Trajectory correlation and error detection method and apparatus

Apparatus for detecting the occurrence of a predetermined deviation between the desired positions of a programmed manipulator and respective actual positions during a repetitive work cycle, said programmed manipulator having a manipulator arm controllable in a plurality of axes, absolute position encoders for each of said axes to develop digital position signal representations, a digital memory having stored therein a plurality of command signals representing the desired position of said manipulator, and control apparatus for moving said manipulator arm to said desired position in response to said digital position signals from said absolute position encoders and said command signals stored in said digital memory, said detecting apparatus comprising:

• means for storing a series of digital signals from said absolute position encoders representing desired positions of said manipulator;
• means for recalling said stored signals during said work cycle;
• means for comparing said stored signals with the actual position signals from said absolute position encoders during said work cycle;
• and
• means responsive to said comparing means for determining when said manipulator is deviating from said stored desired position representations by a predetermined amount.

The method of detecting the occurrence of a predetermined deviation between the desired positions of a programmed manipulator and the respective actual positions thereof during a repetitive work cycle, said programmed manipulator having a manipulator arm controllable in a plurality of axes, absolute position encoders for each of said axes to develop digital position signal representations, a digital memory having stored therein a plurality of command signals representing the desired position of said manipulator, and control apparatus for moving said manipulator arm to said desired position in response to said digital position signals from said absolute position encoders and said command signals stored in said digital memory, the method comprising the steps of:

• storing a series of digital signals from said absolute position encoders representing the desired positions of said manipulator during a first work cycle at predetermined time intervals throughout said work cycle;
• recalling said stored signals during a work cycle subsequent to said first work cycle;
• comparing said stored signals with the actual position signals from said absolute position encoders at said predetermined time intervals during said subsequent work cycle;
• and
• determining when said actual manipulator position is deviating from each of said stored desired position representations by a predetermined amount.

In a programmable manipulator apparatus, the combination of:

• a manipulator arm movable in a plurality of axes;
• means for developing command signals representing desired positions of said arm in each of said axes;
• means for developing position signals representing the positions of said arm in a parallel data format in each of said axes;
• means responsive to said command signal means and said position signal means for moving said arm to the positions represented by said command signals;
• and
• means responsive to said position signal developing means and having stored therein a plurality of said position signals representing the positions of said arm for detecting a predetermined deviation between said stored position signals and said position signals from said position signal developing means;
• said detecting means further comprising means for storing a series of said position signals from said position signal developing means as said manipulator arm is moved through a plurality of desired positions defining a first operating cycle and for reading out said stored series of positions signals during operating cycles successive to said first cycle;
• means responsive to said storing and read out means and to said position signal developing means for comparing said stored position signals and said position signals from said position signal developing means at corresponding respective positions of said first and said successive operating cycles, said comparing means developing a difference signal related to the difference between said respective stored position signals and said signals from said position signal developing means,
• and means responsive to said difference signal for determining when said difference signal exceeds a predetermined limit,
• said storing and read out means comprising a memory stage operable in a record mode and a read out mode in a serial data format, means responsive to said position signal developing means for transforming said parallel data format to a serial data format, said parallel to serial transforming means providing said serial data format for recording into said memory stage, and means for transforming said data in a series format read out from said memory stage to a parallel data format for presentation to said comparing means.