 shown) is connected to a first object, for example, a robot tool. The MAP 14 is configured to be connected to a second object, for example, a robot arm, via a plurality of mounting openings 32. Although it is not clear from this view, the WAP 12 and the MAP 14 are connected only by the supports 16.

[0018] Deformation measuring elements 1-6 are attached to (only) the upper surface of each support 16. For reference in later discussion, measuring elements 1 and 2 are attached to support 16a; measuring elements 3 and 4 are attached to support 16b, and measuring elements 5 and 6 are attached to support 16c. Fig. Figure 1 also shows two axes of a Cartesian three-dimensional reference coordinate system (z-direction extends out of the figure) which are used to uniquely identify forces and torques in the following disclosure.

[0019] Although this in Fig.Not shown in Figure 1, the force / torque sensor 10 also includes a processing circuit configured to receive electrical signals from each deformation measuring element 1-6 and to process the signals in order to resolve the magnitude and direction of the force(s) and torque(s) exerted between the MAP 14 and the WAP 12. Such processing circuits may, for example, involve a microprocessor coupled with a memory configured to store program code and sensor data.

[0020] Fig.Figure 2 is an enlarged view of a beam 16a deforming relative to the MAP 14 due to a force F applied to the WAP 12. This force deforms the beam 16a slightly to the left (the figure is not to scale). A compressive force is induced on the left side of the beam 16a, and a tensile force is induced on the right side. In the prior art, deformation measuring elements attached to these surfaces would generate strong signals of opposite polarity, from which the deformation, and thus the applied force F, could be determined. However, the two sides of the upper surface of the beam 16a also experience compressive and tensile stresses of a magnitude that increases with distance from a neutral axis 18.The neutral axis 18 is the line that generally extends downwards from the center of the upper surface of the support 16a, whereby the compressive stress occurring on the left side of the support 16a becomes a tensile stress on the right side. Accordingly, the support 16a experiences no stress at the neutral axis 18.

[0021] According to embodiments of the present invention, a pair of deformation measuring elements 1, 2 is attached only to the upper surface of the support 16a. The deformation measuring elements 1, 2 are arranged on each side of the neutral axis 18 and spaced apart from it. Differential signals, such as signals with opposite polarities, from the deformation measuring elements 1, 2 indicate a bending of the support 16a in the plane of the upper surface (i.e., Tz, Fxy). Common-mode signals (same polarity) would indicate a bending of the support 16a in the z-direction (i.e., caused by Fz, Txy).

[0022] In one embodiment, the pair of deformation measuring elements on each support 16 is wired in a quarter-bridge topology, using two fixed resistors, which in Fig. 3 is shown. The six deformation measuring elements 1-6, which are as shown in Fig. 1 shown on the supports 16a-c, generate with reference to the Cartesian coordinate system according to Fig. 1. Taking into account the six applied forces and torques, the following signals are used. In the following table, a strong tensile force is denoted by "T", a weak tensile force by "t", a strong compressive force by "C", and a weak compressive force by "c". Table 1: Deformation measuring element output signals at specific forces / torques Force X Force Y Force Z Torque X Torque Y Torque Z Measuring device 1 C No T T No T Measuring device 2 T No T T No C Measuring device 3 t T T c C T Measuring device 4 c C T C C C Measuring device 5 t C T C T T Measuring device 6 c T T c T C

[0023] A review of Table 1 reveals that the signals generated under each load condition follow distinct patterns and can therefore be resolved into forces and torques using a known calibration matrix method. One-piece sensor manufacturing and automated wiring options

[0024] The need for access to only one support surface offers significant advantages in the manufacturing of the mechanical components of a force / torque sensor. In one embodiment, the entire sensor is manufactured from a single piece of metal. This eliminates the conventional separate MAP and WAP components and their associated mechanical interfaces, thereby reducing the number of parts and the required assembly steps. Additionally, the one-piece design is more compact than known force / torque sensors operating over the same force / torque range, due to the need to access only the upper surface of the support 16 to mount the deformation measuring elements 1-6. Furthermore, the one-piece design offers very high rigidity and eliminates the risk of slippage, as there are no screw connections.

[0025] A one-piece force / torque sensor, made of aluminum for example, is used in the Fig. 4F and Fig. 4G is shown. The sensor 10 includes a through-hole 30 through the WAP section 12 and the mounting features 32 on the MAP section 14. It can be manufactured without electrical discharge machining (EDM) using end mills not less than 3 / 32 inch in diameter, according to a method described with reference to the Fig. 4A-G is shown.

[0026] Fig. Figure 4A shows the starting point: a disc-shaped piece of metal material with parallel, generally circular, top and bottom surfaces and a thickness in between. As shown in Figure 4B, blind recesses are milled to form the supports 16 and the bending elements 17, which immediately begin to form a central area that becomes the WAP 12, separated from an annular body that becomes the MAP 14.

[0027] Fig. Figure 4C shows that the upper surface of the WAP 12, the supports 16, and the bending elements 17 are milled below the upper surface of the MAP 14. This creates a raised mounting surface for the MAP side 14 of the sensor 10. A non-structural cover can be installed later to protect the supports 16 and the electronics from dust and mechanical damage. If a through-hole 30 is required for mounting or for the passage of electrical or fluid lines, it is drilled through the WAP 12, as shown in Figure 4D. Fig. Figure 4E shows the MAP 14 mounting openings 32, which are drilled and threaded. In one embodiment, for further cost reduction, the mounting openings 32 have an identical pattern on the MAP and WAP sides and are drilled and threaded in a single step.

[0028] Next, a relief cut 34 is made on the side of sensor 10, as shown in Fig. 4F is shown. The relief cut 34 is no lower (measured from the upper surface of the MAP 14) than the depth of the blind recesses milled to form the beams 16 and bending elements 17. Accordingly, the relief cut 34 separates the MAP 14 from any other mechanical connection with the WAP 12, apart from the connection via the beams 16. In other words, and as is best seen in the sectional view of Fig. As shown in Figure 4G, while the WAP is connected to the "base" of the sensor under the relief cut 34, this is not the case for the MAP 14 – rather, it "slides" freely from the sensor 10, which is connected to the TAP 12 only via the supports 16 and bending elements 17. In the finished product, the gap 34 can be filled with a compressible foam seal to prevent the ingress of dust.

[0029] Fig.Figure 4F shows the finished body of the force / torque sensor 10 in a fully perspective view. Fig. Figure 4G shows the finished sensor body in a cutaway perspective view. Various embodiments may include additional features to protect the electronics, provide wiring and access to LED indicators, and the like. In one embodiment, a section of the WAP 12 is milled to largely remove all mechanical stresses, thereby creating a mounting location for a temperature compensation measuring device, which is discussed in more detail herein.

[0030] Fig.Figure 5 shows the steps of a method 100 for manufacturing a one-piece force / torque sensor 10 from a disk-shaped metal material. The material has coplanar top and bottom surfaces, generally circular in shape, and a thickness between the top and bottom surfaces. First, blind recesses are milled into and across the top surface. The blind recesses extend in depth to a depth less than the thickness of the material. They define a generally circular central region 12 in the center of the sensor, an annular body 14 surrounding the central region, and a plurality of supports 16 arranged radially around the central region 12, connecting the central region 12 and the annular body 14 (Block 102). The top surfaces of the central region 12 and the supports 16 are milled to be lower than the top surface of the annular body 14 (Block 104).

[0031] A relief cut 34 is milled parallel to the upper surface at a distance from the upper surface that is no greater than the depth of the blind recesses. The relief cut 34 extends through the annular body 14 and the supports 16, but not through the central area 12. The relief cut 34 defines a base to which the central area 12 is connected, but the annular body 14 and the supports 16 are not. This leaves the annular body 14, which is connected to the central area 12, connected only by the supports 16 (block 106).

[0032] A pair of deformation measuring elements 1-6 is attached only to the top surface of each support 16. The two deformation measuring elements 1-6 on each support 16 are arranged on opposite sides of and spaced apart from a neutral axis 18 of the support 16. The deformation measuring elements 1-6 are configured to convert tensile and compressive forces on the surface of the top of the support 16, caused by deformation of the support 16, into electrical signals (Block 108). The deformation measuring element 1-6 on each support 16 is electrically connected to a processing circuit (Block 110).

[0033] In one embodiment, the blind recesses further define bending elements 17 transverse to each support 16, which are arranged at the distal end of the support 16 from the central area 12. The bending elements 17 are connected to the annular body 14. As additional steps, a through-hole 30 can be drilled through the central area 12 for attachment to a tool or to facilitate the passage of electrical wires or fluid lines; and a plurality of mounting holes 32 can be drilled and threaded in the annular body 14 for mounting on a robot arm. Additional features can be formed, such as passages for wiring and LEDs, as well as an unloaded element 37 (see Fig. 8) for attaching a temperature-compensating deformation measuring element.

[0034] The force / torque sensor 10 of the Fig.The 4A-G is more compact and requires fewer parts to be manufactured and assembled than known force / torque sensors. Arranging the deformation measuring elements 1-6 only on the upper surface of the carriers 16 also allows for shorter wire runs, simple sight lines, and access to hand tools, as well as fewer geometric restrictions compared to the prior art. Furthermore, the inventive arrangement of all deformation measuring elements 1-6 on the upper surfaces of the carriers 16 enables additional cost-saving manufacturing possibilities.

[0035] In one embodiment, which is in Fig.As shown in Figure 6, the measuring instruments 1-6 are attached to the carriers 16 without bond wires using conventional means (e.g., manually with epoxy resin). A printed circuit board (PCB) 20 with wire contact points 24 is glued to the surface of the WAP 12. The electrical connections 22 are then formed directly between the measuring instruments 1-6 and the PCB wire contact points 24 using a wire bonding machine, thus eliminating all manual handling of the bond wires. As is known from electronics, automated wire bonding is faster, more accurate, and cheaper than manual wiring.

[0036] In another embodiment, as in Fig.As shown in Figure 7, the deformation measuring elements 1-6 with solder contacts are mounted face down on SMD (Surface Mount Device) contacts on a flexible circuit substrate 26, for example, a polyimide film. The flexible substrate 26 is bonded to the body of the sensor 10, for example, via the WAP 12, and has tabs that extend at least partially onto the upper surface of each carrier 16. The measuring elements 1-6 are placed on the flexible substrate 26 along with all other circuit components by a pick-and-place machine and melted to fuse them in place. The SMD contacts are connected on the substrate 26 by pre-formed conductor tracks 28, for example, made of copper. This eliminates all cable wiring at the cost of a reduced signal magnitude (e.g., a lower signal-to-noise ratio) due to the bending of the polyimide material.In this embodiment, both the manual fastening and the wiring of the deformation measuring elements 1-6 are eliminated, resulting in cost reduction and increased quality, uniformity and production speed. zero-sum coefficients

[0037] In the prior art concerning force / torque sensors with three beams, there are two sets of three half-bridge topologies of deformation measuring elements—the top / bottom and the left / right measuring elements—attached to each beam. Each of these sets is largely separated from the others with respect to the external loads to which it responds: the left / right set responds to horizontal beam bending (induced by Tz and Fxy), while the top / bottom set responds to vertical bending (induced by Txy and Fz). When Fxy or Txy is applied in this arrangement, some beams bend in one direction while others bend in the opposite direction, generating signals with opposite polarity on the respective pairs of measuring elements.Because of this behavior, coefficients in a calibration matrix have different polarities for the various pairs of measurements in the equation that solves an X / Y load. In an ideal converter (without significant misalignment or spurious effects), the coefficients for these X / Y equations sum to nearly zero, since the different pairs of measurements contribute equally to the calculated output signal but are loaded in opposite directions. When the coefficients sum to zero in this way, any common-mode signals appearing on the measuring instruments are mathematically canceled out. These common-mode signals are generally temperature-induced effects that should be rejected by the system when calculating its final output signals.

[0038] Since the traditional measurement setup has two cases in which the three active measuring instruments react in the same way (Fz and Tz), these two axes cannot sum to zero and will therefore exhibit worse performance during warm-up (drift) and other temperature changes, as the unwanted common-mode signals from all measuring instruments are mixed instead of being canceled.

[0039] In contrast, embodiments of the present invention have the significant advantage that, since all (near-surface only) measuring devices respond to all types of loads, they also represent a zero sum for the Tz axis, while retaining the zero-sum advantage for X / Y load cases as in the prior art. This is because, under Tz, the sensor 10 according to the invention has six active signals of equal magnitude: three with positive polarity and three with negative polarity. Fz is the only axis that does not sum to zero, and in this case, an alternative compensation method must be used to achieve performance comparable to the other five axes. Table 2 below shows this performance characteristic for the Fig. 1. Configuration shown with the in Fig. 3 circuit topologies shown: Table 2: Measuring device output polarity under specific forces / torques carrier 16a 16a 16b 16b 16c 16c measuring device 1 2 3 4 5 6 sum Power X - + + - + - 0 Power Y + - - + 0 Power Z + + + + + + 6+ torque X + + - - - - 0 torque Y - - + + 0 torque Z + - + - + - 0

[0040] Each series, except for Fz (third series), is added to zero. In this case, all measuring instruments output a positive polarity signal. Temperature compensation

[0041] The simplest and most cost-effective implementation of surface-only measuring instruments is the use of a quarter-bridge circuit topology. The quarter-bridge topology has certain inherent disadvantages compared to the conventional half-bridge topology, which is used when two measuring instruments are present, the most important of which is a temperature-induced fault. In a half-bridge topology, signals that affect each measuring instrument equally (usually induced by temperature changes) are canceled out by their electrical arrangement, and only differential signals (induced by the expansion of one measuring instrument and the compression of the other) are present in the output signal of the half-bridge circuit.

[0042] According to some embodiments of the present invention, a temperature compensation method is used to mitigate this problem in a quarter-bridge topology. In one embodiment, a seventh deformation sensor, identical to the six active deformation sensors 1-6, is attached to a portion of the force / torque sensor 10 that does not experience any mechanical load under an applied force or torque. The signal from a seventh deformation sensor attached to this extension 37 is then affected only by temperature and not by loads, and is then mathematically removed from the signals of the other six deformation sensors 1-6 when the resolved loads are calculated to compensate for temperature drift. As in Fig.As shown in Figure 8, to achieve the smallest possible amount of mechanical coupling with the seventh measuring device, a section 35 of the force / torque sensor 10 is milled away to define a thin, cantilevered extension 37 that does not bear any mechanical load. The temperature-compensating deformation measuring element is attached to the end of the extension 37. Fig. Figure 8 additionally shows that other features can be milled out if required or desired, such as the wiring channel 33. Half-bridge topologies

[0043] In other embodiments of the present invention, both the temperature cancellation advantages of the half-bridge circuit topology and the zero-sum advantage for five of the six force / torque axes are achieved by replicating the arrangement of two deformation measuring elements on the lower surface of each support 16 as well as on the upper surface. The four measuring elements on each support 16 are then connected in an X-configuration to achieve a half-bridge circuit topology, as described in Fig. Figure 9 shows that this configuration produces the same output pattern as the quarter-bridge topology shown in Table 2 above.

[0044] When deformation sensor pairs are attached to both the upper and lower surfaces of each support 16, some of the inherent space and cost advantages of surface-only embodiments are lost—for example, a sensor 10 design must provide access to the bottom surfaces of the supports 16 to allow for equipment and wire routing. However, in applications where eliminating temperature drift is more important than the size of the sensor 10 or the manufacturing cost, these embodiments retain significant advantages over the prior art. For example, the measurement output signals in five out of six force / torque axes still sum to zero (compared to only four out of six in the prior art), and the sensor 10 design can still be more compact because access to the side surfaces of the supports 16 is not required.

[0045] In one embodiment of the half-bridge topology, the excitation polarity of one of the deformation measuring elements is reversed, as is the case in Fig. Figure 10 is shown. This has the effect of shifting the non-zero sum axis from Fz to Tz, as shown in Table 3 below: Table 3: Output polarity of a half-bridge measuring device with inverted excitation polarity carrier 16a 16a 16b 16b 16c 16c measuring device 1 2 3 4 5 6 sum Power X + + - - - - 0 Power Y - - + + 0 Power Z - + - + - + 0 torque X - + + - + - 0 torque Y - + + - 0 torque Z - - - - - - 6-

[0046] This embodiment is particularly useful in applications where Tz does not occur or is otherwise less important than an accurate measurement of Fz.

[0047] In another embodiment, where the applied forces / torques are applied for a duration longer than momentary, a circuit first establishes the excitation polarity. Fig.9 and receives a zero-sum signal for all axes other than Fz. The applied excitation voltage is then applied to the in Fig. The configuration shown in Figure 10 is switched, and a zero-sum reading is obtained for Fz, while Tz generates the non-zero-sum signals. In this way, zero-sum equations are applied to all six force / torque axes, and all common-mode signals, such as temperature-induced errors, are eliminated. This eliminates the need for an associated temperature compensation deformation sensor (and the mathematical elimination of the error) or the need to create an unstressed mounting point for the temperature compensation sensor.

[0048] The main disadvantage of embodiments of the half-bridge circuit topology described above is the need to attach deformation measuring elements to both the upper and lower surfaces of each support 16. Fig. Figure 11 shows a force / torque sensor 10 in which two deformation measuring elements are attached only to the upper surface of each support 16. As in the single-pair embodiments, the two pairs of deformation measuring elements are each attached to the upper surface of the support 16 only on each side and spaced apart from the neutral axis of the support 16. In some embodiments, a strain- or deformation-concentrating opening may be formed through the support 16 between each pair of deformation measuring elements.

[0049] In this embodiment, several bending elements 17 on each support 16 prevent significant compressive and tensile stress, while rotation at the free end of the supports 16 is largely prevented. This causes the supports 16 to deform under shear stress under all loading conditions. Thus, when electrically connected, the measuring devices behave like a Fig.As shown in Figure 12, the forces are always approximately equal, but in opposite directions (tension / compression) under all loading conditions. The mechanical construction of this embodiment has some additional complexity, but it can be manufactured using the same methods and tools as those used in the embodiment shown in Figure 12. Fig. 4A-4G were discussed, and this additionally leads to an increase in overall stiffness. Advantages

[0050] Embodiments of the present invention offer numerous advantages over known force / torque sensors. By arranging the deformation measuring elements 1-6 in splayed pairs, spaced from the neutral axis only on the upper surface of each carrier 16, it is possible to manufacture a compact force / torque sensor 10. In one embodiment, the sensor 10 can be manufactured from a single piece of metal using only conventional milling methods. The ease of access to the deformation measuring elements 1-6 allows for automated wire bonding on a printed circuit board or automated placement on a flexible substrate – in both cases, manual placement and / or wiring are eliminated.All embodiments exhibit zero-sum coefficients in five of the six force / torque axes, enabling the mathematical elimination of common-mode signals, such as those induced by temperature changes. Temperature compensation can also be applied to quarter-bridge topology embodiments by arranging a temperature-compensating deformation sensing element on an unloaded element of the sensor 10. In half-bridge topology embodiments, arranging an additional pair of deformation sensing elements on the lower surface of each carrier 16 electrically eliminates common-mode signals in the five of the six zero-sum force / torque axes. In one embodiment, the non-zero-sum axis can be modified by reversing the excitation polarity, thereby completely resolving all six axes with electrical temperature drift elimination.One embodiment allows for a half-bridge topology while retaining the advantages of surface-only deformation measuring element mounting.

[0051] Embodiments of the present invention have been presented and described such that they have three supports 16a, 16b, 16c. While three equipped supports 16 are the minimum number required to resolve a 6-axis force / torque load, in some cases more supports 16 may be desirable. More supports can, for example, add stiffness to a sensor 10 and / or provide redundancy in case the equipment on one support in the relevant area fails. In certain applications where full 6-axis force / torque resolution is not required, a sensor 10 can use two or even one support 16.

[0052] For the sake of simplicity and to provide a consistent context in which the principles and operation of force / torque sensors are discussed, the supports connecting a WAP and a MAP, both in the prior art and in embodiments of the present invention, are described herein as having four surfaces, that is, a square or rectangular cross-section. While this is a common and economical configuration, nothing in the present disclosure limits embodiments of the invention to supports with four surfaces. Those skilled in the art will readily recognize that a support can be configured with any polygonal cross-section (e.g., triangular, octagonal, etc.) or with an arcuate cross-section (e.g., circular, elliptical, oval, etc.).As used herein, the terms “a surface”, top / bottom / side / left / right surface, and the like, when applied to a beam having a cross-section other than a square or rectangular one, mean that the extent of the beam is viewed or retrieved from one of four orthogonal directions, as defined by the force / torque reference axes. Thus, for example, a pair of deformation measuring elements attached to a beam having a circular cross-section would be considered to be on the same, top “side” if both measuring elements are located within approximately ±45° of the projected central axis, projected onto the surface in the z-axis direction to produce a 0° reference line running longitudinally along the beam. The person skilled in the art can readily apply the measuring elements of the present invention to other beam shapes.

[0053] The present invention can, of course, be carried out in ways other than those specifically stated herein without deviating from the essential content of the invention. The present embodiments are to be regarded in all respects as illustrative and not as limiting, and all modifications that fall within the scope and equivalence of the appended claims are hereby included.

Claims

[1] Force / torque sensor (10), comprising: a tool adapter plate (WAP), wherein the WAP (12) is configured to be connected to a first object: a mounting adapter plate (MAP) wherein the MAP (14) is configured to be connected to a second object; one or more deformable supports (16) which connect the WAP (12) to the MAP (14); a first pair of deformation measuring elements (1-6) attached only to one side of each support, wherein the deformation measuring elements (1-6) are spaced apart on opposite sides from a neutral axis (18) of the support (16) and are configured to convert tensile and compressive forces on the surface of one side of the support (16), which are caused by a deformation of the support (16), into electrical signals; and a measuring circuit which is designed to measure, in response to electrical signals from all deformation measuring elements (1-6), the direction and magnitude of the force and torque between the first and second objects; and a relief cut (34), parallel to the upper surface, at a distance from the upper surface which is not greater than the depth of the blind recess, through the ring-shaped body (14) and the supports (16), but not through the central area (12), wherein the relief cut defines a base to which the central area (12), but not the ring-shaped element (14) and the supports (16) are connected, and leaving the ring-shaped element (14) connected to the central area (12) only by the support (16). [2] Sensor (10) according to claim 1, wherein: the first object is a robot tool or a mechanical coupling with a robot tool; and the second object is a robot arm or a mechanical coupling with a robot arm. [3] Sensor (10) according to one of claims 1-2, further comprising a strain-concentrating opening (36) through each carrier (16) between the deformation measuring elements (1-6) on one side of the carrier (16). [4] Sensor (10) according to one of claims 1-3, wherein the pair of deformation measuring elements (1-6) which are attached to a carrier (16) are electrically connected in a quarter-bridge topology with two fixed resistors (R1, R2). [5] Sensor according to one of claims 1-4, further comprising a printed circuit board (20) which includes the measuring circuit, and wherein electrical connections (22) are formed by wires from contact points (24) on the printed circuit board (20) to the deformation measuring elements (1-6). [6] Sensor (10) according to one of claims 1-5, further comprising a flexible circuit substrate (26), wherein the pair of deformation measuring elements (1-6) is surface-mounted on the flexible circuit substrate (26), and wherein at least one section of the flexible circuit substrate (26) which includes the deformation measuring elements (1-6) extends over a carrier (16) to which it is attached. [7] Sensor (10) according to any one of claims 1-6, wherein the WAP (12), the MAP (14) and the carrier (16) are all made from a single piece of metal material and form an integral unit. [8] Sensor (10) according to one of claims 1-7, further comprising a non-tensioned element (37) which is connected to one of the WAP (12) and the MAP (14), wherein the other non-connected element is not deformed in response to a force or torque between the first and second object, and which further comprises a deformation measuring element (1-6) which is attached to the non-tensioned element. [9] Sensor (10) according to one of claims 1-8, wherein the output of each deformation measuring element (1-6) has a positive or negative polarity, and wherein the sum of all output signals of all deformation measuring elements (1-6) for at least five of six force / torque axes, which are from group F x , F y , F z , T x , T y , T z The number selected is essentially zero. [10] Sensor (10) according to claim 9, wherein the sum of all output signals of all deformation measuring elements (1-6) for the F z -axis is not essentially zero. [11] Sensor (10) according to one of claims 1-10, further comprising a second pair of deformation measuring elements (1-6) which are attached to the opposite side of each support (16) from the first pair of deformation measuring elements (1-6), wherein the second pair of deformation measuring elements (1-6) is spaced apart on opposite sides from the neutral axis (18) of the support (16) and is configured to convert tensile and compressive forces caused by a deformation of the support (16) into electrical signals on the opposite surface of the support (16), and wherein the first and second pair of deformation measuring elements (1-6) are connected on each support (16) in a half-bridge topology. [12] Sensor (10) according to claim 11, wherein the sum of all output signals of all deformation measuring elements (1-6) for at least five of six force / torque axes, which are from group F x , F y , F z , T x , T y , T z are selected, is essentially zero, and wherein the one force / torque axis for which the deformation measuring element (1-6) outputs do not sum to essentially zero is changed by reversing the excitation polarity of one of the deformation measuring elements (1-6) of each support. [13] Sensor (10) according to one of claims 1-10, further comprising a second pair of deformation measuring elements (1-6) which are attached on the same side of each support (16) as the first pair of deformation measuring elements (1-6), wherein the second pair of deformation measuring elements (1-6) is spaced apart on opposite sides from the neutral axis (18) of the support (16) and is configured to convert tensile and compressive forces on the surface of the support (16) caused by deformation of the support (16) into electrical signals, and wherein the first and second pair of deformation measuring elements (1-6) are connected on each support (16) in a half-bridge topology. [14] Sensor (10) according to claim 13, further comprising a strain-concentrating opening (36) through the carrier (16) between the deformation measuring elements (1-6) of each pair. [15] Method (100) for manufacturing a one-piece force / torque sensor (10) from a disk-shaped metal material, wherein the material has coplanar upper and lower surfaces of generally circular design with a thickness between the upper and lower surfaces, wherein the method (100) comprises: Milling blind recesses in and transverse to the upper surface, wherein the blind recesses extend in depth less than the thickness of the material, and wherein these define a generally circular central area (12) in the center of the material, wherein an annular body (14) surrounds the central area and one or more supports (16) are arranged radially around the central area (12) and establish a connection between the central area (12) and the annular body (14); Milling the upper surfaces of the central area (12) and the supports (16) so that they are lower than the upper surface of the ring-shaped body (14); at a distance from the upper surface which is not greater than the depth of the blind recesses, milling a relief cut parallel to the upper surface through the annular body (14) and the supports (16), but not through the central area (12), wherein the relief cut defines a base to which the central area (12), but not the annular element (14) and the supports (16) are connected, and leaving the annular element (14) connected to the central area (12) only by the supports (16); Attaching a pair of deformation measuring elements (1-6) to only the top surface of each support (16) on opposite sides of, and spaced apart from, a neutral axis (18) of the support (16), wherein the deformation measuring elements (1-6) are configured to convert tensile and compressive forces on the surface of the top surface of the support (16), which are caused by deformation of the support (16), into electrical signals; and electrical connection of the deformation measuring elements (1-6) of each carrier to a processing circuit. [16] Method (100) according to claim 15, wherein the blind recesses further define bending elements (17) transverse to each support (16) which are arranged at the distal end of the support (16) from the central area (12), and wherein the bending elements (17) are connected to the annular body (14). [17] Method (100) according to one of claims 15-16, further comprising: Drilling a mounting opening through the central area (12), wherein the central area (12) is a tool adapter plate, WAP (12), which is set up for connection with a first object; Drilling and tapping a plurality of fastening holes in the upper surface of the annular body (14), wherein the annular body (14) is a mounting adapter plate, MAP (14), which is configured for connection with a second object. [18] Method (100) according to any one of claims 15-17, wherein the first object is a robot tool or a mechanical coupling with a robot tool; and the second object is a robot arm or a mechanical coupling with a robot arm. [19] Method (100) according to one of claims 15-18, further comprising drilling a strain-concentrating opening (36) through each support (16) between each pair of deformation measuring elements (1-6) on the upper surface of the support (16).

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