CN111683796A

CN111683796A - Mechanical arm and robot

Info

Publication number: CN111683796A
Application number: CN202080000958.4A
Authority: CN
Inventors: 王世全; 姜皓; 安然; 李学森
Original assignee: Feixi Technology Co ltd; Flexiv Robotics Ltd
Current assignee: Feixi Technology Co ltd; Flexiv Robotics Ltd
Priority date: 2019-09-03
Filing date: 2020-04-03
Publication date: 2020-09-18
Also published as: EP4010153A4; EP4010153A1

Abstract

A robot arm and a robot are provided. The mechanical arm (100, 10, 20, 30, 40, 50, 60) comprises a plurality of joints (121) and (127, 200a-200d, 511) and (513) a plurality of connecting arms (131) and (137, 301, 302, 411) and (413). The connecting arms are connected in sequence through joints. The at least two joints each include a sensor (205), the sensor (205) configured to measure force and torque information for more than one of six degrees of freedom (DOF) imposed on its respective joint.

Description

Mechanical arm and robot

Technical Field

The present invention relates generally to robotics, and in particular to robotic arms and robots.

Background

Robotic arms are used in many industrial fields to assist in manufacturing, assembly, and other operations. In certain applications, it is advantageous to use torque control based techniques to control the movement of the robotic arm. Such a robotic arm relies on accurate torque measurements.

Conventional robotic arms have only one single degree of freedom (DOF) torque sensor in each joint to measure the torque generated by or exerted on each corresponding joint. Such a configuration may produce errors with respect to measured torque and other forces on the joint, and thus presents a number of disadvantages to the operation of such conventional robotic arms.

Disclosure of Invention

It is therefore an object of the present invention to provide a robot arm and a robot.

The technical scheme adopted by the invention is to provide a mechanical arm. The robotic arm includes a plurality of joints and a plurality of link arms. The connecting arms are connected in sequence through joints. At least two joints each include a sensor configured to measure force and torque information in more than one of six degrees of freedom (DOF) exerted on a respective one of the at least two joints.

The invention adopts another technical scheme to provide a robot. The robot includes a plurality of joints and a connecting arm. The connecting arms are connected in sequence through joints. The joints each include a sensor configured to measure force and torque information in more than one of six degrees of freedom (DOF) exerted on the respective joint.

Drawings

In order to more clearly explain technical solutions in the embodiments of the present invention, drawings used in the description of the embodiments will be briefly described below. The drawings in the following description are merely exemplary embodiments of the invention. For a person skilled in the art, other figures can also be derived on the basis of these figures without any inventive work.

FIG. 1 illustrates a block diagram of a robotic arm according to an embodiment of the present invention.

Fig. 2-5 illustrate several exemplary arrangements of multi-degree of freedom force and/or torque sensors for joints according to some embodiments of the invention.

Fig. 6A-6C show schematic views of a robotic arm in which each joint includes a single degree of freedom torque sensor.

Fig. 7A-7C show schematic views of a robotic arm in which each joint includes multiple degree-of-freedom force and/or torque sensors.

Detailed Description

The invention will now be described in detail with reference to the accompanying drawings and examples. As will be apparent to those skilled in the art, the embodiments described in this disclosure are exemplary only and represent only a subset of all such embodiments. In particular, all other embodiments that can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention fall within the scope of the present invention.

Most conventional advanced robotic arms have a single degree of freedom torque sensor in each joint to measure the torque generated by each corresponding joint for joint torque control. Such a robot arm based on torque control has the following disadvantages.

First, it is difficult to prevent the torque sensor from being affected by forces and torques applied in other directions (e.g., different from the torque dimensions that the torque sensor is designed to sense), which is referred to as sensor cross-talk. As a result, the sensor may deviate from the true torque value under different load conditions (e.g., joint torque coupling). There are often mechanical structures designed to reduce this effect, such as the use of bearings to constrain the forces and torques that can be transmitted through the torque sensor. However, the mechanical structure may not always be able to completely reduce this effect. For example, the bearing may still deform under bending moments perpendicular to the axis of rotation. Thus, the above effects can be reduced, but not eliminated. Sensor design techniques exist to reduce the effects of torque sensor crosstalk, such as using multiple transducers (e.g., strain gauges) at different locations to compensate for the effects. However, the effectiveness of this technique is limited by design complexity, compactness requirements, and manufacturing accuracy. Second, in conventional robots, the torque sensor must be protected by a set of bearings to reduce the joint torque coupling effect. Thus, the controlled torque transmitted by the joint will be reduced by friction from the bearing, which impairs the force control accuracy. Third, the torque sensor is typically placed close to the geared drive mechanism ((e.g., harmonic drive mechanism.) the geared drive mechanism, when actuated, may apply torque and force to the sensor in other directions, which also impairs sensing accuracy.

Accordingly, the present invention provides a robotic arm having multiple degrees of freedom force and/or torque sensors in at least some joints to sense more force and/or torque information transferred through the joints and connecting arm than conventional robotic arms.

FIG. 1 illustrates a block diagram of a robotic arm 100 according to an embodiment of the present invention. The robotic arm 100 may include a plurality of connecting

arms

131 and 137 and a plurality of

joints

121 and 127. The connecting arms 131-137 are connected in sequence by the joints 121-127. The joints 121-127 may be of two basic types, pitch joints and roll joints. The roll joints (e.g.,

joints

121, 123, 125, and 127 as shown in fig. 1) may provide rotation about the longitudinal axis of the adjacent connecting arm, and the pitch joints (e.g.,

joints

122, 124, and 126 as shown in fig. 1) may provide rotation about an axis substantially perpendicular to the roll joint axis. In some examples, the end effector 140 may be connected to the last joint (e.g., joint 127). In the embodiment shown in fig. 1, the robotic arm 100 is a 7-axis robotic arm. It should be appreciated that the techniques disclosed below may also be implemented for other types of robotic arms having more or fewer axes.

At least two of the joints 121-127 may each include a sensor configured to measure force and torque information (including three-directional force and three-directional torque information) for more than one of the six degrees of freedom (DOF) of its respective joint. For example, the sensor may be a multi-degree-of-freedom force and/or torque sensor. For example,

joints

126 and 127 may be equipped with multi-degree-of-freedom force and/or torque sensors, or joint 124 and 127 may all be equipped with multi-degree-of-freedom force and/or torque sensors. Alternatively, in some embodiments, all

joints

121 and 127 may each include a multi-degree-of-freedom force and/or torque sensor.

In some embodiments, the sensors may be configured to measure the torque exerted on their respective joints in the direction of actuation of the joints. For example, if

pitch joint

122, 124, or 126 includes a multi-degree-of-freedom force and/or torque sensor, the sensor may be used to measure torque in the Y direction (perpendicular to the X and Z directions shown in fig. 1). If the

roll joint

121, 123, 125 or 127 includes a multi-degree-of-freedom force and/or torque sensor, the sensor may be used to measure the torque in the longitudinal direction between adjacent link arms. In addition, the sensor may also be configured to measure force and torque information for at least one of the other five degrees of freedom. That is, the sensor may also be configured to measure one or more of the other three directions of force and/or one or more of the other two directions of torque. For example, multiple degree-of-freedom force and/or torque sensors in the corresponding joints may be configured to measure torque in the actuation direction and force in each of the X, Y and Z directions.

For better robot dynamics and control performance, the stiffness along each sensing degree of freedom of the multi-degree-of-freedom force and/or torque sensor may be optimized. In an example, the structural stiffness of the multi-degree-of-freedom force and/or torque sensor in the actuation direction of the corresponding joint (e.g., about the joint axis) may be lower than the structural stiffness of the multi-degree-of-freedom force and/or torque sensor in other directions. In such an example, the sensing sensitivity and resolution in the degrees of freedom that can be actively adjusted by actuation may be improved. In such an example, the stiffness in the other degrees of freedom of the structure may also be kept high in order to maintain a high structural stiffness of the entire robot arm for better control performance and higher mechanical and control bandwidth.

In some embodiments, the multi-degree-of-freedom force and/or torque sensor may be a six-degree-of-freedom force and torque sensor capable of sensing torque and force information for all six degrees of freedom transmitted through the corresponding joint and the adjacent linking arm on which the joint is located. The six degree of freedom force and torque sensor is designed to sense all forces and torques experienced at the joint and adjacent link arms, and therefore can remain accurate under any combination of forces and torques. U.S. patent application No.16/456,588 discloses an exemplary 6-degree-of-freedom force and torque sensor. However, in other examples of the invention, other types of six degree-of-freedom force and torque sensors may be utilized.

Fig. 2 to 5 show different arrangements of the sensors of the joint. In fig. 2-5, joints 200a-200d each include an input 201, an output 202, a motor 203, a gear train 204, a multi-degree-of-freedom force and/or torque sensor 205, and one or more bearings 206. A stator of motor 203 may be fixed to input 201 and a rotor of motor 203 may be fixed to output 202, such that motor 203 may drive output 202 to rotate relative to input 201. A gear train 204 may be connected to the rotor of the motor 203 to regulate the rotational speed and output torque of the output 202. In some embodiments, the gear train 204 may be a harmonic drive. In some examples, a bearing 206 may be located between the input 201 and output 202 to allow relative rotation between the two parts.

In the embodiment shown in fig. 2, a multi-degree-of-freedom force and/or torque sensor 205 of joint 200a may be placed between input 201 and output 202 (e.g., between gear train 204 and output 202), similar to a joint having a single-degree-of-freedom torque sensor. In this embodiment, since the bearing 206 is designed to withstand bending moments from the output 202 to the input 201, the multi-degree-of-freedom force and/or torque sensor 205 may be configured to measure only torque in the actuation direction of the joint 200a and axial forces transmitted from the output 202 to the input 201.

In the embodiment shown in fig. 3, the multi-degree-of-freedom force and/or torque sensor 205 of the joint 200b may be placed between the input 201 and the previous link arm 301 of the joint 200 b. In this embodiment, the multiple degree of freedom force and/or torque sensor 205 may be designed to measure force and torque information for any number of degrees of freedom of six degrees of freedom. For example, multi-degree-of-freedom force and/or torque sensor 205 may be a three-degree-of-freedom force sensor capable of measuring force information in all three force directions, a three-degree-of-freedom torque sensor capable of measuring torque information in all three torque directions, a four-degree-of-freedom force and torque sensor capable of measuring force information in all three force directions and torque in the actuation direction of joint 200b, and so forth.

In an embodiment, the multi-degree-of-freedom force and/or torque sensor 205 may be a six-degree-of-freedom force and torque sensor capable of sensing all forces and torques transmitted between the previous link arm 301 and the input 201 of the joint 200 b. The joint 200b may also include a sensor circuit board 207 in communication with the multi-degree-of-freedom force and/or torque sensor 205. The sensor circuit board 207 may be located at an input end of the input portion 201 of the joint 200b and adjacent to the multi-degree of freedom force and/or torque sensor 205. The configuration of this example may greatly simplify the wiring configuration of the multi-degree-of-freedom force and/or torque sensor 205 and the sensor circuit board 207.

In the embodiment shown in fig. 4, the multi-degree-of-freedom force and/or torque sensor 205 of the joint 200c may be placed between the output 202 of the joint 200c and the latter connecting arm 302. In this embodiment, the multiple degree of freedom force and/or torque sensor 205 may be designed to measure force and torque information for any number of degrees of freedom of six degrees of freedom. For example, multi-degree-of-freedom force and/or torque sensor 205 may be a three-degree-of-freedom force sensor capable of measuring force information in all three force directions, a three-degree-of-freedom torque sensor capable of measuring torque information in all three torque directions, a four-degree-of-freedom force and torque sensor capable of measuring force information in all three force directions and torque in the actuation direction of joint 200b, and so forth.

In an embodiment, the multi-degree-of-freedom force and/or torque sensor 205 may be a six-degree-of-freedom force and torque sensor capable of sensing all forces and torques transferred between the output 202 of the joint 200b and the latter connecting arm 302. In this embodiment, the compliance between the actuation output and the sensing component (e.g., the multi-degree-of-freedom force and/or torque sensor 205) is less than in the above-described embodiments (shown in fig. 2 or 3) in which the multi-degree-of-freedom force and/or torque sensor 205 is placed inside the input or corresponding joint, and thus the torque sensing accuracy and control performance of the joint 200c may be improved.

In the embodiment shown in fig. 3 and 4, since the sensor 205 is a multi-degree-of-freedom force and/or torque sensor, it can be placed outside the input 201, output 202 and bearing 206 without compromising sensing accuracy. Thus, the multi-degree-of-freedom force and/or torque sensor 205 may be flexibly mounted anywhere on the joint to obtain design benefits, such as simplifying wiring configurations or optimizing joint design for better dynamic and control performance.

In the embodiment shown in fig. 5, joint 200d may include two multi-degree-of-freedom force and/or

torque sensors

205 and 207. The first sensor 205 may be located between the input 201 and the previous connecting arm 301 of the joint 200d, while the second sensor 207 may be located between the output 202 and the subsequent connecting arm 302 of the joint 200 d. Either of the two

sensors

205 and 207 may be redundant of the other in order to improve the accuracy of the measured force and torque information. In some examples, additional redundant sensors in the robotic arm 100 may be used for cross-checking for fault detection and better safety. In some embodiments,

sensors

205 and 207 may be substantially identical. In other embodiments, the sensor 207 may be different from the sensor 205. For example, the force and torque information measured by sensor 207 may be different than the force and torque information measured by sensor 205.

Fig. 6A-6C illustrate an example scenario in which each joint of a robotic arm includes a single degree of freedom torque sensor. In this example, the robot includes three connecting

arms

411 and 413, three

joints

511 and 513, and an end effector 414. Each of the

joints

511 and 513 comprises a sensor configured to measure only the torque in the actuation direction of the corresponding joint. When a load 610 is applied to the end effector 414, the sensors in

joints

511 and 513 may each sense a one degree of freedom torque, as shown on the robotic arm 10 in fig. 6A. When a load 620 is applied to the connecting arm 413, the sensors in

joints

511 and 512 may each sense a one degree of freedom torque, as shown on the robotic arm 20 in FIG. 6B. When a load 610 and a load 620 are simultaneously applied to the end effector 414 and the connecting arm 413, respectively, the sensors in the

joints

511 and 513 may each sense a one degree of freedom torque, as shown on the robotic arm 30 in FIG. 6C. However, in this example scenario, the robot cannot correctly identify the two

loads

610 and 620. In contrast, the robot may mistake the

loads

610 and 620 for a single force load 630 on the end effector because the sensing results of the multiple degree of freedom sensor with one load 630 applied are the same as the sensing results with two

loads

610 and 620 applied. This may therefore undermine the control performance of the robot and the ability of the robot to function properly in a complex environment.

In contrast, fig. 7A-7C illustrate an example scenario in which each joint of a robotic arm includes multiple degree-of-freedom force and/or torque sensors. In this example, the robot includes three connecting

arms

411 and 413, three

joints

511 and 513, and an end effector 414. Each of the

joints

511 and 513 comprises a sensor configured to measure force and/or torque information for a plurality of degrees of freedom, e.g. a torque in the actuation direction of the respective joint and two forces perpendicular to the actuation direction of the respective joint. When a load 610 is applied to the end effector 414 of the robotic arm 40 in fig. 7A, the sensors in

joints

511 and 513 may each sense a one degree of freedom torque and a one degree of freedom force, and the sensor in joint 512 may sense a one degree of freedom force. When a load 620 is applied to the connecting arm 413 of the robotic arm 50 in fig. 7B, the sensors in

joints

511 and 512 may each sense a one degree of freedom torque and a one degree of freedom force. When a load 610 and a load 620 are simultaneously applied to the end effector 414 and the connecting arm 413, respectively, of the robotic arm 60 in fig. 7C, the sensors in

joints

511 and 512 may each sense a one degree of freedom torque and a two degree of freedom force, and the sensor in joint 513 may sense a one degree of freedom torque and a one degree of freedom force. Therefore, in this embodiment, the two

loads

610 and 620 can be accurately identified because the sensing result of the multi-degree-of-freedom sensor in the case where one load 630 (as shown in fig. 6C) is applied is different from the sensing result in the case where the two

loads

610 and 620 are applied. Thus, with multiple degree of freedom force and/or torque sensors, the robot is able to accurately estimate each load even with different loads at different locations.

In some embodiments, two adjacent joints of the robot may be equipped with six-degree-of-freedom force and torque sensors. Two adjacent joints (e.g., joints 125 and 126 in fig. 1) may be represented by joint N and joint (N +1), and the sensor readings on the corresponding joints may be

And

(converted to the same coordinates) they are all six degree of freedom vectors.

Is the total inertial force between the two joints. Assuming a single point contact is applied anywhere on a linking arm (e.g., linking arm 136 in fig. 1) between two joints, then the six-degree-of-freedom information of the point of contact (e.g., two-degree-of-freedom position on the linking arm, one-degree-of-freedom normal force, two-degree-of-freedom shear force, and one-degree-of-freedom torsional force) may be based on

Where T is the transfer function that solves the problem. This contact point information can be used for a variety of purposes, including better human-robot interface and security.

For example, the robot may have a better understanding of point contacts on its body, so that the robot can react more appropriately to ensureProtects the human operator and distinguishes abnormal collisions from normal interactive contact. In another example, a human operator may draw a particular pattern with a particular force profile on a particular connecting arm of the robot to give certain commands to the robot. On the basis of the preceding analysis, by projecting to the corresponding joint

The effect of point contact on adjacent joints can be calculated so that the local torque controller for each joint can generate additional torque to compensate for the effect. Thus, the entire arm may better resist interference on the arm without affecting the task and end effector.

In the above embodiments, a six degree of freedom force and torque sensor is utilized. In some examples of the invention, sensors capable of measuring force and torque information in fewer degrees of freedom may be used to detect simpler contact forces on the arm. For example, where the user only applies a normal force on the arm without shear or torsional friction, a four degree of freedom sensor that is unable to measure force and torsion along and about the arm axis may be used to sense contact force on the connecting arm.

Referring to fig. 1, in some embodiments, each of the

joints

121 and 127 of the robot 100 may be equipped with a multi-degree-of-freedom force and/or torque sensor, which in some aspect may be a six-degree-of-freedom force and torque sensor. In such an embodiment, additional redundant sensors in the arm may be fused together to improve sensing accuracy. For example, averaging sensor outputs in the same force direction from multiple joints of a fixed robotic arm may reduce the overall sensing error in that direction. If the sensor has noise or standard deviation of error σ in one sense direction, then when there are seven degree of freedom arms and six degree of freedom sensors in each joint, the standard deviation of error can become

Force and torque sensors in the joints can be used to accurately estimate the position, orientation of external contact forces on each of the robot connection arms 131-137And size, which is useful information for more advanced human-robot interactions and interfaces. Because the torque and force sensors do not have to be placed inside the

joints

131 and 137, they can be more flexibly mounted anywhere on the corresponding joint to obtain design benefits, such as simplifying wiring configurations or optimizing joint design for better dynamics and control performance.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the claimed invention to its fullest extent. The examples and embodiments disclosed herein are to be construed as merely illustrative and not a limitation of the scope of the present invention in any way. It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles discussed. In other words, various modifications and improvements of the embodiments specifically disclosed in the foregoing description are within the scope of the following claims. For example, any suitable combination of the features of the various embodiments described is contemplated.

Claims

1. A robotic arm, comprising:

a plurality of joints;

a plurality of connecting arms connected in sequence by the plurality of joints;

wherein at least two of the joints each include a sensor configured to measure force and torque information in more than one of six degrees of freedom (DOF) exerted on a respective one of the at least two joints.

2. A robotic arm as claimed in claim 1,

the sensor is a six degree of freedom force and torque sensor.

3. A robotic arm as claimed in claim 1,

each of the plurality of joints includes a sensor configured to measure force and torque information for more than one of six degrees of freedom applied to a respective one of the plurality of joints.

4. A robotic arm as claimed in claim 1,

the sensor is located between the input of a respective one of the at least two joints and a preceding one of the plurality of link arms.

5. A robotic arm as claimed in claim 4,

at least two of the joints each further comprise a sensor circuit board in communication with the sensor, and

wherein the sensor circuit board is located at the input end of a respective one of the at least two joints and adjacent to the sensor.

6. A robotic arm as claimed in claim 1,

the sensor is located between the output of a respective one of the at least two joints and a subsequent one of the plurality of link arms.

7. A robotic arm as claimed in claim 6,

at least two of the joints each further comprise an additional sensor, an

Wherein the additional sensor is located between the input of a respective one of the at least two joints and a preceding one of the plurality of link arms.

8. A robotic arm as claimed in claim 7,

the sensor and the additional sensor of each of the at least two joints are substantially identical.

9. A robotic arm as claimed in claim 1,

the sensor has a lower structural stiffness in the actuation direction of a respective one of the at least two joints than in the other directions.

10. A robotic arm as claimed in claim 9,

the sensor is configured to measure torque applied to a respective one of the at least two joints in the actuation direction and to measure force and torque information for at least one of the other five degrees of freedom applied to the respective one of the at least two joints.

11. A robotic arm as claimed in claim 1,

at least two of the joints are two adjacent joints of the plurality of joints.

12. A robot comprises a plurality of joints and a plurality of connecting arms which are sequentially connected through the joints,

wherein the plurality of joints each include sensors configured to measure force and torque information for more than one of six degrees of freedom (DOF) exerted on a respective one of the plurality of joints.

13. The robot of claim 12,

the sensor is configured to measure torque applied to a respective one of the plurality of joints and to measure force and torque information for at least one of the other five degrees of freedom applied to the respective one of the plurality of joints.

14. A robot as claimed in claim 13,

the sensor is located between the input and the output of a respective one of the plurality of joints.

15. A robot as claimed in claim 13,

the sensor is located between the input of a respective one of the plurality of joints and a preceding one of the plurality of link arms.

16. A robot as set forth in claim 15,

each of the plurality of joints further includes a sensor circuit board in communication with the sensor, and

wherein the sensor circuit board is located at the input end of a respective one of the plurality of joints and adjacent to the sensor.

17. A robot as claimed in claim 13,

the sensor is located between the output of a respective one of the plurality of joints and a subsequent one of the plurality of link arms.

18. A robot as set forth in claim 17,

each of the plurality of joints further comprises an additional sensor, and

wherein the additional sensor is located between the input of a respective one of the plurality of joints and a preceding one of the plurality of link arms.

19. A robot as claimed in claim 13,

the sensor is a six degree of freedom force and torque sensor.

20. A robot as set forth in claim 19,

the sensor has a lower structural stiffness in the actuation direction of a respective one of the plurality of joints than in other directions.