Method for calibrating torque sensor in robot joint
By using weighted components and sensors to measure torque values in robot joints, calculating torque reference values, and calibrating torque sensors using correction functions, the problem of decreased accuracy of robot joint torque sensors is solved. This achieves efficient calibration without disassembly, improving robot safety and accuracy.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-19
- Publication Date
- 2026-03-27
AI Technical Summary
In existing technologies, the accuracy of torque sensors on robot joints decreases over time, leading to a decline in robot performance and posing safety hazards. Furthermore, recalibration requires disassembling the robot, which is a labor-intensive process.
By using a weighted mass component to load the end effector in the robot joint, the weight is determined by a force sensor, and the torque value is measured by combining a rotational position sensor and a torque sensor. The torque reference value is calculated, and the torque sensor is calibrated by a correction function, thus avoiding the need to disassemble the robot.
This enables efficient calibration of torque sensors without disassembly during robot operation, saving time and labor costs while improving safety and accuracy.
Smart Images
Figure CN121752397A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for calibrating a torque sensor in a robot joint of a robot having one or more robot joints, each comprising a torque sensor and a rotational position sensor. BACKGROUND
[0002] Robots are increasingly used in production plants as the degree of industrial automation increases. Many such robots have robot joints that are rotatable to achieve motion, for example, about multiple spatial axes. In addition to drive motors and gear stages, sensor technology, such as torque sensors, is also applied in the context of robot joints. Torque sensors are typically calibrated during the manufacturing phase.
[0003] The functionality, in particular the accuracy, of such torque sensors can deteriorate over time, for example, due to wear. A decrease in sensor accuracy can lead to a decrease in robot performance and can endanger operational safety. Therefore, it is common practice in the prior art to disassemble the robot during maintenance or when a sensor accuracy problem is detected. The torque sensor can be removed from the robot and recalibrated externally. The recalibration of the torque sensor thus requires a large amount of effort. SUMMARY
[0004] Against this background, it is an object of the present invention to reduce the effort required for calibrating a torque sensor arranged in a robot joint.
[0005] This object is achieved by a method for calibrating a torque sensor in a robot joint of a robot having one or more robot joints, each comprising a torque sensor and a rotational position sensor, the method having the following method steps: A. loading an end effector of the robot with a mass having a weight; B. determining the weight of the mass on the end effector by means of a force sensor; C. measuring a torque measurement value by means of the torque sensor to be calibrated; D. determining a respective rotational position of the robot joint by means of one or more rotational position sensors; E. calculating a torque acting on the robot joint whose torque sensor is to be calibrated as a torque reference value on the basis of the determined weight and the determined rotational position of the robot joint wherein the method steps A, B, C, D and E are optionally repeated one or more times while the position of the robot is changed, wherein a correction function for correcting a torque measured by the torque sensor to be calibrated is determined by means of a torque measurement value or a plurality of torque measurement values and a torque reference value or a plurality of torque reference values.
[0006] The robot calibrated using the method according to the application comprises at least one torque sensor and at least one rotational position sensor in at least one robot joint. Furthermore, such a robot has an end effector, i.e. an effector arranged on a robot arm at the distal end. According to the application, the end effector of the robot is loaded with a weight. The weight is determined by means of a force sensor. The weight acting on the robot tends to set one or more robot arms in motion. In order to maintain the static equilibrium of the robot, torques have to be provided in each of the robot joints. These torques acting on the robot joints are measured as torque values by means of one or more torque sensors, which are calibrated for each robot joint. The torque measurement values can be temporarily stored in a storage unit of the robot for possible future operation. Furthermore, according to the application, the current rotational position of the robot joint is detected by one or more rotational position sensors. Furthermore, the rotational position of the robot joint can be used, in combination with geometrical information, for example the length of the individual robot arm sections, to calculate the position coordinates of the end effector. Furthermore, according to the application, a torque reference value is calculated for each robot joint or torque sensor on the basis of the determined weight and the determined rotational position of the robot joint. The aforementioned method steps can be repeated with each change in the position of the robot or robot arm section for the optimized calibration of the torque sensors. Finally, a correction function is determined by means of the torque measurement value or values and the torque reference value or values. The torque sensors are calibrated using the correction function. The aim of determining the correction function is to minimize any differences, deviations or errors between the measured torque values and the calculated torque reference values, for example using linear regression.
[0007] An advantage of the method according to the application is that the torque sensors do not have to be disassembled and thus temporarily shut down for calibration. The calibration can be carried out during the manufacturing process or during operation of the robot. Furthermore, the calibration can be carried out, for example, at regular intervals during operation of the robot and in particular after a certain operating time, for which wear is expected thereafter. Overall, resources such as time, labor and thus costs can thus be saved.
[0008] For increased safety, a redundant sensor arrangement can optionally be provided, in particular a plurality of torque sensors and a plurality of rotational position sensors can be provided for each robot joint. In particular, the robot joint can have one rotational degree of freedom, i.e. can be designed to rotate about exactly one axis.
[0009] The correction function can be linear or non-linear. The correction function can comprise a plurality of free parameters, wherein the number of repetitions of the method steps A to E must be greater than the number of free parameters of the correction function. Furthermore, the correction function can be determined by adjusting the parameters of an already existing correction function.
[0010] In a preferred embodiment of the application, it is provided that the torque sensors of a plurality of robot joints, preferably of all robot joints, of the robot are calibrated simultaneously. Simultaneously calibrating a plurality of torque sensors is advantageous, because the total number of robot positions can be reduced during the execution of the calibration method according to the application.
[0011] According to an advantageous embodiment of the application, it is provided that the Jacobian matrix is determined on the basis of the rotational position of the robot joint, which indicates the distribution of the torque in the robot joint to the weight of the mass on the end effector. The Jacobian matrix is specific to the robot and to the situation. The Jacobian matrix also depends on the rotational position of the robot joint. The Jacobian matrix can also include force components, in particular the own weight of the robot, and thus also the moments of inertia of the robot or individual robot components, such as robot arm segments. Alternatively, the weight of the robot can be taken into account as an additional mathematical expression when calculating the torque.
[0012] In a preferred embodiment of the application, it is provided that the end effector comprises a force sensor. The force sensor is preferably designed as a three-axis sensor, so that forces in all three spatial directions can be determined. By incorporating the force sensor into the end effector, a space-saving and thus compact design can be achieved. The end effector can comprise a plurality of force sensors. In addition, one or more further force sensors can be arranged on the robot, in particular in the robot joint or on the robot arm segment, in particular for detecting the inertial forces generated by the own weight of the robot, the robot arm segments or the robot joints of the robot.
[0013] According to a preferred embodiment of the application, the force sensor is connected to the mass. The force sensor or one of the force sensors can preferably comprise or be designed as an acceleration sensor and thus detect centrifugal forces, in particular centrifugal forces acting on the mass. This offers the advantage that the forces actually acting on the mass, and thus also on the robot, can be determined more precisely.
[0014] According to an advantageous embodiment of the application, it is provided that the end effector is designed as a gripper. The end effector or gripper can have a plurality of movable gripping fingers for easily and safely gripping mass of different sizes.
[0015] It is provided in a preferred embodiment of the application that the torque reference values calculated during the repeated method steps A, B, C, D and E are weighted differently. Since the robot can perform a regular motion, certain rotational positions of the robot joints and positions of the robot can be more important during operation than other rotational positions of the robot joints and positions of the robot. When calculating the torque reference values, the repeated method steps A, B, C, D and E can be weighted more heavily in the more significant rotational positions and positions.
[0016] It is a further object of the application the use of the method according to any of the preceding embodiments for calibrating a torque sensor in a robot joint of a robot in an assembled and functional state of the robot, preferably during operation of the robot. The same advantages and technical effects as already explained in the description of the application and its embodiments apply to the use of the method according to the application. BRIEF DESCRIPTION OF DRAWINGS
[0017] Further details and advantages of the application will be explained below with reference to exemplary embodiments shown in the drawings. In the drawings: Figure 1 A first exemplary embodiment of a robot is shown schematically in a side view to illustrate an exemplary embodiment of the method according to the application; Figure 2a A second exemplary embodiment of a robot is shown schematically in a side view to illustrate an exemplary embodiment of the method according to the application; Figure 2b A second exemplary embodiment of a robot is shown schematically in a side view to illustrate an exemplary embodiment of the method according to the application; Figure 2a A second exemplary embodiment of a robot is shown schematically in a side view to illustrate an exemplary embodiment of the method according to the application; DETAILED DESCRIPTION
[0018] Figure 1 A robot 1 is shown schematically in which the method according to the application can be applied. The robot 1 has a plurality of robot joints 3. The robot joints 3 each comprise a torque sensor 3.1 and a rotational position sensor 3.2. By means of the robot joints 3, the robot 1 can be moved along and about all three spatial axes and, in particular, can also be rotated about a vertical axis V. Figure 1 The robot 1 in the first exemplary embodiment shown in Fig. 1 also has a seventh axis L along which the robot 1 is designed to be able to move translationally.
[0019] The robot 1 has an end effector 5 which is designed schematically as a gripper or pincer-like device. In a first method step, a mass m with a weight of G is placed on the end effector 5 (in Figure 1The weight is determined by means of a force sensor 7 incorporated into the end effector 5. Then, torque measurement values are measured by each of the torque sensors 3.1 to be calibrated arranged in all robot joints 3. At the same time or subsequently, the rotational positions of the robot joints 3 are determined by the rotational position sensors 3.2. Then, based on the weight G determined by the force sensor 7 and the determined respective rotational positions of the robot joints 3, a torque reference value is calculated for each robot joint 3, which acts on the respective robot joint 3. The previously performed set of method steps is repeated several times, wherein the position of the robot 1, i.e. the rotational positions of the robot joints 3, is changed after each set. Since different robot joints 3 can have experienced different degrees of wear or the torque sensors 3.1 can have different levels of accuracy for other reasons, a correction function is determined for each robot joint 3 by means of the plurality of torque measurements and the plurality of torque reference values in order to correct the torque measured by the torque sensor 3.1 to be calibrated.
[0020] Figure 2a A second exemplary embodiment of the robot 1 is shown schematically in a side view to illustrate an exemplary embodiment of the method according to the application. In Figure 2a , a mass piece m held by the end effector 5 is visible. Furthermore, in Figure 2a , the robot 1 is illustrated in a first motion state, i.e. in particular the robot joints 3 each have a certain rotational position, e.g. a and β. From the first motion state of the mass piece m with a weight of G, certain forces acting on the robot 1 arise, e.g. F1, F2 and F3. A torque reference value can be calculated for each robot joint 3 in dependence on all forces acting on the robot 1 in combination with the first motion state, in particular the rotational positions of the robot joints and the lengths of the robot arm sections 1.1. By means of the calculated plurality of torque reference values for each robot joint 3 and the measured torque measurement values for each robot joint 3, a correction function can be determined to correct the torque measured by the torque sensor 3.1 to be calibrated.
[0021] Figure 2b A second exemplary embodiment from Figure 2a in a changed position of the robot 1 is shown schematically. In other words, the robot 1 is illustrated in a second motion state. In particular, the robot joints 3 each have a different rotational position. Furthermore, the robot 1 can be loaded with a different mass piece having a different weight compared to the mass piece m with the weight G from Figure 2a . This results in other forces F i , in particular Figure 2bthe forces F4, F5 and F6 in the coordinate system of the robot 1. Due to the varying forces F4, F5 and F6, the torque reference values for each robot joint 3 vary. According to the application, the motion state of the robot 1 can be changed multiple times, in particular arbitrarily, in order to determine an improved correction function.
[0022] List of reference signs 1 robot 3 robot joint 3.1 torque sensor 3.2 rotational position sensor 5 end effector 7 force sensor a, β rotational position of each robot joint m mass G weight of the mass m F i force acting on the robot V vertical axis L linear axis
Claims
1. A method for calibrating torque sensors in the robot joints (3) of a robot (1) having one or more robot joints (3), each of the one or more robot joints including a torque sensor (3.1) and a rotational position sensor (3.2), the method comprising the following steps: A. Load the end effector (5) of the robot (1) with a mass component of a certain weight; B. The weight of the mass on the end effector (5) is determined by means of a force sensor (7); C. The torque measurement value (M) is measured using the torque sensor (3.1) to be calibrated. m ); D. The corresponding rotational position of the robot joint (3) is determined by means of one or more of the rotational position sensors (3.2); E. Based on the determined weight and the determined rotational position of the robot joint (3), the torque is calculated as a torque reference value (M). ref The torque is applied to the robot joint (3) to be calibrated by its torque sensor (3.1). Among them, method steps A, B, C, D and E may be repeated once or multiple times when the position of the robot (1) changes. Among them, by means of a torque measurement value (M) m ) or multiple of the torque measurements (M) m ) and a torque reference value (M) ref ) or multiple of the aforementioned torque reference values (M ref ) determines the correction function used to correct the torque measured by the torque sensor (3.1) to be calibrated.
2. The method according to claim 1, characterized in that, The torque sensors (3.1) of the robot (1) at multiple robot joints (3), preferably all robot joints, are simultaneously calibrated.
3. The method according to any one of the preceding claims, characterized in that, A Jacobian matrix is determined based on the rotational position of the robot joint (3), the Jacobian matrix indicating the distribution of torque in the robot joint (3) to the weight of the mass on the end effector (5).
4. The method according to any one of the preceding claims, characterized in that, The end effector (5) includes the force sensor (7).
5. The method according to any one of the preceding claims, characterized in that, The force sensor (7) is connected to the mass component.
6. The method according to any one of the preceding claims, characterized in that, The end effector is designed as a gripper.
7. The method according to any one of the preceding claims, characterized in that, The torque reference values calculated during the repetition of steps A, B, C, D, and E of the method are weighted differently.
8. The use of the method according to any one of the preceding claims for calibrating a torque sensor (3.1) in a robot joint (3) of a robot (1) in an assembled and functional state, preferably during operation of the robot (1).