Fast settling for robotic motion control

Abstract

To reduce tool jerk and thus reduce the robot stabilization time.SOLUTION: Provided are a system and method for controlling movement of a robot holding a tool from an end of one tool operation to a beginning of a next tool operation. The method includes: separating the robot movement into a plurality of segments that have different robot movement accelerations; determining an optimal acceleration of the robot for each segment that optimizes a cycle time of the robot movement; and reducing the optimal acceleration of the robot during a last segment so as to reduce tool jerk when the robot reaches the beginning of the next tool operation. In one non-limiting embodiment, the tool is a laser cutting tool and the number of segments is seven.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 63 / 596,372, entitled Rapid Settling for Robot Motion Control, filed on November 6, 2023.

Background Art

[0002] The present disclosure generally relates to systems and methods for reducing the settling time of a robot holding a tool at a robot movement destination, and more particularly to systems and methods for reducing the settling time of a robot holding a tool at a robot movement destination, including reducing the acceleration of the robot only during the last segment of the movement operation.

[0003] Description of Related Art Robots perform multiple tasks. One of those tasks is laser cutting of various parts. From an efficiency perspective, it is desirable to minimize the cycle time of the cutting operation. Therefore, robot laser cutting typically requires aggressive robot motion, for example, from the end of one cutting operation to the start of the next, to optimize the cycle time of the cutting operation. This aggressive robot motion often results in excessive vibration of the robot cutting tool at the stop position where the next cutting operation is initiated, which is referred to herein as jerk of the tool. This tool jerk directly affects the quality of the cutting and thus the shape of the part. Therefore, it is often necessary to provide a settling time for the tool such that the tool jerk decreases to an acceptable level when the tool reaches the stop position before the next cutting operation is initiated. This undesirably increases the cycle time of the cutting operation.

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is known to reduce the moving speed of a cutting tool during robot movement from the end of one cutting operation to the start of the next cutting operation, to reduce the vibration of the tool at the stop position, and thus to reduce the time required for tool setting. However, if the speed of the robot is slowed down during robot movement, the cycle time of the cutting operation is extended. Furthermore, since the time for tool setting and stabilization may vary for different parts, these movement operations require cycle tuning, which requires a longer robot teaching time.

[0005] Stated differently, labor-intensive and iterative techniques are sometimes employed to optimize the movement pattern of the robot for each of the robot's cutting operations. The total part processing time is equal to the robot's movement time plus the delay time added considering the setup time or setting time and the cutting time. There is a balance between the programmed slowdown of the movement time and the delay that poses the challenge of finding the optimal performance, which requires specialized technicians or programmers, resulting in increased costs.

Means for Solving the Problem

[0006] Summary In the following, a system and a control method for controlling the movement of a robot holding a tool from the end of one tool operation to the start of the next tool operation are disclosed and described that reduce the tool jerk and thus reduce the stabilization time of the robot. This control method separates the movement of the robot into a plurality of robot movement segments having different robot movement accelerations, determines the optimal acceleration of each robot for the robot movement segment that optimizes the cycle time of the robot operation, and further reduces the optimal acceleration of the robot in the last robot movement segment so as to reduce the tool jerk when the robot reaches the start of the next tool operation. In a non-limiting embodiment, the tool is a laser cutting tool and the number of segments is seven segments.

[0007] Additional features of the present disclosure will become apparent from the following description in connection with the accompanying drawings and the appended claims.

Brief Description of the Drawings

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Figure 1

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Figure 2

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Modes for Carrying Out the Invention

[0014] The following embodiments of the present disclosure relating to a system and a control method for reducing the setting time of a robot that holds a tool at a movement destination of the robot are merely exemplary and do not limit the present disclosure, its applications, and its use. For example, in this disclosure, the tool is described as a laser cutting tool, but other types of tools may be used.

[0015] FIG. 1 is a diagram showing a robot system 10 including a six-axis robot 12 that holds a cutting tool 14 that performs a cutting operation on a component 16. The robot 12 is intended to represent any robot suitable for the purposes described herein. The control unit 18 controls the robot 12 and is intended to represent all of the control units and devices necessary to perform various calculations and control the robot 12 as described herein.

[0016] FIG. 2 is a graph showing the relationship between time on the horizontal axis and the position of the robot, the speed of the robot, the acceleration of the robot, and the jerk of the tool on the vertical axis, and shows the robot motion profile and profile characteristics of the robot 14 using an S-curve. This robot motion profile is intended to represent the optimal speed that the tool 14 can form from the position at the end of one cutting operation to the stop position at the start of the next cutting operation, which may be called an air cut. This robot motion profile typically causes high tool vibration or tool jerk at the end of the motion cycle, which requires a setting time to stabilize the tool 14 before the cutting operation proceeds.

[0017] The S-shaped robot motion profile shown in FIG. 2 can be divided into seven segments, namely, a first segment between time 0 and time Ts1 at the end position of the last cutting operation, which is 1 second in this example, a second segment between time Ts1 and time Ts2, which is 2 seconds in this example, a third segment between time T2 and time Ts3, which is 1 second in this example, a fourth segment between time Ts3 and time Ts4, which is 2 seconds in this example, a fifth segment between time Ts4 and time Ts5, which is 1 second in this example, a sixth segment between time Ts5 and time Ts6, which is 2 seconds in this example, and a seventh segment between time Ts6 and time T, which is 1 second in this example. This particular robot movement takes 10 seconds. However, other robot movement operations take different times but can also be divided into 7 segments.

[0018] The graph line 20 of the position shows the position of the tool 4 from the end position of the last cutting operation at time 0 to the start position of the next cutting operation at time 10 seconds.

[0019] The graph line 22 of the speed shows that the robot 12 has an increasing speed from 0 seconds to about 4 seconds during the first three segments, then has a constant speed for about 2 seconds, and decelerates during the last 4 seconds of the last three segments until it stops at time 10 seconds.

[0020] The graph line 24 of the acceleration shows the acceleration of the robot 12 that provides the robot speed profile of the graph line 22. In particular, the robot acceleration increases from 0 seconds to 1 second during the first segment, then the robot acceleration is constant from 1 second to 3 seconds during the second segment, then the robot acceleration decreases from 3 seconds to 4 seconds during the third segment, then the robot acceleration is constant from 4 seconds to 6 seconds during the fourth segment, then the robot acceleration decreases from 6 seconds to 7 seconds during the fifth segment, then the robot acceleration is constant from 7 seconds to 9 seconds during the sixth segment, and then the robot acceleration increases from 9 seconds to 10 seconds during the seventh segment.

[0021] The graph line 26 of the tool jerk indicates the magnitude of the tool jerk corresponding to the change in the acceleration of the robot 12. The slope of the graph line 24 determines the magnitude of the graph line 26. The acceleration of the robot provides positive jerk, and the deceleration of the robot provides negative jerk. Based on the graph line 24, the graph line 26 has positive jerk from 0 seconds to 1 second in the first segment, no jerk from 1 second to 3 seconds in the second segment, negative jerk from 3 seconds to 4 seconds in the third segment, no jerk from 4 seconds to 6 seconds in the fourth segment, negative jerk from 6 seconds to 7 seconds in the fifth segment, no jerk from 7 seconds to 9 seconds in the sixth segment, and positive jerk from 9 seconds to 10 seconds in the seventh segment.

[0022] The present disclosure provides an improved technique with respect to what is shown in FIG. 2 regarding robot motion. This is to maintain the desired acceleration of the robot during the first to sixth segments described above in order to achieve a high robot cycle time during robot movement. Only in the seventh segment and the last segment, the acceleration of the robot 12 is reduced to the acceleration that reduces the tool jerk, thereby reducing the setting time required when the robot 12 stops before the tool 14 can start the cutting operation at the new location. Reducing the acceleration of the robot in the seventh segment reduces the amplitude of the positive jerk of the graph line 26 in the seventh segment, but extends the time required for the robot 12 to reach the destination. For example, instead of taking 1 second to move from the end of the sixth segment to the end of the seventh segment, it may take 2 seconds, which significantly reduces the tool jerk when the robot 12 stops at the end of the seventh segment. In the above-described embodiment, the seventh segment is only 1 second long and is the last deceleration section, so most of the robot's motion cycle is at the desired optimal speed, and thus the overall cycle speed is not significantly reduced.

[0023] When the robot 12 stops at the end of the seventh segment, it is the minimum or reduced tool jerk, and thus the settling time for stabilization is reduced. Therefore, the proposed or improved process of robot motion with a reduction in robot acceleration in the seventh segment has a cycle time faster than the existing technology that moves the robot as fast as possible, but waits to stabilize and settle the tool 14 at the end of the cycle. Further, the proposed process of robot motion maintains most of the desired robot speed during the movement cycle, and thus has a cycle time faster than the existing technology while reducing the speed of the robot 12 for the entire movement cycle. Also, the specialized programs previously required for optimal robot movement to achieve the desired robot speed and stabilization waiting time are reduced.

[0024] To execute the improved robot movement technology as described above, the control unit 18 separates the robot movement into a plurality of robot movement segments having different robot movement accelerations from the end of one tool operation to the start of the next tool operation. Here, one robot movement segment is the last robot movement segment immediately before the start of the next tool operation. The control unit 18 determines the optimal acceleration of the robot 12 for each robot movement segment that optimizes the cycle time of the robot movement in each robot movement segment. Here, the optimized cycle time is a predetermined maximum time. The control unit 18 reduces the optimal acceleration of the robot 12 during the last robot movement segment to less than the optimal acceleration so as to reduce the tool jerk when the robot reaches the start of the next tool operation.

[0025] The following graph shows an improved technology for the movement of the aforementioned robot. Figure 3 is a diagram showing the relationship between time on the horizontal axis and the magnitude of the robot speed on the vertical axis. Graph line 30 represents graph line 22 shown in Figure 2, but is different in the seventh segment. In particular, in the improved technology described in this specification, the speed of robot 12 is the same as the speed of robot 12 shown in Figure 2 except during the seventh segment. In this embodiment, graph line 30 is longer in the seventh segment. In particular, it takes more time for robot 12 to decelerate between point 34 and point 42. In the case of graph line 22, the seventh segment is between point 34 and point 39 and is represented by graph segment 32.

[0026] Figure 4 is a diagram showing the relationship between time on the horizontal axis and the magnitude of the robot acceleration on the vertical axis. Graph line 40 represents graph line 24 shown in Figure 2, but is different in the seventh segment. In particular, for the improved technology described in this specification, the acceleration of robot 12 is the same as the acceleration of robot 12 shown in Figure 2 except for the seventh segment. In this embodiment, the seventh segment of graph line 40 is longer. In particular, robot 12 is accelerating more between point 33 and point 43. In the case of graph line 24, the seventh segment is between point 33 and point 40 and is represented by graph segment 42.

[0027] Figure 5 is a diagram showing the relationship between time on the horizontal axis and the magnitude of the tool plus acceleration on the vertical axis. Graph line 50 represents graph line 26 shown in Figure 2, but is different in the seventh segment. In particular, for the improved technology described in this specification, the tool plus acceleration is the same as the tool plus acceleration shown in Figure 2 except for the seventh segment. In this embodiment, the seventh segment of graph line 50 is longer. In particular, it is longer between point 33 and point 44. In the case of graph line 26, the seventh segment is between point 35 and point 41 and is represented by graph segment 52.

[0028] Figure 6 shows the relationship between time on the horizontal axis and the magnitude of tool vibration on the vertical axis, and shows the stabilization of the robot for the prior art for robot movement and the improved technology for robot movement. Graph line 60 shows the robot stabilization for the prior art for robot movement, and graph line 62 shows the robot stabilization for the improved technology for robot movement. Line 64 represents the end of the seventh segment where the robot 12 stops and starts the next cutting operation. The movement of the robot for the improved technology ends later than the movement of the robot for the prior art, however, they are shown to occur in the same way for illustrative purposes only. Line 66 represents the line where the tool vibration is acceptable for a certain tool operation. Specifically, tool vibrations above line 66 are not allowed, and tool vibrations below line 66 are allowed. As is clear, the tool vibration becomes acceptable at time line 68 for the improved technology for robot movement, but is not allowed until time line 70 for the prior art for robot movement. Therefore, although the tool 14 reaches its destination faster for the prior art for robot movement than for the improved technology for robot movement, the time when the tool 14 becomes available to start the next cutting operation for the prior art for robot movement is longer than in the case of the improved technology for robot movement.

[0029] The foregoing description shows and describes merely exemplary embodiments of the present disclosure. Those skilled in the art will readily recognize from such discussion, as well as from the accompanying drawings and claims, that various changes, modifications, and variations can be made therein without departing from the spirit and scope of the disclosure as defined by the following claims.

Explanation of Reference Numerals

[0030] 10 Robot system 12 Robot 14 Tool 16 Part 18 Control unit

Claims

1. 1. A method for controlling movement of a robot holding a tool from the end of one tool operation to the start of a next tool operation, comprising: Separating the movement of the robot into a plurality of robot movement segments having different robot movement accelerations from the end of one tooling operation to the start of a next tooling operation, one of the plurality of robot movement segments being the last robot movement segment immediately prior to the start of the next tooling operation; Further, determining an optimal acceleration of the robot for each of the robot movement segments that optimizes a cycle time of the robot motion in each of the robot movement segments, the optimized cycle time being a predetermined maximum time; The method further comprises reducing the optimal acceleration of the robot in a final robot move segment below the optimal acceleration so as to reduce tool jerk when the robot reaches the start of a next tool motion.

2. 2. The method of claim 1, wherein the plurality of robot movement segments is seven segments and the final robot movement segment is a seventh robot movement segment.

3. The method of claim 1 , wherein the robotic tool is a laser cutting tool.

4. The method of claim 1 , wherein the final robot move segment is a final deceleration section of a combined robot move segment.

5. 1. A method for controlling movement of a robot holding a laser cutting tool from the end of one tool operation to the start of a next tool operation, comprising: Separating the movement of the robot into seven robot movement segments having different robot movement accelerations from the end of one tooling motion to the start of the next tooling motion; Further, determining an optimal acceleration of the robot for each of the robot movement segments that optimizes a cycle time of the robot motion in each of the robot movement segments, the optimized cycle time being a predetermined maximum time; The method further comprises reducing the optimal acceleration of the robot to less than optimal acceleration during a seventh robot movement segment to reduce tool jerk when the tool reaches the start of a next tool motion.

6. 6. The method of claim 5, wherein the seventh robot move segment is a final deceleration section of a combination of robot move segments.

7. 2. A system for controlling movement of a robot holding a tool from the end of one tool operation to the start of a next tool operation, comprising: A controller is provided. The controller separating the movement of the robot into a plurality of robot movement segments having different robot movement accelerations from the end of one tooling operation to the start of a next tooling operation, one of the plurality of robot movement segments being the last robot movement segment immediately prior to the start of the next tooling operation; and determining an optimal acceleration of the robot for each of the robot movement segments that optimizes a cycle time of the robot motion in each of the robot movement segments, the optimized cycle time being a predetermined maximum time; The system is further adapted to reduce the optimal acceleration of the robot in the last robot move segment below the optimal acceleration so as to reduce tool jerk when the robot reaches the start of a next tool motion.

8. 8. The system of claim 7, wherein the plurality of robot move segments is seven segments and the final robot move segment is a seventh robot move segment.

9. The system of claim 7 , wherein the tool is a laser cutting tool.

10. The system of claim 7 , wherein the final robot move segment is a final deceleration section of a combined robot move segment.

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