Single-beam 6-axis force / torque sensor

Abstract

This invention provides a 6-axis force / torque sensor having a single multi-segment variable beam. [Solution] The 6-axis force and torque (F / T) sensor 10 includes first and second adapters configured to connect to first and second objects, and further includes a single multi-segment variable beam 20 connecting the first adapter 12 to the second adapter. The variable beam has multiple segments, each segment extending in a direction perpendicular to the segment it connects to. A first pair of strain gauges 24 are mounted on only one side of the first variable beam segment 20B, and a second pair of strain gauges 26 are mounted on only one side of the second variable beam segment 20C, and are oriented perpendicular to each other on the same plane. A third pair of strain gauges 28 are mounted on only one side of the third variable beam segment 20D in a plane perpendicular to the planes of the first and second pairs of strain gauges.

Description

Technical Field

[0001] This application claims priority to U.S. Provisional Application No. 63 / 783,427 filed on April 4, 2025, and U.S. Application No. 19 / 632,705 filed on March 30, 2026. The respective disclosures of each of these referenced documents are hereby incorporated by reference in their entirety into the present specification.

[0002] The present disclosure relates generally to robotics, and in particular to a 6-axis force / torque sensor having a single multi-segment deformable beam.

Background Art

[0003] Force and / or torque (F / T) sensors are well known in the field of robotics. F / T sensors measure the forces and torques experienced by a robot arm and provide these data to the robot control system. F / T feedback and monitoring are extremely critical in many robotic operations. For example, in force-controlled operations such as material removal (drilling, grinding, polishing, etc.), an F / T sensor mounted on the robot arm detects the actual force applied by the robot tool to the workpiece, and the robot arm (or a compliance structure) is controlled to maintain the contact force below a set value. Examples of multi-axis F / T sensors and F / T resolution techniques include those described in U.S. Patent Nos. 10,422,707, 10,067,019, 11,892,364, 11,747,224, 11,491,663, 11,085,838, and published U.S. Patent Application No. 2023 / 0049155, all of which are assigned to the assignee of the present disclosure and are hereby incorporated by reference in their entirety into the present specification.

[0004] In particular, the aforementioned "'707 Patent" discloses a compact F / T sensor arranged as a hub and annular ring connected by variable beams, similar to the spokes of a wheel. The F / T sensor of the '707 Patent may be machined from a single piece of metal, thereby reducing the number of parts and facilitating manufacturing. The strain gauges are mounted on only one side (upper side) of each variable beam, opposite the neutral axis (on both sides of the neutral axis), which further promotes a compact design and reduces manufacturing costs by facilitating the installation of strain gauges. Strain-enhancing holes may be formed between each pair of strain gauges. While the F / T sensor of the '707 Patent provides an excellent F / T measurement solution for many use cases, the fact that not all strain gauges are on the same plane is advantageous for decomposing force and torque from the measurement of strain gauge signals.

[0005] The background art section of this specification is provided to place aspects of this disclosure in a technical and operational context in order to help those skilled in the art understand its scope and usefulness. Approaches described in the background art section may be pursued, but are not necessarily previously conceived or pursued. Unless expressly designated as such, no description in this specification shall be considered prior art simply because it is included in the background art section. [Overview of the project]

[0006] The following is a simplified summary of the disclosure to provide a basic understanding to those skilled in the art. This summary is not intended to be a broad overview of the disclosure, nor to identify the main / essential elements of the aspects of the disclosure, nor to define the scope of the disclosure. The sole purpose of this summary is to present some of the concepts disclosed herein in a simplified form as a prelude to the more detailed explanations that follow.

[0007] According to one or more embodiments described and claimed herein, a 6-axis F / T sensor comprises first and second mounting adapters configured to be rigidly attached to first and second objects, respectively. A single multi-segment variable beam having multiple segments connects the first and second mounting adapters. Each segment of the multi-segment variable beam extends parallel to the axes of the Cartesian coordinate system of the F / T sensor. Thus, each beam segment extends in a direction orthogonal to the direction of the segment(s) to which it is connected. In one embodiment, the first and second mounting adapters are arranged adjacent to each other, for example, spaced apart in the y-direction, and the multi-segment variable beam extends around the pair of mounting adapters, with each segment parallel to the x-axis or y-axis of the F / T sensor coordinate system. Thus, each beam segment is connected perpendicularly to one or two adjacent beam segments. The multi-segment variable beam comprises connecting beam segments connected to first and second mounting adapters, and three variable beam segments connected between the first and second connecting beam segments. Strain gauges are mounted on only one side of a selected set of variable beam segments, on both sides of the neutral axis. The surfaces of the variable beam segments to which the strain gauges are mounted are easily accessible (i.e., the strain gauges are not mounted on the "inner" surfaces of the variable beam segments between the multi-segment variable beam and the first and second mounting adapters). Below the strain gauges, strain-enhancing through-passages are optionally formed in the selected variable beam segments. Each surface of the variable beam segment to which the strain gauges are mounted defines a plane. The first and second pairs of strain gauges are mounted on the surfaces of their respective variable beam segments in the same plane, but oriented in orthogonal directions. The third pair of strain gauges is mounted on the surface of a variable beam segment in a plane perpendicular to the planes of the first and second strain gauge pairs.

[0008] One embodiment relates to a six-axis force and torque (F / T) sensor. The F / T sensor includes a first adapter configured to connect to a first object and a second adapter configured to connect to a second object. The F / T sensor further includes a single multi-segment variable beam connecting the first adapter to the second adapter. The variable beam comprises multiple segments. Each segment extends in a direction orthogonal to the segment(s) it connects to. A first pair of strain gauges is mounted on only one side of the first variable beam segment. A second pair of strain gauges is mounted on only one side of the second variable beam segment. The first and second pairs of strain gauges are coplanar but oriented in orthogonal directions. A third pair of strain gauges is mounted on only one side of the third variable beam segment. The third pair of strain gauges lies in a plane orthogonal to the planes of the first and second pairs of strain gauges. [Brief explanation of the drawing]

[0009] The Disclosure will be described in more detail below with reference to the accompanying drawings illustrating aspects thereof. However, the Disclosure should not be construed as being limited to the aspects described herein. Rather, these aspects are provided to make the Disclosure thorough and complete and to fully convey the scope of the Disclosure to those skilled in the art. Throughout the drawings, similar numbers refer to similar elements.

[0010] [Figure 1] Figure 1 is a top perspective view of a 6-axis F / T sensor having a single variable beam, with one pair of strain gauges on the same surface of each selected variable beam segment.

[0011] [Figure 2] Figure 2 is a perspective view of the bottom surface of the F / T sensor shown in Figure 1.

[0012] [Figure 3] Figure 3 is a schematic diagram of the quarter bridge wiring of a pair of strain gauges.

[0013] [Figure 4] Figure 4 is a perspective view of the top surface of a 6-axis F / T sensor with a single variable beam, and features two pairs of strain gauges on the same surface of each selected variable beam segment.

[0014] [Figure 5] Figure 5 is a schematic diagram of the quarter bridge wiring of a pair of strain gauges.

[0015] [Figure 6] Figure 6 is a schematic diagram of the quarter bridge wiring of a pair of strain gauges.

[0016] [Figure 7] Figure 7 is a block diagram of the controller electronics for the F / T sensor shown in Figure 1. [Modes for carrying out the invention]

[0017] For the sake of brevity and clarity, this disclosure is described primarily by reference to its exemplary embodiments. Numerous specific details are given in the following description to provide a thorough understanding of this disclosure. However, it will be readily apparent to those skilled in the art that this disclosure can be implemented without being limited to these specific details. In this description, well-known methods and structures are not described in detail in order to avoid unnecessarily obscuring the disclosure.

[0018] Figure 1 is a top perspective view of a single-beam 6-axis F / T sensor 10 according to one aspect of the present disclosure. Figure 2 is a bottom perspective view of the same F / T sensor 10. The F / T sensor 10 includes first and second mounting adapters 12, 16, a single multi-segment variable beam 20 connecting the first adapter 12 to the second adapter 16, and three pairs of strain gauges 24, 26, 28 attached to only one side of the first, second, and third variable beam segments 20B, 20C, and 20D, respectively. Figures 1 and 2 show a Cartesian coordinate system for the purposes of discussion herein only.

[0019] The first mounting adapter 12 is configured to be rigidly attached to a first object, such as a robot arm. Mounting through-holes 14 are provided on the first mounting adapter 12 in a regular pattern to facilitate connection of the first mounting adapter 12 to various robot arms or adapters. In other embodiments, the mounting holes 14 may be threaded and / or provided in a different pattern. The second mounting adapter 16 is configured to be rigidly attached to a second object, such as a robot tool or end effector. Mounting through-holes 18 are provided on the second mounting adapter 16 in a regular pattern to facilitate connection of the second mounting adapter 16 to various robot tools or end effectors. In other embodiments, the mounting holes 18 may be threaded and / or provided in a different pattern. The first and second mounting adapters 12, 16 (and connecting beam segments 20A, 20E) are separated by an oblique gap 22 and therefore do not come into direct contact with each other.

[0020] A single multi-segment variable beam 20 connects a first mounting adapter 12 to a second mounting adapter 16. The multi-segment variable beam 20 comprises multiple beam segments, each beam segment extending in a direction orthogonal to the beam segment(s) it connects to. Specifically, the multi-segment variable beam 20 comprises first and second connecting beam segments 20A and 20E, respectively, which connect to the first and second mounting adapters 12 and 16. Similar to the first and second mounting adapters 12 and 16, the first and second connecting beam segments 20A and 20E are separated by an oblique gap 22 and therefore do not come into contact with each other. Multiple variable beam segments 20B, 20C, and 20D connect a first connecting beam segment 20A to a second connecting beam segment 20E. None of the variable beam segments 20B, 20C, and 20D come into contact with either the first or second mounting adapters 12 or 16. Rather, the variable beam segments 20B, 20C, and 20D extend around the first and second mounting adapters 12 and 16, separated from them by small gaps. All beam segments 20A-E connect perpendicularly to adjacent beam segments(s).

[0021] More specifically, the first connecting beam segment 20A extends from the first mounting adapter 12 in the -y direction. The first variable beam segment 20B extends from the first connecting beam segment 20A in the -x direction. The second variable beam segment 20C connects perpendicularly to the first variable beam segment 20B and extends in the +y direction. The third variable beam segment 20D connects perpendicularly to the second variable beam segment 20C and extends in the +x direction. Finally, the second connecting beam segment 20E connects perpendicularly to the third variable beam segment 20D, extends in the -y direction, and connects to the second mounting adapter 16.

[0022] In one aspect, the strain gauges 24, 26, 28 are attached in pairs to only one respective side of each of the three deformable beam segments 20B to D. Each pair of strain gauges is mounted on the surface of the deformable beam segment, on the opposite side of the neutral axis of the beam segment surface (on both sides across the neutral axis), at a distance from the neutral axis. The neutral axis is a line running substantially through the center of the surface of the beam segment, and is the line at which the compressive strain experienced on the left side of the beam segment transitions to the tensile strain on the right side. Accordingly, the beam segment experiences no strain at the neutral axis. Each strain gauge is rigidly attached to the surface of the beam segment by an adhesive or the like, whereby tensile force and compressive force at the surface of the beam segment are transmitted to the strain gauge, and the strain gauge undergoes a change in electrical resistivity proportional to the strain. The strain gauges are arranged in a direction along the length of the respective beam segment, that is, parallel to the neutral axis on the surface of the beam segment.

[0023] Specifically, the first pair of strain gauges 24 is attached to the upper surface of the first deformable beam segment 20B. The second pair of strain gauges 26 is attached to the upper surface of the second deformable beam segment 20C. The third pair of strain gauges 28 is attached to the outer surface of the third deformable beam segment 20D.

[0024] The first and second pairs of strain gauges 24, 26 lie in the same plane (x-y plane) but face in mutually orthogonal directions, that is, the first pair of strain gauges 24 is oriented parallel to the x-axis, and the second pair of strain gauges 26 is oriented parallel to the y-axis. The third pair of strain gauges 28 is also mounted oriented parallel to the x-axis. However, the third pair of strain gauges 28 lies in a plane (x-z plane) orthogonal to the plane of the first and second pairs of strain gauges 24, 26.

[0025] In the embodiment shown in Figure 1, each pair of strain gauges 24, 26, and 28 on each variable beam segment 20B to D are wired in a quarter bridge topology using two fixed resistors, as shown in Figure 3.

[0026] As shown in Figure 1, one or more additional strain gauges 36 may be attached to a non-stress member, such as the side of the first mounting adapter 12. Since these strain gauges 36 are not subject to mechanical strain, their output changes only with temperature and can provide information for temperature compensation of the strain gauge pair 24, 26, 28. Temperature compensation is described, for example, in some of the incorporated patents mentioned above.

[0027] Figure 4 shows another embodiment of the single-beam 6-axis F / T sensor 10, in which two pairs of strain gauges are mounted on each beam surface to be instrumented. Specifically, a fourth pair of strain gauges 30 is mounted on the upper surface of the first variable beam segment 20B, substantially aligned with the first pair of strain gauges 24. A fifth pair of strain gauges 32 is mounted on the upper surface of the second variable beam segment 20C, substantially aligned with the second pair of strain gauges 26. A sixth pair of strain gauges 34 is mounted on the outer surface of the third variable beam segment 20D, substantially aligned with the third pair of strain gauges 28. In this embodiment, the four strain gauges on each variable beam segment are wired in a half-bridge topology using span resistors R1 and R2, as shown in Figure 5.

[0028] In another embodiment (not shown), the fourth, fifth, and sixth pairs of strain gauges 30, 32, and 34 are mounted on the sides of the first, second, and third variable beam segments 20B to D, opposite to the first, second, and third pairs of strain gauges 24, 26, and 28. In this embodiment, the four strain gauges on each variable beam segment are wired in a full-bridge topology as shown in Figure 6.

[0029] In one embodiment, as best seen in Figure 2, each variable beam segment 20B-D includes through passages 38, 40, and 42, respectively. While these may be substantially any shape functionally, Figures 1, 2, and 4 show a “dogbone” shape with two round or elliptical through holes connected by a linear through cut. Strain gauge pairs 24, 26, 28, 30, 32, and 34 are preferably mounted over one of the through holes (as shown in Figure 1 for strain gauge 28 and through passage 42). This reduces the thickness of each variable beam segment 20B-D and enhances the strain generated on the adjacent surface to which the strain gauge pairs 24, 26, 28, 30, 32, and 34 are mounted. The double through-hole design of the through-passage facilitates the embodiment shown in Figure 4, in which two pairs of strain gauges are mounted on each instrumentation surface of the variable beam segments 20B-D (and potentially on the opposite side of the beam segments, resulting in up to four pairs of strain gauges per beam segment, which may be wired in a full-bridge topology). The connecting through-cuts ensure that the strain gauges receive the same amount of strain when mounted over both through-holes, because if the region between the holes is solid, the strain can move (transmit) between the pairs of gauges from left to right across the beam segment.

[0030] Figure 7 shows the F / T sensor 10 along with a block diagram of the controller 44, which includes a measurement and processing circuit 46, a memory 48, and optionally (as indicated by dashed lines) an input / output (I / O) circuit 50. The measurement and processing circuit 46 is configured to receive electrical signals from each strain gauge of each pair of strain gauges 24, 26, 28, 30, 32, 34 (only strain gauge pairs 24, 26, and 28 are shown for brevity) and decompose these signals into forces and / or torques applied between the first and second mounting adapters 12, 16. In one embodiment, the forces are aligned along the F / T sensor coordinate axes, as shown in Figure 1, and the torques are moments around those axes, generating a 6-axis F / T output. Algorithms for decomposing the strain gauge output into forces and torques are known in the art and are disclosed, for example, in the incorporated patent mentioned above. These algorithms may be embodied in machine-readable code stored in memory 48, which is accessed by the measurement and processing circuit 46. Although not shown in Figure 6, one or more non-stress temperature-compensated strain gauges 36 may be connected to the controller 44, and the measurement and processing circuit 46 may further perform temperature compensation on the force and torque values ​​derived from strain gauge pairs 24, 26, 28, 30, 32, and 34.

[0031] An optional I / O circuit 50 may preprocess the strain gauge output signal before processing by the measurement and processing circuit 46 by performing amplification, low-pass filtering to reduce noise, and analog-to-digital conversion. The I / O circuit 50 may also postprocess the resolved force and torque, for example by comparing them to a predetermined threshold to trigger an alarm if excessive force or torque is detected, or by converting the force and torque to a format required by, for example, a tactile feedback circuit in a robot controller or other application. Alternatively, the measurement and processing circuit 46 may perform all formatting of the output data.

[0032] The measurement and processing circuit 46 may include any sequential state machine (sequential state machine) capable of operating to execute machine instructions stored in the memory 48 as machine-readable computer programs, for example, one or more hardware-implemented state machines (e.g., discrete logic, FPGA, ASIC, etc.), one or more stored programmable general-purpose processors such as a microprocessor or digital signal processor (DSP) with appropriate firmware, or any combination of the above.

[0033] The memory 48 may comprise any non-transient machine-readable medium known or developed in the art, including, but not limited to, magnetic media (e.g., floppy disks, hard disk drives), optical media (e.g., CD-ROMs, DVD-ROMs), solid-state media (e.g., SRAM, DRAM, DDRAM, ROM, PROM, EPROM, flash memory, solid-state disks), or similar. Those skilled in the art will understand that in some embodiments, the memory 48 may be integrated into the measurement and processing circuit 46.

[0034] An optional I / O circuit 50 may include a receiver circuit configured to receive, amplify, and digitize electrical signals from strain gauge pairs 24, 26, 28, 30, 32, and 34. The I / O circuit 50 may further include a transmitter or interface circuit configured to output force / torque data useful to other systems or components, such as an excessive force indicator (e.g., flashing light, audible alarm, etc.) or data for a tactile feedback system.

[0035] Embodiments of this disclosure offer significant advantages over the prior art and may achieve one or more of the following technical effects: The F / T sensor is compact, enabling deployment in numerous robotic operations requiring small, agile robots, such as warehouse automation. Manufacturing costs are reduced and yields are improved by mounting strain gauges only on the top or outer surface of the variable beam segment. By oriented two pairs of strain gauges in different directions and a third pair in a plane orthogonal to the planes of the other two pairs, the signals from the strain gauges are easily resolved by the six-axis forces and torques acting on the F / T sensor. Mounting one or more strain gauges in non-stress positions facilitates temperature compensation and improves accuracy over a wide range of operating conditions.

[0036] While this specification describes strain gauges as stress transducers, those skilled in the art will understand that other technologies may be advantageously applied to the F / T sensor of the present invention. For example, capacitive gauges, fiber Bragg gratings, surface acoustic wave (SAW) or piezoelectric sensors, or any combination thereof, may be applied as stress transducers.

[0037] In general, all terms used herein should be interpreted according to their common meaning in the art to which they relate, unless explicitly given a different meaning or implied by the context in which they are used. All references to an element, apparatus, component, means, step, etc., should be interpreted non-restrictively as referring to at least one instance of that element, apparatus, component, means, step, etc., unless expressly stated otherwise. Any feature of any embodiment disclosed herein may, whenever appropriate, be applied to any other embodiment. Similarly, any advantage of any embodiment may be applied to any other embodiment, and vice versa. Other purposes, features, and advantages of the embodiments contained herein will become apparent from the description. Where used herein, the term “configured to” means set up, organized, adapted, or arranged to operate in a particular manner, and is synonymous with “designed to,” or, in the case of processing circuits and / or software, “programmed to.”

[0038] This disclosure may, of course, be implemented in ways other than those specifically described herein, without departing from the essential features of this disclosure. This embodiment should be considered in all respects to be illustrative and non-limiting, and all modifications that fall within the meaning and equivalents of the appended claims are intended to be incorporated therein.

Claims

1. A single-beam type six-axis force and torque (F / T) sensor (10), A first mounting adapter (12) configured to be rigidly attached to a first object, A second mounting adapter (16) configured to be rigidly attached to a second object, A single multi-segment variable beam (20) connecting the first mounting adapter (12) to the second mounting adapter (16), wherein the multi-segment variable beam (20) comprises a plurality of beam segments (20B, 20C, 20D), each beam segment extending in a direction perpendicular to the beam segment (20B, 20C, 20D) to which it is connected, and a single multi-segment variable beam (20), A first pair of strain gauges (24) attached to only one side of a first variable beam segment (20B), and a second pair of strain gauges (26) attached to only one side of a second variable beam segment (20C), wherein the first and second pairs of strain gauges (24, 26) are on the same plane but oriented in orthogonal directions, A third pair of strain gauges (28) attached to only one side of the third variable beam segment (20D), wherein the third pair of strain gauges (28) lies on a plane perpendicular to the plane of the first and second pairs of strain gauges (24, 26), An F / T sensor (10) is provided.

2. The F / T sensor (10) according to claim 1, wherein the strain gauges in each pair of strain gauges (24, 26, 28) are positioned on both sides of the neutral axis of each of the variable beam segments (20B, 20C, 20D), spaced apart from the neutral axis, and are configured to convert the tensile and compressive forces on one side surface of each of the variable beam segments (20B, 20C, 20D) caused by the deformation of each of the variable beam segments (20B, 20C, 20D) into electrical signals.

3. The F / T sensor (10) according to claim 1, further comprising a measuring circuit (46) configured to measure the direction and magnitude of three forces and three torques between the first and second objects in response to electrical signals from all strain gauges (24, 26, 28), wherein the forces and torques are relative to the coordinate system of the F / T sensor (10).

4. The F / T sensor according to claim 3, further comprising at least one temperature-compensated strain gauge (36) mounted on the surface of the F / T sensor (10) which is not subject to mechanical stress in response to a force or torque applied to the F / T sensor (10), and the measuring circuit (46) is further configured to perform temperature compensation on the measured force and torque in response to signals from the temperature-compensated strain gauge (36).

5. The F / T sensor (10) according to claim 1, wherein at least one variable beam segment (20B, 20C, 20D) is provided with strain concentration through passages (38, 40, 42) formed through the variable beam segment (20B, 20C, 20D) below the strain gauges (24, 26, 28).

6. The multi-segment variable beam (20) further comprises a first connecting beam segment (20A) connected to the first mounting adapter (12) and the first variable beam segment (20B), and a second connecting beam segment (20E) connected to the third variable beam segment (20D) and the second mounting adapter (16), according to claim 1, the F / T sensor (10).

7. The F / T sensor (10) according to claim 1, wherein the first and second mounting adapters (12, 16) and the multi-segment variable beam (20B) are all machined from a single metal material to form an integrated unit.

8. The F / T sensor (10) according to claim 1, wherein each pair of strain gauges (24, 26, 28) attached to a variable beam segment are electrically connected in a quarter bridge topology using two fixed resistors (R1, R2).

9. A fourth pair of strain gauges (30) mounted on the same side as the first pair of strain gauges (24) of the first variable beam segment (20B), and a fifth pair of strain gauges (32) mounted on the same side as the second pair of strain gauges (26) of the second variable beam segment (20C), wherein the fourth and fifth pairs of strain gauges (30, 32) are on the same plane but oriented in orthogonal directions, A sixth pair of strain gauges (34) mounted on the same side of the third pair of strain gauges (28) of the third variable beam segment (20D), wherein the sixth pair of strain gauges (34) lies on a plane perpendicular to the plane of the fourth and fifth pairs of strain gauges (30, 32), The F / T sensor (10) according to claim 1, further comprising:

10. The F / T sensor (10) according to claim 9, wherein the two pairs of strain gauges attached to each variable beam segment are electrically connected in a half-bridge topology using span resistors (R1, R2).

11. A fourth pair of strain gauges (30) mounted on the side of the first variable beam segment (20B) opposite to the first pair of strain gauges (24), and a fifth pair of strain gauges (32) mounted on the side of the second variable beam segment (20C) opposite to the second pair of strain gauges (26), wherein the fourth and fifth pairs of strain gauges (30, 32) are on the same plane but oriented in orthogonal directions, A sixth pair of strain gauges (34) is mounted on the third variable beam segment (20D) opposite to the third pair of strain gauges (28), wherein the sixth pair of strain gauges (34) lies on a plane perpendicular to the plane of the fourth and fifth pairs of strain gauges (30, 32), The F / T sensor (10) according to claim 1, further comprising:

12. The F / T sensor (10) according to claim 9, wherein the two pairs of strain gauges attached to each variable beam segment are electrically connected in a full-bridge topology.

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