Resonance detection and resolution

• US 6,028,410 A
• Filed: 01/11/1999
• Issued: 02/22/2000
• Est. Priority Date: 01/11/1999
• Status: Expired due to Term

• Current Assignee: Stratasys Incorporated
• Original Assignee: Stratasys Incorporated
• Inventors: Rapoport, Edward, Comb, James W., Leavitt, Paul J.
• Primary Examiner(s): Ip, Paul
• Application Number:
  US09/228,312
• Time in Patent Office: 407 Days
• Field of Search: 318/560-696, 395/80-96, 364/167.01, 364/174, 364/148, 364/176, 364/152, 364/153, 382/243, 382/236, 382/232, 382/235, 382/238
• US Class Current: 318/568.15
• CPC Class Codes: B25J 9/1664 characterised by motion, path, trajectory planning
• CPC Class Codes: B33Y 50/02 for controlling or regulating additive manufacturing processes
• CPC Class Codes: G05B 19/404 characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia G05B19/19, G05B19/41 take precedence
• CPC Class Codes: G05B 2219/39214 Compensate tracking error by using model, polynomial network
• CPC Class Codes: G05B 2219/40057 Contour tracking, edge following
• CPC Class Codes: G05B 2219/43131 Adapt speed as function of lag, follow up error

Abstract

The present invention provides a method for controlling following error in a robotic system that moves a tool at a velocity along a path defined by an inputted set of vertices. The following error is controlled to be less than a tolerable error allowance. First, a subset of resonant vertices is identified from the inputted set of vertices. Each of the resonant vertices has a neighboring vertex for which a following error that results when the tool negotiates both the vertex and its neighboring vertex at an assigned vertex velocity might exceed the tolerable error allowance. Second, each vertex in the subset of resonant vertices is assigned a reduced vertex velocity. The reduced vertex velocity is selected so that the following error that results when the tool negotiates both the vertex and its neighboring vertex at the reduced velocities is less than the tolerable error allowance.

Claims

1. A method for controlling a following error in a robotic system that moves a tool at a velocity along a predefined path defined by an inputted set of vertices, each of the vertices in the inputted set of vertices having an assigned vertex velocity, the following error being controlled to be less than a tolerable error allowance, the method comprising:

identifying a subset of resonant vertices from the inputted set of vertices, the resonant vertices each having a neighboring vertex for which a following error that results when the tool negotiates both the vertex and its neighboring vertex at the assigned vertex velocities might exceed the tolerable error allowance; and

assigning a reduced vertex velocity to each vertex in the subset of resonant vertices, the reduced vertex velocity being selected so that the following error that results when the tool negotiates both the vertex and its neighboring vertex at the reduced vertex velocities is less than the tolerable error allowance.

2. The method of claim 1 and further comprising:

identifying pairs of resonant vertices from the subset of resonant vertices for which a tool travel time between the pair of resonant vertices is less than a resonance window period when the velocity of the tool is controlled according to a nonresonant velocity profile; and

reclassifying as resonant vertices those vertices that lie between the identified pairs of resonant vertices.

3. The method of claim 2 and further comprising:

controlling the velocity of the tool according to a resonant velocity profile when traveling between the identified pairs of resonant vertices with a resonant velocity profile.

4. The method of claim 1 wherein the reduced vertex velocities are reduced to a value not in excess of a low-limit velocity.

5. The method of claim 1 wherein the reduced vertex velocities are reduced to equal a low-limit velocity.

6. A method for controlling a following error in a robotic system that moves a tool at a velocity along a predefined path defined by an inputted set of vertices, the following error being controlled to be less than a tolerable error allowance, the method comprising:

assigning a vertex velocity to each vertex, the vertex velocity being selected so that the resultant following error when the tool negotiates the vertex at its assigned vertex velocity is less than the tolerable error allowance;

identifying a subset of resonant vertices from the inputted set of vertices, the resonant vertices each having a neighboring vertex for which the resultant following error when the tool negotiates both the vertex and its neighboring vertex at the assigned vertex velocities might exceed the tolerable error allowance; and

assigning a reduced vertex velocity to each vertex in the subset of resonant vertices, the reduced vertex velocity being selected so that the resultant following error when the tool negotiates both the vertex and its neighboring vertex at the reduced vertex velocities is less than the tolerable error allowance.

7. The method of claim 6 and further comprising:

identifying pairs of resonant vertices from the subset of resonant vertices for which a tool travel time between the pair of resonant vertices is less than a resonance window period when the velocity of the tool is controlled according to a nonresonant velocity profile; and

reclassifying as resonant vertices those vertices that lie between the identified pairs of resonant vertices.

8. The method of claim 7 and further comprising:

controlling the velocity of the tool according to a resonant velocity profile when traveling between the identified pairs of resonant vertices with a resonant velocity profile.

9. The method of claim 6 wherein the reduced vertex velocities are reduced to a value not in excess of a low-limit velocity.

10. The method of claim 6 wherein the reduced vertex velocities are reduced to equal a low-limit velocity.

11. A method for detecting and resolving resonance in a robotic system that moves a tool at a velocity along a predefined path defined by an inputted set of vertices, each of the vertices having a vertex velocity associated with it, the method comprising:

identifying a subset of resonant vertices from the inputted set of vertices; and

reducing the vertex velocities that both exceed a predefined low-limit velocity and are associated with identified resonant vertices.

12. The method of claim 11 and further comprising:

identifying pairs of resonant vertices from the subset of resonant vertices for which a tool travel time between the pair of resonant vertices is less than a resonance window period when the velocity of the tool is controlled according to a nonresonant velocity profile; and

reclassifying as resonant vertices those vertices that lie between the identified pairs of resonant vertices.

13. The method of claim 12 and further comprising:

controlling the velocity of the tool according to a resonant velocity profile when traveling between the identified pairs of resonant vertices with a resonant velocity profile.

14. The method of claim 11 wherein the reduced vertex velocities are reduced to a value not in excess of the low-limit velocity.

15. The method of claim 11 wherein the reduced vertex velocities are reduced to equal the low-limit velocity.

16. A method for detecting and resolving resonance in a robotic system that moves a tool a velocity along a predefined path defined by an inputted set of vertices, each of the vertices having a vertex velocity associated with it, the method comprising:

identifying a subset of suspect vertices from the inputted set of vertices;

identifying a subset of resonant vertices from the subset of suspect vertices;

adjusting vertex velocities that both exceed the low-limit velocity and are associated with identified resonant vertices;

identifying pairs of resonant vertices from the subset of resonant vertices for which a tool travel time between the pair of resonant vertices is less than a resonance window period when the velocity of the tool is controlled according to a nonresonant velocity profile;

reclassifying as resonant vertices those vertices in the inputted set of vertices that lie between the identified pairs of resonant vertices; and

controlling movement of the tool according to a resonant velocity profile when traveling between the identified pairs of resonant vertices.

17. The method of claim 16 wherein the adjusted vertex velocities are adjusted to equal a value not in excess of the low-limit velocity.

18. The method of claim 16 wherein the adjusted vertex velocities are adjusted to equal the low-limit velocity.

19. A method for controlling movement of a tool in a robotic system that moves the tool at a velocity along a path defined by an inputted set of vertices, the method comprising:

assigning a vertex velocity for each of the inputted vertices;

identifying a subset of resonant vertices from the inputted set of vertices;

reducing the vertex velocity associated with each identified resonant vertex having an associated vertex velocity that exceeds a predefined low-limit velocity; and

controlling movement of the tool based upon the reduced vertex velocities associated with each vertex in the inputted set of vertices.

20. The method of claim 19 wherein the step of calculating a vertex velocity for each of the inputted vertices comprises:

calculating a dimensional vertex velocity for each axis in the robotic system;

setting the vertex velocity associated with each vertex to the smallest of the dimensional vertex velocities associated with that vertex; and

reducing vertex velocities in excess of a steady-state velocity to equal the steady-state velocity.

21. The method of claim 19 wherein the step of identifying a subset of resonant vertices from the inputted set of vertices comprises:

identifying a subset of suspect vertices from the inputted set of vertices;

identifying an initial subset of resonant vertices from the subset of suspect vertices;

identifying pairs of resonant vertices from the initial subset of resonant vertices for which a tool travel time between the pair of resonant vertices is less than a resonance window period when the velocity of the tool is controlled according to a nonresonant velocity profile; and

reclassifying as resonant vertices those vertices in the inputted set of vertices that lie between the identified pairs of resonant vertices.

22. The method of claim 19 wherein the reduced vertex velocities are reduced to equal a value less than the low-limit velocity.

23. The method of claim 19 wherein the reduced vertex velocities are reduced to equal the low-limit velocity.