Checking the Accuracy of the Force Sensor

Overview

This section describes a method to check if the Force Sensor is working properly.

Accuracy abnormality may occur if the Force Sensor is damaged by being hit or applied the load which exceeds the rated load. Accuracy abnormality can be checked by comparing the data acquired before use of the Force Sensor (initial data) and the data acquired after the accuracy error was found (comparison data). If abnormality is found while using the Force Sensor, follow the steps below to check the accuracy of the Force Sensor. When performing the accuracy check, be sure to obtain the initial data before using the Force Sensor.

Accuracy guaranty of the Force Sensor is ±5%. We recommend to replace the Force Sensor if the guaranty value is exceeded when checking the accuracy. However, depending on the applications, some of them are still available if the guaranty value is exceeded. Replace the Force Sensor depending on the usage.

Acquisition of the Initial Data

This section describes how to obtain the initial data.

The initial data can be obtained by sample programs on the following pages. The programs differ between 6-axis robots and SCARA robots. Choose the program according to your Manipulator. This data is used when checking the accuracy of the Force Sensor. Be sure to save the acquired data.

CAUTION

Change the initial position and motion of the Manipulator according to your usage environment, and make sure that the robot, end effector, cables, and peripherals do not interfere with each other.

Function ForceSensorLog6Axis       ' Sample program for 6-axis robots
  FSet FM1.Label, "ForceLog"       ' Specifies a label used by the filename.
  Tool 0                           ' Specifies Tool 0
  FSet FM1.CoordinateSystem, FCS0  ' Specifies the Tool coordinate system for the Force coordinate system
  FSet FM1.ForceSensor, 1          ' Specifies the Force Sensor number
  FSet FM1.LPF_Enabled, False, False, False, False, False, False, False, False
    ' Disable a low pass filter
  MP 0                             ' Stops the gravity compensation

  Motor On                         ' Motor on
  Go AglToPls(0, 0, 0, 0, 0, 0)    ' Moves to the initial position

  FSet FS1.Reset                   ' Reset the Force Sensor
  FSet FM1.RecordStart, 60, 0.1    ' Starts logging the Force Sensor values
  ' -----------------Operation part------------------
  Motor On                         ' Motor on
  Wait 2
  Go AglToPls (0, 0, 0, 0, 90, 0)
  Wait 2
  Go AglToPls (0, 0, 0, -90, 90, 0)
  Wait 2
  Go AglToPls (0, 0, 0, -90, -90, 0)
  Wait 2
  Go AglToPls (0, 0, 0, 0, -90, 0)
  Wait 2
  Go AglToPls (0, 0, 0, 0, 0, 0)
  Wait 2
  ' ------------------------------------------
  FSet FM1.RecordEnd               ' Finishes logging the Force Sensor values
Fend

Function ForceSensorLogSCARA       ' Sample program for SCARA robots
  FSet FM1.Label, "ForceLog"       ' Specifies a label used by the filename.
  Tool 0                           ' Specifies Tool 0
  FSet FM1.CoordinateSystem, FCS0  ' Specifies the Tool coordinate system for the Force coordinate system
  FSet FM1.ForceSensor, 1          ' Specifies the Force Sensor number
  FSet FM1.LPF_Enabled, False, False, False, False, False, False, False, False
    ' Disable a low pass filter
  MP 0                             ' Stops the gravity compensation

  Motor On                         ' Motor on
  Go AglToPls(0, 0, 0, 0)          ' Moves to the initial position

  FSet FS1.Reset                   ' Reset the Force Sensor
  FSet FM1.RecordStart, 60, 0.1    ' Starts logging the Force Sensor values
  ' -----------------Operation part------------------
  Motor On                         ' Motor on
  ' Power High                     ' High power mode
  ' Accel 50, 50                   ' Acceleration setting
  ' Speed 50                       ' Speed setting
  Wait 2
  Go AglToPls (0, 90, 0, 0)
  Wait 2
  Go AglToPls (0, 90, 0, -90)
  Wait 2
  Go AglToPls (0, 0, 0, -90)
  Wait 2
  Go AglToPls (0, 0, -50, -90)
  Wait 2
  Go AglToPls (0, 0, 0, -90)
  Wait 2
  Go AglToPls (0, 0, 0, 0)
  Wait 2
  ' ------------------------------------------
  FSet FM1.RecordEnd               ' Finishes logging the Force Sensor values
Fend

Description

  1. Specify a label. The date and the time of execution are added to the label to form the filename.
    Set arbitrary file location and name for the file.
  2. Specify Tool 0, and specify the Tool coordinate system for the Force coordinate system.
    A user-configured tool can be used. Also, while FCS0 is a Force coordinate system which matches the default Tool coordinate system, user-defined Force coordinate objects can be used .
  3. Specify the sensor number.
    Specify the sensor number of the Force Sensor that the initial data will be acquired.
  4. Disable a low pass filter and stop the gravity compensation.
  5. Turn ON the motor, and move the robot to the initial position.
    In the sample program, the robot moves to the home position. The robot also can be moved to the user-specified position.
  6. Reset the Force Sensor.
  7. Start recording the Force Sensor values. The values will be recorded for 60 seconds with 0.1 second intervals.
  8. Move the robot to change the Force Sensor's orientation.
    In the sample program for 6-axis robots, Joints #4 and #5 are moved from the home position to change posture of the Force Sensor. User-specified motion is also available. However, that motion should cause the sensor's angle to change from the initial position by 10° or more in each direction.
    In the sample program for SCARA robots, Joints #2, #3, and #4 are moved from the home position to apply an inertia force to the Force Sensor. In order to record the inertia force, the measurement interval for the sensor values is shorter compared to the sample program for 6-axis robots. User-specified motion is also available. Note, however, that 1[N] or more force should be applied in each direction of the sensor from the initial position. In the sample program, the speed and acceleration settings are commented out. Confirm that the motion has no problem and enable the commands.
  9. Stop recording the Force Sensor values.

Key Point

Acquired Force Sensor values are affected by the following settings.

  • Base coordinate setting (Base)
  • Local coordinate setting (Local)
  • Tool setting (Tool, TLSet)
  • Flange offset setting (F_FlangeOffset)
  • Force Coordinate Object (FCS#)

Save the above setting values so that these can be reproduced when acquiring the comparison data.

Key Point

The Force Sensor values are affected by physical installation conditions, such as the tilt of the robot, and shapes and weight of the sensor flange and end effectors. Therefore, be sure to acquire the initial data again when the usage environment changes.

Acquisition of the Comparison Data and Comparison with the Initial Data

When the accuracy abnormality of the Force Sensor is found, obtain the comparison data and compare it with the initial data.

The comparison data should be obtained with the same procedure and conditions as the initial data acquisition. Note that the conditions include physical installation environment, setting values, and motion in data acquisition.

If a large difference between the outputs of the Force Sensor is found by comparing the initial data and the comparison data acquired with the same condition as the initial data, the Force Sensor cannot be used.

Accuracy abnormality may occur if the Force Sensor is damaged by being hit or applied the load which exceeds the rated load. Use the Force Sensor within the range of specifications. For details on the specifications, refer to the following section.

Hardware Specification

← Force Sensor Correction →

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