Screw-type actuator with integrated detection capabilities

Abstract

The linear actuator comprises a first element that is stationary in the axial direction but rotatably driven. A second element is rotatably stationary but is driven by the first element to move in the axial direction. At least one sensor device is attached to the second element and is operable to transmit detected information away from the linear actuator.

Description

Technical Field

[0001] This application is based on and claims priority to U.S. Provisional Patent Application No. 63 / 529,529, filed on July 28, 2023, entitled "SCREW-TYPE ACTUATOR WITH INTEGRATED SENSING CAPABILITY". The above application is hereby incorporated by reference in its entirety for all purposes.

[0002] The present invention relates generally to mechanical linear actuators. More particularly, the present invention relates to screw-type actuators.

Background Art

[0003] Typical electromechanical brake systems require an actuator capable of providing linear force and brake clamp force feedback to a related vehicle control system. An exemplary linear actuator is a ball screw assembly that includes a ball train interposed between a ball track formed on the outer surface of a ball screw shaft and a ball track formed on the inner surface of a ball screw nut. The prior art can achieve linear force sensing by positioning a dedicated load cell between the actuator and the housing. However, the load cell increases the overall length of the assembly, thus occupying valuable system space and increasing system complexity. Additionally, dimensional alignment of the load cell with its mating components is important for accurate and reproducible force sensing and for maintaining requirements of minimum preload.

[0004] The present invention recognizes and addresses the considerations of prior art constructs and methods.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] In one aspect, the disclosure provides a linear actuator comprising a first element that is stationary in the axial direction but rotatably driven. A second element is rotatably stationary but is driven by the first element to move in the axial direction. At least one sensor device is attached to the second element and the sensor device is operable to transmit detected information away from the linear actuator.

[0007] In some exemplary embodiments, at least one sensor device may be positioned in a recess defined in a second element. For example, the recess may extend perpendicular to the longitudinal axis of the linear actuator. The recess may be arc-shaped. Furthermore, the recess may define a first through-hole and a second through-hole near each end of the recess, with the sensor mounting surface defined between the first and second through-holes. In such embodiments, the through-hole may extend tangentially to the longitudinal axis of the linear actuator or radially to the longitudinal axis of the linear actuator.

[0008] In some exemplary embodiments, the first element may be a screw shaft, and the second element may be a nut positioned along the screw shaft. In such embodiments, at least one sensor device may be mounted in a recess defined on the outer surface of the nut. Alternatively, or additionally, at least one sensor device may be mounted in a recess defined on the inner surface of the nut. The recess may define one or more of a plane, concave, or convex surface on which at least one sensor device is mounted.

[0009] In some exemplary embodiments, the first element may be a nut, and the second element may be a screw shaft.

[0010] The linear actuator may preferably include a screw-type actuator such as a ball screw assembly.

[0011] In some exemplary embodiments, at least one sensor device may comprise multiple sensors that measure at least two different parameters. For example, at least one sensor device may comprise at least one of a strain sensor, a temperature sensor, an accelerometer, a vibration sensor, and an orientation sensor. The linear actuator may comprise processing circuitry mounted onboard to the second element.

[0012] The accompanying drawings incorporated herein and constituting part thereof illustrate one or more embodiments of the present invention and are useful in illustrating the principles of the present invention together with this specification.

[0013] A complete and possible disclosure of the present invention, including its best mode directed to those skilled in the art, is described herein with reference to the accompanying drawings. [Brief explanation of the drawing]

[0014] [Figure 1A] This is a diagram of a linear actuator with integrated detection capability according to an embodiment of the present invention. [Figure 1B] This is a diagram of a linear actuator with integrated detection capability according to an embodiment of the present invention. [Figure 2] Various onboard sensors that can be used with the linear actuators shown in Figures 1A and 1B are diagrammatically illustrated. [Figure 3] This is a schematic diagram of a brake assembly including an embodiment of a linear actuator according to an embodiment of the present invention. [Figure 4] This is an enlarged schematic cross-sectional view of a linear actuator that may be used with the brake assembly shown in Figure 3. [Figure 5] Various mounting surfaces for one or more integrated sensors in a linear actuator according to embodiments of the present invention are shown. [Figure 6]Various mounting surfaces for one or more integrated sensors in a linear actuator according to embodiments of the present invention are shown. [Figure 7] Various mounting surfaces for one or more integrated sensors in a linear actuator according to embodiments of the present invention are shown. [Modes for carrying out the invention]

[0015] The use of repeated reference letters in this specification and drawings is intended to represent identical or similar features or elements of the present invention in accordance with this disclosure.

[0016] Preferred embodiments of the present invention are described in detail, and one or more of these embodiments are shown in the accompanying drawings. Each embodiment is provided for illustrative purposes only, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations of the invention can be made without departing from the scope and spirit of the invention. For example, a feature shown or described as part of one embodiment may be used in another embodiment, resulting in yet another embodiment. It is therefore intended that such modifications and variations will be covered, so that the invention falls within the scope of the appended claims and their equivalents.

[0017] As used herein, terms referring to the orientation or position of a linear actuator, such as but not limited to “vertical,” “horizontal,” “top,” “bottom,” “above,” or “below,” refer to the orientation and relative position in the intended operation, whether in a braking system or otherwise. Furthermore, as used herein and in the appended claims, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless otherwise specified or evident from the context, the phrase “X uses A or B” is intended to mean any of the natural inclusive substitutions. That is, the phrase “X uses A or B” is satisfied by any of the following examples: X uses A, X uses B, or X uses both A and B. Furthermore, the articles “a” and “an” used in this application and the attached claims should be understood as meaning “one or more” unless otherwise specified or unless the context makes it clear that they are directed toward the singular form. Throughout this specification and the claims, unless the context indicates otherwise, the following terms have at least the meanings explicitly associated herein. The meanings identified below are not necessarily limiting to the terms, but merely provide illustrative examples of the terms. The meanings of “a,” “and,” and “the” may include references to the plural form, and the meaning of “in” may include “in” and “on.” The phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment, although it may.

[0018] Referring to the drawings, FIGS. 1A and 1B show alternative embodiments of a linear actuator according to the present invention. In this regard, FIG. 1A shows a linear actuator 10a having an axially movable portion that moves linearly with respect to an axially stationary portion. In this case, the linear actuator 10a includes a screw-type actuator, and the axially stationary portion in the screw-type actuator is configured as a rotatable shaft 12a. The axially movable portion is configured as a nut 14a that moves axially along the shaft when rotated. The direction of rotation of the shaft 12a determines in which direction the nut 14a advances. Various screw-type actuators that can utilize the teachings of the present invention include ball screws (recirculating and non-recirculating), lead screws (including planetary lead screws), and roller screws.

[0019] One or more sensor devices 16a are suitably mounted on the nut 14a of the linear actuator 10a. In this case, the sensor device 16a is provided in a receptacle disposed on the outer surface of the nut 14a. Data from the sensor device 16a can be provided to an external device using a suitable lead wire 18a or a suitable wireless transmission technology (such as Zigbee, Bluetooth, etc.). Alternatively, the sensor can be disposed in a groove or other receptacle defined on the inner circumference of the nut 14a as shown at 16a'.

[0020] Figure 1B shows an alternative embodiment of the screw-type linear actuator 10b, in which the shaft 12b in the screw-type linear actuator 10b moves axially with respect to the axially stationary nut 14b. In this case, the nut 14b is rotated to move the shaft 12b axially with respect to the nut. The direction of rotation of the nut 14b determines in which direction the shaft 12b advances. One or more sensor devices 16b are suitably mounted on the shaft 12b of the linear actuator 10. In this case, the sensor device 16b is provided in a receptacle arranged on the outer surface of the shaft 12b a. The data from the sensor device 16b can be provided to a device external to the linear actuator using a suitable lead wire 18b or a suitable wireless transmission technology (such as Zigbee, Bluetooth, etc.).

[0021] In the above embodiments, the sensor devices 16a - b are mounted on the axially movable part of the linear actuator. However, depending on the type of sensor, it may be more desirable to arrange the sensor on the axially stationary part of the linear actuator. In some embodiments, one or more sensors can be arranged on the axially movable part of the linear actuator, and one or more other sensors are arranged on the axially stationary part of the linear actuator. Further, as will be described below, the surface on which the sensor devices 16a - b are mounted can preferably be configured to enhance the detection of the parameter of interest.

[0022] Figure 2 shows an example of a sensor device 116 that may be used in various embodiments of the present invention. In this case, the sensor device 116 is mounted on a suitable surface (or a suitable surface for each) 120 of the axially movable portion and / or the axially stationary portion of the linear actuator. Suitable sensor and signal types may include, but are not limited to, digital, analog, discrete, resistive, capacitive, inductive, piezoelectric, electromagnetic, and / or optical / laser types. In this case, the sensor device 116 includes one or more of a force sensor (strain gauge) 116a, a temperature sensor 116b, an accelerometer / vibration sensor 116c, and an orientation sensor 116d. As those skilled in the art will understand, the force sensor 116a typically measures the force transmitted to the linear actuator from an external element such as a brake assembly with which the linear actuator is engaged. The temperature sensor 116b may be used to measure the temperature of the linear actuator and / or the ambient temperature as needed or desired. The accelerometer / vibration sensor 116c can be used to measure vibrations imposed on the linear actuator, for example, so that appropriate maintenance can be performed. In many cases, it may be desirable to use multiple orientation sensors 116d so that the orientation can be determined with respect to multiple axes.

[0023] As described above, data from the sensors is provided to external devices via wired or wireless transmission as shown in 122. In some cases, it may be desirable to provide data from various sensors in its "raw" (i.e., unprocessed) form. In other cases, it may be desirable to perform initial processing of at least some of the data using a circuit 124 located onboard the linear actuator. For example, analog data from sensor device 116 can be digitized in circuit 124 for transmission to external devices. Furthermore, information from multiple sensor devices 116 can be appropriately multiplexed for transmission to external devices. Circuit 124 may be, for example, a PCBA directly mounted on the actuator and / or an installed ribbon connector / cable that processes signals and connects them to the entire system. External devices can receive sensor data continuously, as needed, or when queried by the external device. For example, circuit 124 may be configured to transmit sensor data to external devices only when certain conditions are met, such as exceeding a threshold, as needed or desired.

[0024] Figure 3 shows an exemplary application in which the principle of the present invention may be used. In this regard, the brake assembly 200 includes a linear actuator in the form of a ball screw assembly 202. The brake assembly 200 selectively applies frictional braking force to a disc 204 that rotates integrally with a wheel, such as that of an automobile. The brake assembly 200 includes a caliper 206 having a first backup plate 208 that supports a first pad 210. A second backup plate 212 supports a second pad 214. As shown, the disc 204 is sandwiched between the first pad 210 and the second pad 214.

[0025] The caliper 206 includes a first body 216 fixed to a second body 218. The cover 220 is fixed to the second body 218. As shown, the first body 216 includes a body portion 222 and an arm portion 224. The arm portion 224 is coupled orthogonally to the body portion 222 with the second backup plate 212 fixed to the inner surface of the arm portion 224.

[0026] The second body 218 includes a brake cylinder portion 226 having an open first end 228 and a second end 230 opposite in the axial direction. An extension plate 232 extends laterally downward from the second end 230. The end 228 of the brake cylinder portion 226 is fixed to the body portion 222 of the first body 216 as shown. A piston 234 is positioned in the brake cylinder portion 226 for axial reciprocating movement. As those skilled in the art will understand, axial movement of the piston 234 to the left in this viewpoint causes the pads 210 and 214 to press against the disc 204. Movement of the piston 234 to the right releases the pressing against the disc 204. A sealing member 236 may be interposed between the cylindrical outer surface of the piston 234 and the inner surface of the brake cylinder portion 226. For example, the sealing member 236 may be an O-ring located in a groove formed in the inner surface of the brake cylinder portion 226. Furthermore, the key 238 may be disposed in radially aligned keyways on the outer surface of the piston 234 and the inner surface of the brake cylinder portion 226. The keying using the key 238 allows for the axial movement of the piston 234 and prevents rotation of the piston 234 relative to the brake cylinder portion 226.

[0027] As described above, the brake assembly 200 includes a linear actuator 202 to move the piston 234 axially. In this case, the linear actuator is in the form of a screw actuator, i.e., a non-recirculating ball screw actuator. In this regard, the caliper 206 includes an electric motor 240, a reducer 242, and a ball screw 246. As understood, the reducer 242 reduces the rotational speed of the electric motor 240. The ball screw 246 converts the rotational motion transmitted from the electric motor 240 via the reducer device 242 into linear motion in the axial direction of the piston 234.

[0028] The electric motor 240 includes an output shaft 248 that drives the reduction gear 242. In particular, a drive gear 250 is mounted on the end of the output shaft 248. The rotation of the drive gear 250 rotates the idler gear 252, which in turn rotates the driven gear 256. The driven gear 256 is mounted on the end of the ball screw shaft 258 of the ball screw 246. The cover 10 covers the gears of the reduction gear 242.

[0029] As shown, the shaft 258 passes through an opening at the end 230 of the brake cylinder portion 226, where it is supported for rotation by the bearing 260. The shaft 258 is also held against axial movement via a combination of the reduced diameter portion on one axial side of the bearing 260 and the spring clip 262 on the other axial side of the bearing 260. The shaft 258 is rotatably driven by the gear 256.

[0030] The ball screw 246 further comprises a ball screw nut 264 extending around the shaft 258. The ball screw nut 264 is held non-rotatably and axially within the piston 234, so that axial movement of the nut 264 causes accompanying axial movement of the piston 234. (Although the piston 234 and nut 264 are shown here as separate parts, embodiments in which the nut 264 and piston 234 are formed as a single part are contemplated.) The axial movement of the nut 264 is caused when the shaft 258 rotates due to a series of balls that form a row of balls arranged in opposing ball tracks defined on the opposing surfaces of the shaft 258 and the nut 264, respectively. A sensor 266, which is a force sensor here, is located in a recess defined between the piston 234 and the nut 264.

[0031] A slightly modified version of the linear actuator, similar to that shown in Figure 3, is shown in Figure 4. In this case, the linear actuator is configured as a ball screw 300 including an axially stationary shaft 302 enclosed by a ball screw nut 304. The shaft 302 rotates relative to a piston 306 which is moved axially together with the nut 304. In this regard, the nut 304 is received in a cavity defined inside the piston 306, so that both the nut 304 and the piston 306 are axially movable but not rotatable. A thrust ring 308 is interposed between the enlarged shoulder of the shaft 302 and a thrust bearing 310. Preferably, the thrust ring 308 is splined to the shaft 302 so that they rotate together. The thrust bearing 310 facilitates rotation between the thrust ring 308 and a fixed surface 312.

[0032] As shown, the multiple balls 314 form a ball row in opposing ball tracks 316 and 318 defined on the outer surface of the shaft 302 and the inner surface of the nut 304, respectively. In this case, the ball screw 300 is formed as a non-recirculating ball screw similar to that disclosed in U.S. Patent No. 11,536,355, which is incorporated herein by reference in whole for all purposes. Thus, the ball row is separated by a stopper such as a stopper 320. A link spring, including a main coil spring assembly and a return coil spring assembly, may be arranged along the ball row.

[0033] As indicated by the arrows, the axial force applied to the piston 306 is transmitted to the nut 304, then to the shaft 302 via the ball 314, and then to the thrust ring 308. A force sensor 322 is positioned on the nut 304 to measure such forces applied within the system. In this regard, since all materials undergo physical deformation (strain) under load, the ball screw nut 304 can function as a load cell. Because the nut 304 lies on the line of the applied linear force, this is a desirable location for measuring forces applied within the braking system. In this embodiment, the sensor 322 is mounted in a recess 324 defined within the outer diameter of the nut 304 and connected to other circuits for further processing and / or evaluation by a wire 326 extending through an axial groove on the nut 304. In some cases, it may be desirable to "pot" the sensor 322 (using epoxy, etc.) to further protect the sensor 322 and / or to further stabilize its mounting.

[0034] The location on which the sensor is mounted may be configured to enhance the detection of the target parameter. For example, a recess may be formed by a circumferential groove extending around the entire circumference or only a portion of the circumference of the outer or inner circumference of a nut or shaft. One or more holes may be placed within the recess to enhance the measurement sensitivity. The holes may be radial or tangential, for example, and may extend through the entire element on which they are mounted, or partially. The surface on which the sensor is mounted may be flat, concave, convex, rounded, contoured, etc., as needed or desired. In the case of a load cell, for example, the grooves and / or holes may allow for greater deformation, thereby enabling greater measurement sensitivity.

[0035] Several examples of alternative configurations for mounting various sensors are shown in Figures 5 to 7. For example, referring first to Figure 5, the nut 500 of the linear actuator has a groove 502 defined on its outer circumferential surface. In this embodiment, the groove 502 extends circumferentially around the nut, i.e., around the arcuate segment of the outer circumference of the nut. The pair of holes 504a and 504b extend tangentially through the nut 500 to locations near the respective ends of the groove 502. The surface region 506 between holes 504a and 504b provides locations for mounting one or more sensors, as shown in 508 and 510. As shown, the region 506 is “flat” in the axial direction but arcuate along the length of the groove 502. The tangential holes 504a and 504b extend below the sensor locations, providing thinner walls in this area to enhance deformation. (Note: The generally house-shaped icon overlapping the sensor 508 is a drawing artifact that does not form part of Figure 5.)

[0036] Figure 6 shows a nut 600 of a linear actuator having a groove 602 defined on its outer circumferential surface. In this embodiment, the groove 602 extends partially around the nut, i.e., around the arcuate segment of the nut's outer circumference. The pair of holes 604a and 604b extend radially through the nut 600 to locations near the respective ends of the groove 602. The surface region 606 between holes 604a and 604b provides a location for mounting one or more sensors, as shown in 608 and 610. Like region 506, region 606 is flat and arcuate. The radial holes facilitate deformation of the range to be detected by the sensors.

[0037] Figure 7 shows an alternative embodiment of the screw-type linear actuator 700. In this case, the shaft 702 forms a lead screw 704 on which a nut 706 moves axially. The nut 706 defines a groove 708 that defines a surface 710 on which a sensor device 712 (here, a strain sensing element) is mounted. For example, the sensor device 712 may be mounted using a suitable adhesive. Data from the sensor 712 is provided to other circuits via lead wires 714 positioned within the axial groove 716 defined within the nut 706. In this case, the groove 708 is formed as a tangential cut across the outer diameter of the nut 706. It can be understood that the surface on which the sensor device 712 is mounted is flat in the axial and width directions.

[0038] References are made to U.S. Patent Application Publication No. 2022 / 0364618(A1), entitled “Ball Screw Assembly with Integral Force Measurement,” which is fully incorporated herein for all purposes as described verbatim.

[0039] While one or more preferred embodiments of the present invention have been described above, it should be understood by those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit of the invention. For example, the concept is not limited to braking applications, and screw and nut type systems can be used wherever force feedback is required. It is intended that the present invention covers such modifications and variations that fall within the scope and spirit of the appended claims and their equivalents.

Claims

1. A linear actuator, A first element that is stationary in the axial direction but can be driven to rotate, A second element that is stationary and rotatable but is driven by the first element to move in the axial direction, At least one sensor device attached to the second element, wherein the sensor device is operable to transmit detected information away from the linear actuator, and Equipped with, The at least one sensor device is positioned in an arc-shaped recess defined within the second element extending perpendicularly to the longitudinal axis of the linear actuator, the recess further defines a first through-hole and a second through-hole near each end of the recess, and the sensor mounting surface is defined between the first through-hole and the second through-hole. Linear actuator.

2. The linear actuator according to claim 1, wherein the through hole extends tangentially to the longitudinal axis of the linear actuator.

3. The linear actuator according to claim 1, wherein the through hole extends radially along the longitudinal axis of the linear actuator.

4. The linear actuator according to claim 1, wherein the first element is a screw shaft and the second element is a nut positioned along the screw shaft.

5. The linear actuator according to claim 4, wherein the recess defines one of a concave or convex surface on which the at least one sensor device is mounted.

6. The linear actuator according to claim 1, wherein the at least one sensor device is mounted in a recess defined within the inner surface of the nut.

7. The linear actuator according to claim 6, wherein the recess defines one of a concave or convex surface on which the at least one sensor device is mounted.

8. The linear actuator according to claim 1, wherein the first element is a nut and the second element is a screw shaft.

9. The linear actuator according to claim 1, wherein the linear actuator comprises a screw-type actuator.

10. The linear actuator according to claim 9, wherein the screw-type actuator comprises a ball screw assembly.

11. The linear actuator according to claim 1, wherein the at least one sensor device comprises a plurality of sensors that measure at least two different parameters.

12. The linear actuator according to claim 1, wherein the at least one sensor device comprises at least one of a strain sensor, a temperature sensor, an accelerometer, a vibration sensor, and a compass sensor.

13. The linear actuator according to claim 1, wherein the at least one sensor device comprises a processing circuit mounted onboard to the second element.

Images