Tolerance based motion control system

• US 6,242,880 B1
• Filed: 09/01/1999
• Issued: 06/05/2001
• Est. Priority Date: 09/08/1998
• Status: Expired due to Term

• Current Assignee: Hurco Companies, Inc.
• Original Assignee: Cimplus, Inc.
• Inventors: Hong, Jaiwei
• Primary Examiner(s): Ip, Paul
• Application Number:
  US09/388,114
• Time in Patent Office: 643 Days
• Field of Search: 318/560-696, 318/39, 235/151.11, 235/152, 364/474-1-4, 364/171, 364/191
• US Class Current: 318/571
• CPC Class Codes: G05B 19/416 characterised by control of velocity, acceleration or deceleration G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/43203 Limitation of speed, permissible, allowable, maximum speed
• CPC Class Codes: G05B 2219/50179 Dynamic tolerance, limit values as function of speed, type of command

Abstract

The present invetion involves a tolerance based motion controller. The controller is capable of processing a group of tolerance constraints. The tolerance constraints specify where and when each tolerance constraint is to be applied, along with the information specifying the desired trajectory of motion. There are also a group of velocity constraints, specifying the maximum allowable velocity at each point along the desired trajectory. This information along with sensor feedback is used to modify the velocity along the actual trajectory of motion. This results in the time required traverse the trajectory being as short as possible. Also, the actual trajectory of motion should never exceed the permissible deviation from the desired trajectory, as specified by the tolerance constraints, with the velocity always being bounded by the specified velocity constraint.

Claims

1. A method of NC tolerance based motion control comprising the steps of:

specifying where and when what NC tolerance is requested by using NC tolerance commands;

obtaining the motion commands, including its desired trajectory and feedrate;

calculating feedrate limitations by mappings from desired trajectory of motion commands and NC tolerance requirement commands;

modifying the commanded feedrate by using the feedrate limitations;

executing the motion commands according to modified feedrate so that the requested NC tolerance may be satisfied.

2. An apparatus for NC tolerance based motion control for a machine tool using a part program and a desired error tolerance, comprising:

parsing means for parsing the part program into at least one segment, each segment including trajectory and error tolerance information;

calculating means for determining a modified feedrate value for each segment based on the associated trajectory and error tolerance information; and

executing means for operating the machine tool according to modified feedrate value so that the desired error tolerance may be satisfied.

3. A method of NC tolerance based motion control comprising the steps of:

specifying where and when what NC tolerance is requested by using NC tolerance commands;

obtaining the motion commands, including its desired trajectory and feedrate;

calculating feedrate limitations by mappings from desired trajectory of motion commands and NC tolerance requirement commands;

modifying the commanded feedrate by using the feedrate limitations;

executing the motion commands according to modified feedrate so that the requested NC tolerance may be satisfied.

4. An NC motion control system capable of processing NC tolerance requirements and motion commands with associated feedrates and modifying feedrates according to the desired trajectory of the motion command and NC tolerance commands so that the NC tolerance requirements may be satisfied, comprising:

motion command means to store a set of motion commands, including related feedrates;

tolerance command means to store a set of NC tolerance commands specifying where and when an NC tolerance is requested;

feedrate mappings means to calculate a set of feedrate limitation mappings that map the desired trajectory of motion commands and NC tolerance commands to the feedrate limitations that allows the motion command to be executed within the specified NC tolerance;

a processor capable of modifying the feedrate in the motion commands based on the feedrate limitation mappings, the motion command to be executed and the NC tolerance requirement for the said motion command, capable of reading position feedback signals, and capable of calculating motion signals according to the said motion command, the position feedback and the modified feedrate.

5. A method of tolerance based computer-controlled machine tool Numerical Controller (NC) comprising the steps of:

having the operator specify the intended NC tolerance level and generating NC tolerance commands therefrom;

obtaining a set of motion commands, the motion commands including desired trajectory and feedrate;

in a computer, calculating feedrate limitations by mappings from the desired trajectory of motion commands and the NC tolerance requirement commands;

modifying the set of feedrate commands based upon feedrate limitations; and

executing the motion commands, according to the set of modified feedrate commands, so that the NC tolerance may be reduced to the intended level;

thereby improving the control quality.

6. The method described in claim 5 wherein the NC tolerance commands are in the form of specialized G and M codes.