Tolerance based motion control system

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.

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.

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.

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.