Multi-center impedance control

Abstract

A method of controlling a robot to perform complex assembly tasks such as inserting a component having a plurality of pins or bolts into a structure having a plurality of holes. The method uses an impedance controller including a plurality of reference centers having a set of gain coefficients. Only individual translational gain coefficients - one for spring force and one for damping force - are used without rotational gain. The method calculates individual spring-damping forces using gain values based on individual reference center positions and individual velocities, and measures contact forces and torques using sensors coupled between the robot arm and the manipulated component. Then, the calculated individual spring-damping forces are added to the measured contact forces and torques to provide a combined force and torque at the center of gravity of the component. Then, the impedance controller is used to calculate a new component pose based on the combined force and torque.

Description

Technical Field

[0001] The present disclosure relates to the field of industrial robot motion control, and more particularly, to a method for controlling a robot to perform complex assembly tasks such as inserting a double-pin component into a two-hole structure, the method including an impedance controller that uses a plurality of reference centers with a set of gains to add spring-damping forces calculated based on the respective reference center positions and velocities to measured contact forces and torques, and calculates a new component pose based on the summation. Background Art

[0002] It is well known to use industrial robots to repetitively perform a variety of manufacturing and assembly operations. However, some types of assembly operations - such as mounting a car door having two hinge pins onto a car body having two hinge pin holes - are still performed manually, where the machine lifts the weight of the door while a human operator aligns the respective hinge pins with the respective holes and lowers the door into place. This type of operation is still often performed manually because robots have difficulty detecting and correcting the complex misalignments that can occur when trying to insert multiple pins into multiple holes simultaneously.

[0003] In applications such as those discussed above, the prior art for controlling robots involves an impedance controller that uses a spring-damper system model with one reference center and defines two sets of gains, one linear and one angular. Then, the prior art attempts to compare the forces and torques fed back from the robot with the forces and torques calculated from the system model and adjust the robot position accordingly. However, in this traditional type of system model, adjustment of the gains is difficult; in particular, the angular gain, and its relationship to the linear gain, is non-intuitive. Additionally, a system model tuned for one component application is not applicable to another application with different component geometries or structural characteristics, so the gains and their relationships must be uniquely determined for each application.

[0004] In view of the above, there is a need for an improved impedance-based feedback control technique for robots performing alignment-sensitive assembly operations. Summary of the Invention

[0005] In accordance with the teachings of the present disclosure, a method for controlling a robot to perform complex assembly tasks is disclosed, where the complex assembly tasks are, for example, inserting a component having multiple pins or bolts into a structure having multiple holes. The method uses an impedance controller including multiple reference centers with a set of gain coefficients. Only individual translational gain coefficients are used - one for the spring force and one for the damping force - and there is no rotational gain. The method uses the respective gain values to calculate the spring-damping force based on the reference center position and velocity, and utilizes sensors coupled between the robot arm and the manipulated component to measure the contact force and torque. Then, the calculated spring-damping force is added to the measured contact force and torque to provide a combined force and torque at the center of gravity of the component. A new component attitude is then calculated based on the combined force and torque.

[0006] In conjunction with the accompanying drawings, additional features of the presently disclosed apparatus and methods will become apparent from the following description and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic diagram of a two-bolt workpiece installed in a two-hole structure and a conventional single-point impedance controller technique using translational and rotational gains, which is known in the art;

[0008] Figure 2 is a schematic diagram of a two-bolt workpiece installed in a two-hole structure and an impedance controller technique using two reference centers, according to an embodiment of the present disclosure;

[0009] Figure 3A 、 3B 、3C and 3D are schematic diagrams of steps involved in an impedance controller technique using two reference centers, according to an embodiment of the present disclosure, during the execution of Figure 2 as shown; and

[0010] Figure 4 is a flowchart of a method for controlling a robot performing an assembly task, according to an embodiment of the present disclosure, the method including a multi-reference center impedance controller. DETAILED DESCRIPTION

[0011] The following discussion of embodiments of the present disclosure for an impedance controller of a robot using multiple reference centers is exemplary in nature only and is in no way intended to limit the disclosed apparatus and techniques or their application or use.

[0012] It is well known to use industrial robots to repetitively perform a variety of manufacturing and assembly operations. However, some types of assembly operations - such as those where there is a large uncertainty in the initial part position, or those that are sensitive to even a small misalignment of one part relative to another - are difficult for a robot to perform reliably. Examples of these types of assembly operations include inserting an electronic component with multiple pins into a socket on a circuit board, and mounting a car door with two hinge pins onto a car body with two hinge pin holes. These types of operations are typically still performed manually because it is difficult for a robot to detect and correct the complexities caused by even a small misalignment that can occur when trying to insert multiple pins or bolts into multiple holes simultaneously.

[0013] Figure 1 is a schematic diagram of a two-bolt workpiece mounted in a two-hole structure and a conventional single-point impedance controller technique using translational and rotational gains, as known in the art. Assembly 100 includes door 110 and car body 120. Door 110 includes two vertically aligned bolts 112 and 114. Car body 120 includes vertically aligned holes 122 and 124. The job of a robot (not shown in the figure) is to manipulate door 110 to insert bolts 112 and 114 into holes 122 and 124, thereby forming a hinged connection of door 110 to car body 120. Of course, this assembly operation requires moving door 110 so that the ends of bolts 112 and 114 are aligned with and enter the tops of holes 122 and 124 simultaneously, and then lowering door 110 so that bolts 112 and 114 are fully inserted into holes 122 and 124.

[0014] In various applications such as Figure 1 the application shown, the prior art for controlling a robot involves using a spring-damper impedance controller model with one reference point or reference center 116, and defining two sets of gains - a set of translational gains and a set of rotational gains. Then, the prior art attempts to compare the forces and torques fed back from a force sensor 130 (coupled between the robot and door 110) with the forces and torques calculated from the spring-damper system model, and adjust the robot position accordingly. However, in this traditional type of system model, adjusting the gains is difficult; in particular, the rotational gains, and their relationship to the translational gains, are not intuitive. Additionally, the traditional single reference center impedance controller may be sensitive to the choice of the position of reference center 116.

[0015] In addition, a controller tuned to an application such as component 100 is not suitable for other applications where the component geometry or structural characteristics are different, so the gains and their relationships must be determined uniquely for each application. For example, if a spring-damper impedance controller has translational and rotational gains tuned to the door mounting operation of component 100, the same controller will not be properly tuned for the door mounting operation of component 140 where the hinge bolts are further spaced apart, or for the door mounting operation of component 150 where the hinge bolts are more closely spaced apart.

[0016] The present disclosure overcomes the limitations of single reference center impedance controllers by providing an impedance controller having multiple reference centers defined at multiple key points. Each reference center in the presently disclosed technology includes only translational spring-damper gains, and the same gain coefficients are used at all reference centers, which simplifies tuning and provides other benefits as described below.

[0017] Figure 2 is a schematic view of a two-bolt workpiece installed in a two-hole structure and an impedance controller technique using two reference centers according to an embodiment of the present disclosure. System 200 includes an industrial robot 202 tasked with mounting a vehicle door component 210 onto a vehicle body 220, similar to the example discussed previously and shown in Figure 1 FIG. The robot 202 typically communicates with the controller 204 via a cable but may be wireless, as is known in the art. The robot 202 can be a conventional multi-axis articulated industrial robot having multiple arms serially connected at rotational joints (as shown in simplified form in Figure 2 FIG.), or can be a "delta" type pick-and-place robot having multiple parallel linkages, or any other type of robot or machine capable of performing a specified movement of a workpiece based on instructions from the controller.

[0018] It should be emphasized that Figure 2 the door assembly operation in Figure 2 and the subsequent figures is merely an example of an assembly operation that is sensitive to even minor misalignments and can benefit from the impedance controller technology of the present disclosure. Those skilled in the art of assembly operations performed by robots can envision other examples, such as inserting a multi-pin electronic component into a circuit board or other component. In addition,

[0019] The door component 210 includes hinge bolts 212 and 214. The door component 210 has an analog center of gravity 211, which is a point defined based on the centers of gravity of bolts 212 and 214. The vehicle body 220 includes hinge holes 222 and 224. The task of the robot 202 is to manipulate the door component 210 to insert bolts 212 and 214 into holes 222 and 224 simultaneously, thereby creating a hinged connection of the door component 210 to the vehicle body 220. The robotic arm 230 represents the outer arm and wrist of the robot 202, where the arm 230 manipulates the vertical and horizontal positions and the tilt angle of the door component 210. The force and torque sensors 240 are coupled between the robotic arm 230 and the door component 210, and the sensors 240 provide force and torque signals to the controller 204 via a wired (shown) or wireless connection.

[0020] This disclosure describes impedance controller techniques using multiple reference centers. Impedance control is a method involving dynamic control of force and position. It is often used in applications where a manipulator interacts with its environment and the force-position relationship is of concern. Mechanical impedance is the ratio of force output to motion input. The "spring constant" defines the force output for the tension or compression of a spring. The "damping constant" defines the force output for a velocity input. The impedance of a control mechanism means the resistance to external motion imposed by the environment. Mechanical admittance is the reciprocal of impedance - it defines the motion generated by a force input. The key theory behind impedance control methods is to treat the environment as admittance and the manipulator as impedance. This disclosure describes an impedance controller method using multiple reference centers, which has advantages over prior art methods.

[0021] In the system 200, a reference center 216 is defined at the tip of bolt 212, and a reference center 218 is defined at the tip of bolt 214. The impedance controller defines spring-damping forces at each of the reference centers 216 and 218, including a displacement-based spring force and a velocity-based damping force. The spring force at the reference center 216 is calculated based on the displacement of the reference center 216 from a target reference point 226 at the bottom center of the hole 222. Similarly, the spring force at the reference center 218 is calculated based on the displacement of the reference center 218 from a target reference point 228 at the bottom center of the hole 224.

[0022] The following is a discussion of how the spring-damping forces at the reference centers 216 and 218 are calculated in the impedance controller of this disclosure. The position of the reference center 216 is designated as p 216 , and the position of the reference center 218 is designated as p 218 . The position p 216 and p 218 have three-dimensional (e.g., X, Y, and Z) coordinates. The velocity of the reference center 216 is designated as v 216 , and the velocity of the reference center 218 is designated as v218 The velocity v 216 and v 218 are vectors having three-dimensional (X, Y, and Z) components. The position p 216 and p 218 as well as the velocity v 216 and v 218 are calculated by the controller 204 based on the known geometry of the robot 202 including the position and orientation of the arm 230 and the geometry of the door member 210.

[0023] The position of the target reference point 226 is designated as p 226 , and the position of the target reference point 228 is designated as p 228 . The position p 22 6 and p 228 also have three-dimensional (X, Y, and Z) coordinates, where at least the lateral and vertical components are fixed relative to the base of the robot 202. Additionally, although Figure 2 represents a static image of the components in the system 200, it should be noted that the techniques of the present disclosure can be applied while the vehicle body 220 is moving along the conveyor, and the longitudinal (Z-direction) velocity of the conveyor is taken into account in the three-dimensional movement of the robot arm 230.

[0024] According to the impedance controller of the present disclosure, the spring-damping force at the reference center 216 is calculated as:

[0025] f 216 = K p (p 226 - p 216 ) - D p (v 216 ) (1)

[0026] Similarly, the spring-damping force at the reference center 218 is calculated as:

[0027] f 218 = K p (p 228 - p 218 ) - D p (v 218 ) (2)

[0028] where K p is the spring constant or gain coefficient, D p is the damping constant or gain coefficient, and the other variables are defined as above. The same spring gain coefficient K p and the same damping gain coefficient D p, and these coefficients can be determined empirically and finely adjusted as needed to achieve optimal controller results. Since the multi-reference center impedance controller does not use rotational gain coefficients, the translational gain coefficients selected for a particular application (such as door mounting) may be very effective for other applications of the same type with different component geometries. Using a single set of gain coefficients without rotation constitutes a major advantage of this multi-center impedance controller over the prior art.

[0029] Equation (1) can be interpreted as follows: The spring force at the reference center 216 is the spring constant multiplied by the displacement (position difference) of the reference center 216 from the target reference point 226, and the damping force at the reference center 216 (subtracted from the spring force) is the damping constant multiplied by the velocity of the reference center 216. Equation (2) is interpreted similarly. The spring-damping forces at the reference centers 216 and 218 are three-dimensional force vectors.

[0030] Figure 3A , 3B , 3C and 3D are schematic diagrams of the steps involved in the impedance controller technique using two reference centers according to an embodiment of the present disclosure during the execution Figure 2 shown. Figure 3A shows the first step in the process, which is the calculation of the spring-damping forces at the reference centers 216 and 218 as described above. In Figure 3A , the force vector 310 represents f (calculated in Equation (1)) 216 , and the force vector 312 represents f (calculated in Equation (2)) 218 . The calculation of the spring-damping forces at this first step is performed by the controller 204 based on the predetermined values of K p and D p and the reference center positions and velocities known to the controller 204 as described above.

[0031] Figure 3B shows the second step in the process, where the combined contact force and torque are measured by the sensor 240. The force vector 320 represents the force measured by the sensor 240, and the torque vector 322 represents the torque measured by the sensor 240. The force vector 320 and the torque vector 322 respectively represent the force and torque applied by the door component 210 on the robotic arm 230. The values of the force vector 320 and the torque vector 322 are provided to the controller 204 as sensor signals from the sensor 240.

[0032] Figure 3C shows the third step in the process, where the controller 204 calculates the spring-damping forces at the reference centers 216 and 218 (from Figure 3A ) and (from Figure 3BThe sum of the contact forces and torques measured by sensor 240. Summing the respective force vectors and torques about the center of gravity 211 results in a resultant force vector 330 and a resultant torque vector 332 applied at the center of gravity 211.

[0033] Figure 3D Illustrates the fourth step in the process, where the controller 204 calculates the new pose of the door component 210 under the action of the forces and torques (resultant force vector 330 and resultant torque vector 332) from the third step. Using known impedance controller techniques, the controller 204 solves equations of the type for a spring - mass - damper system, i.e., F = ma + Cv + Kx + S. However, since the spring force and the damping force are already included in the calculated force F, the equations simplify to F = ma for translational motion and T = Iα for rotational motion. Utilizing the known mass and inertia characteristics of the door component 210, the controller 204 determines the motion of the door component 210 that will be produced by the resultant force vector 330 (F) and the resultant torque vector 332 (T). Then, the controller 204 moves the robotic arm 230 via the robot 202 such that the door component 210 undergoes the just - calculated motion. This motion is shown in Figure 3D where the door component 210 has rotated (arrow 340) to become more closely aligned with the holes 222 and 224 and has translated (arrow 342) to become almost fully inserted into the holes 222 and 224.

[0034] The multi - center impedance controller discussed above with reference to the door - mounting example has several advantages over the prior - art single - center impedance controller. First, in a multi - center controller, the selection of the respective reference centers and their corresponding target points is intuitive and straightforward. In the case of inserting a multi - bolt component into corresponding holes, the respective tips of the individual bolts can be easily defined as the reference center points. Additionally, the multi - center controller eliminates the need for a rotational gain coefficient, the determination of which is difficult and non - intuitive. Further, a set of spring and damping gain coefficients is used at all (two or more) reference centers, and the individual gain coefficients used in one application of the multi - center controller can be applied to other applications of similar components with different geometries.

[0035] Figure 4 is a flow chart 400 of a method for controlling a robot performing an assembly task, the method including a multi - reference - center impedance controller. In Figure 4 the assembly operation described in the method includes using the robot 202 (with an external robotic arm 230) to simultaneously insert a plurality of pins or bolts of a first workpiece 210 into a plurality of cavities of a second workpiece 220, as shown in Figure 2 and 3. However, as described above, the multi - reference - center impedance controller of the present disclosure can also be applied to other types of assembly operations.

[0036] At block 402, reference points are defined at the tip of each of the respective pins on the first workpiece 210, and corresponding target points are defined in the cavities of the second workpiece 220. Each of the respective pins corresponds to a specific cavity in the respective cavities, and accordingly defines a reference point to target point relationship. At block 404, the robot controller 204 calculates the spring-damping force at the reference point based on the velocity of each reference point and the displacement of the reference point relative to the corresponding target point. Specifically, the spring-damping force at the first reference point is calculated using the above equation (1) and the like. The controller 204 knows the reference point position and velocity based on robot kinematics and workpiece geometry. The spring gain coefficient K p and the damping gain coefficient D p can be determined empirically and fine-tuned as needed to achieve optimal controller results, and the same spring gain coefficient and damping gain coefficient are used to calculate the spring-damping force for each of the respective reference points.

[0037] At block 406, the contact force and torque are measured by the sensor 240 coupled between the robot 202 and the first workpiece 210, and the contact force and torque are transmitted to the controller 204. At block 408, the controller 204 calculates the resultant force and torque at the center of gravity 211 as the sum of the respective spring-damping forces (block 404) and the contact force and torque (block 406). Summing the force vectors 310 and 312, the force vectors 320 and torque 322 about the center of gravity 211 results in a resultant force vector 330 and a resultant torque vector 332 applied at the center of gravity 211.

[0038] At block 410, the controller 204 calculates the new pose of the door component 210 based on the resultant force 330 and torque 332. The new pose of the door component 210 is calculated using the F = ma and T = Iα equations. At block 412, in response to a signal from the controller 204, the robot 202 moves the door component 210 to the new pose (calculated at block 410). The impedance controller of the present disclosure is implemented as a real-time feedback control system, which means that after moving the door component 210 to the new pose at block 412, the process continuously loops back to block 404 to calculate a new spring-damping force. This loop continues until the bolts 212 and 214 of the door component 210 are fully seated in the holes 222 and 224 of the vehicle body 220.

[0039] Again, for clarity, the foregoing discussion of a door component having hinge pins being installed in corresponding hinge holes is merely an example. The disclosed techniques can be applied to any type of workpiece having multiple pins to be inserted into corresponding holes simultaneously, or other types of assembly activities that are sensitive to even minor misalignments.

[0040] Throughout the foregoing discussion, various computers and controllers have been described and implied. It should be understood that the software applications and modules of these computers and controllers are executed on one or more computing devices having a processor and a memory module. In particular, this includes the processor in the robot controller 204 discussed above. Specifically, the processor in the controller 204 is configured to use impedance feedback control techniques with multiple reference centers in the manner discussed above.

[0041] As described above, the disclosed technique of using an impedance controller with multiple reference centers for a robot improves the performance of robot assembly operations where there is a large amount of uncertainty in the part positions or the assembly operations are sensitive to even a slight misalignment of one part relative to another part.

[0042] Although multiple exemplary aspects and embodiments of using an impedance controller with multiple reference centers for a robot have been discussed above, those skilled in the art will recognize its modifications, permutations, additions, and sub-combinations. Accordingly, the appended claims below and the claims introduced hereafter are intended to be construed to include all such modifications, permutations, additions, and sub-combinations in their true spirit and scope.

Claims

1. A method for controlling a robot that performs an assembly operation of inserting a plurality of pins of a first workpiece into a plurality of cavities of a second workpiece, the method comprising: Defining a reference point at the tip of each of the plurality of pins on the first workpiece, and defining a corresponding target point for each reference point in the cavity of the second workpiece; Calculating a spring-damping force at each reference point by a robot controller based on the velocity of each reference point among the respective reference points and the displacement of the reference point relative to the corresponding target point; Measuring a contact force and a torque by a sensor coupled between the robot and the first workpiece, and transmitting the contact force and the torque to the controller; Calculating, by the controller, a resultant force and torque that are a synthesis of the respective spring-damping forces and the contact force and torque; Calculating, by the controller, a new attitude of the first workpiece based on the resultant force and torque; And Moving the first workpiece to the new attitude by the robot in response to a signal from the controller; wherein a single damping gain coefficient and a single spring gain coefficient are used when calculating the spring-damping forces at all the respective reference points; and The damping gain coefficient and the spring gain coefficient are translational gain coefficients, and no rotational gain coefficient is used when calculating the spring-damping forces at the respective reference points.

2. The method according to claim 1, wherein, Calculating the spring-damping force at each of the respective reference points as the damping gain coefficient multiplied by the velocity of the reference point plus the spring gain coefficient multiplied by the displacement of the reference point relative to the corresponding target point.

3. The method according to claim 1, wherein, Using kinematic calculations to determine the velocities of the respective reference points and the displacements of the respective reference points relative to the corresponding target points, the kinematic calculations being based on known robot positions and velocities and the known geometry of the first workpiece relative to the robot.

4. The method according to claim 1, wherein, Calculating the resultant force and torque that are a synthesis of the respective spring-damping forces and the contact force and torque includes adding all the respective spring-damping forces and the contact force and torque about the simulated center of gravity of the first workpiece.

5. The method according to claim 1, wherein Calculating the new attitude of the first workpiece includes using an impedance controller to calculate the new attitude of the first workpiece based on the resultant force and torque applied at the simulated center of gravity of the first workpiece.

6. The method according to claim 1, wherein, The first workpiece is a door component, and the second workpiece is a vehicle body.

7. The method according to claim 6, wherein, The plurality of pins are two hinge pins on the door component, and the assembly operation is simultaneously inserting the two hinge pins into two hinge openings on the vehicle body.

8. The method according to claim 6, wherein, During the assembly operation, the vehicle body is moving on a conveyor, and the robot controller includes the movement of the conveyor in the signal sent to the robot to move the door component.

9. A method for controlling a robot to mount a door component on a vehicle body by inserting two hinge pins on the door component into two hinge openings on the vehicle body, the method comprising: Reference points are defined at the ends of each of the two hinge pins on the door member, and corresponding target points for each reference point are defined in each of the two hinge openings on the vehicle body; The robot controller calculates the spring-damping force at each reference point based on the velocity of each reference point and the displacement of the reference point relative to the corresponding target point; The contact force and torque are measured by a sensor coupled between the robot and the door member, and the contact force and the torque are transmitted to the controller; The controller calculates the resultant force and torque as the sum of the respective spring-damping forces and the contact force and torque about the center of gravity of the two hinge pins on the door member; The controller uses an impedance controller to calculate a new attitude of the door member based on the resultant force and torque; And In response to a signal from the controller, the robot moves the door member to the new attitude; wherein, when calculating the spring-damping forces at the two reference points, one damping gain coefficient and one spring gain coefficient are used, and the damping gain coefficient and the spring gain coefficient are translational gain coefficients.

10. The method according to claim 9, wherein, The spring-damping force at each reference point is calculated as the damping gain coefficient multiplied by the velocity of the reference point plus the spring gain coefficient multiplied by the displacement of the reference point relative to the corresponding target point.

11. A system for performing an assembly operation of inserting a plurality of pins of a first workpiece into a plurality of cavities of a second workpiece, the system comprising: An industrial robot configured to move the first workpiece; A force and torque sensor coupled between the first workpiece and the robot; And A robot controller having a processor and a memory, the controller communicating with the robot and receiving signals from the sensor, the controller being configured to perform steps including the following; Reference points are defined at the tips of each of the plurality of pins on the first workpiece, and corresponding target points for each reference point are defined in the cavities of the second workpiece; Based on the velocity of each reference point and the displacement of the reference point relative to the corresponding target point, the spring-damping force at the reference point is calculated; Calculate the resultant force and torque as the sum of the respective spring-damping forces and the contact force and torque measured by the sensor; Calculate a new attitude of the first workpiece based on the resultant force and torque; And Send a signal to the robot to cause the robot to move the first workpiece to the new attitude; wherein, when calculating the spring-damping forces at all the respective reference points, one damping gain coefficient and one spring gain coefficient are used, and wherein each gain coefficient is a translational gain coefficient.

12. The system according to claim 11, wherein, The spring-damping force at each of the respective reference points is calculated as the damping gain coefficient multiplied by the velocity of the reference point plus the spring gain coefficient multiplied by the displacement of the reference point relative to the corresponding target point.

13. The system according to claim 11, wherein, Kinematics calculations are used to determine the velocities of the respective reference points and the displacements of the respective reference points relative to the corresponding target points, the kinematics calculations being based on the known position and velocity of the robot and the known geometry of the first workpiece relative to the robot.

14. The system according to claim 11, wherein Calculating the forces and torques that are the sum of the respective spring-damping forces and the contact forces and torques includes adding all of the respective spring-damping forces and the contact forces and torques about the simulated center of gravity of the first workpiece.

15. The system according to claim 11, wherein, Calculating the new pose of the first workpiece includes using an impedance controller to calculate the new pose of the first workpiece based on the combined forces and torques applied at the simulated center of gravity of the first workpiece.

16. The system according to claim 11, wherein, The first workpiece is a door component and the second workpiece is a vehicle body, and wherein the plurality of pins are two hinge pins on the door component, and the assembly operation is inserting the two hinge pins simultaneously into two hinge openings in the vehicle body.

17. The system according to claim 16, wherein, During the assembly operation the vehicle body is moving on a conveyor, and the robot controller includes the motion of the conveyor in the signal to the robot to move the door component.

Images