Torque Display of Axis for Diagnosis

Subject: Diagnosing a Servo Axis by using Torque Display
Controller: YRC1000
Product: Robot Axis and External Axis
Application: All (Spot Welding Example)
Robot: ALL
Security Level: Management or Safety

Summary: If trying to evaluate the force that is being applied by a servo axis it may be advantageous to evaluate the Torque level that is being applied by that axis.  The torque level is expressed as a % from 0-300% based on the current being drawn by the motor.  This is proportional and independent of the size of the motor, so all axes will read up to 300% even though they are different size motors.  The motors are grouped according to the Device with Robots grouped as 1-6 and External axes represented as Station#; S1, S2, etc.  The examples following are with a spot robot (R1) and a Servo Spot Gun (S1).
There are two useful ways to monitor the motor torque; by the Servo Monitor Display for numeric values or the Pendant Oscilloscope Function for graphic representation.

Servo Monitor Display: Select the ROBOT main menu > Servo Monitor menu.  This will display position and several other details according to selection.  The DISPLAY menu at the top of the pendant allows 2 items to be monitored side by side.  Item 1 can be specified as TORQUE SPEC and it will continually update with the torque value dynamically as the axes are moving.  Item 2 can be specified as MAX TORQUE and it will retain the peak torque value as the program runs.  The MAX value can be reset (in TEACH mode) by pressing the DATA menu in the upper right corner and pressing the CLEAR MAX TORQUE button.  In the case of a multi-axis system, press the PAGE key to advance display to show additional robot or station axes.

Example 1a: MAX TORQUE value of a Servo Gun (S1) clamping while robot was stationary.

Example 1b: ArcWorld 6200 with two AR1440 (R1,R2) and RM2 Positioner (S1-Main Sweep axis, S2,S3 Part Rotation Axes)

Pendant Oscilloscope Display: Select the ROBOT main menu > PENDANT OSCILLOSCOPE menu.  This will display the O-scope window and any channels will be noted on the right side with the units and start position noted on the left side.  The button CH is used to specify the channels desired to monitor.  By checking a channel you can specify the TARGET by pull down (SERVO for motor parameters) and the SIGNAL (TrqSpec for motor torque) and the Axis (will be the axis# in sequence).  For each channel selected a zero position needs to be defined (0 is the center X-axis) and a scale for the Y-axis divisions (pull down menu per monitored signal).  The TIMESCALE needs to be specified for the X-axis resolution.  Pressing START will begin the trace until STOP is pressed.  Trigger conditions can be specified to capture a signature. (For more information see Pendant Oscilloscope Function Manual 178665-1CD)

Example 2: Spot Weld Cycle with Servo Gun (S1; axis 7).  Channel 1 is axis speed and shows the gun opening/closing.  Channel 2 is torque and shows the Servo Gun motor coming to pressure (about neg 50% torque).  The signal to weld (green) comes ON when the gun motor is at pressure and lasts for about 0.3 sec.  The weld complete signal (magenta) from the spot power source comes ON and signals the Servo Gun to open.

Use the Channel Setting to specify the TrqSpec and Axis# to display on O-Scope.

Use the tabs to select the start position for each channel and the scale for the vertical axis.  Also specify the time scale for the horizontal axis divisions and trigger condition if desired.

Screen captures can be made of the display by holding the AUX key (lower left) and pressing the AREA key (upper right).  The .jpg image will be save to USB or CF memory in the pendant.  Data can be downloaded in .csv format to the memory device in the pendant also.