For small to medium size robots, Jog Control Free Mode is very convenient for manually positioning the axes of a robot. In this mode, individual axes can be switched out of position control mode so that the axes are “free” to move and can be manually pushed to new positions that are to be taught.
For light weight axes that are not subject to gravity loading or excessive friction, the default settings of the controller permit the axes to be placed into Free Mode and manually positioned.
However, if axes are too large to safely permit free mode operation or if they are subject to a constant gravity load or if they have excessive static friction, there are a number of values within the Parameter Database that can be adjusted to accomodate the circumstances. These values are briefly described in the following table. For more detailed information on these parameters please see the Reference Document section.
| Parameter Database ID | Parameter Name | Description |
|---|---|---|
|
2823 |
Free mode inhibited axes mask |
This is a mask of bits that indicate axes that are not permitted to be placed into "Free" mode. For some mechanisms, allowing some or any axes to be taken out of position control mode with the brakes released may potentially result in damage to the robot or a hazardous situation. Turning on a bit in this mask will inhibit the corresponding axes from being placed into Free mode. The least significant bit in this mask corresponds to the first axis of the robot. |
|
2824 |
Free mode gravity comp motor mask |
This is a mask of bits that indicate motors that are to be dynamically gravity compensated when the corresponding axes is placed into "Free" mode. For motors that are subject to a large gravity force, if compensation of some sort is not applied, when an axis is "Free'd", it is possible that the axis may immediately collapse and damage the robot, other equipment or personnel. When a motor's bit is set in this mask word, the motor torque being generated in position control mode by the PID loop to hold the axis in position when Free Mode is enabled is assumed to be the constant torque required to counter the gravity force. The least significant bit in this mask corresponds to the first motor of the robot. NOTE:
|
|
2828 |
Free mode friction compensation, %rated |
For axes that have noticeable static friction, these parameters can enable compensation for the friction during jog control Free mode. When this feature is enabled and the operator presses on a Free'd axis and starts it moving, the system will generate a torque that assists in continuing to over-come the friction. So, once a Free'd axis begins to move, it takes less force to have it continue to move in the same direction. |
|
2829 |
Free mode friction deadband, mm/sec |
|
|
2830 |
Free mode friction rate of change, %/sec |
Rollover values are defined in joint coordinate units, typically degrees. Rollover values are normally set to be an even multiple of rotations, e.g. 360 deg, 720 deg, etc. Internally, the encoder counters are implemented as 32 bit counters. Therefore, encoder counters separately roll over every 4,294,967,296 counts. Joint rollover values when converted to encoder counts should always be less than half of the encoder rollover value. This is rarely a problem since a typical roll over value will be 360 deg times 2048 encoder counts per degree or 737,280 encoder counts.
The motion control system tests for a rollover condition at the following times;
Whenever a test detects that the absolute value of the joint position has exceeded the rollover value, the current joint position is decreased or increased by an even multiple of rollover values to bring it as close to zero as possible. Simultaneously with the adjustment of the joint value, an internal encoder offset is computed such that the actual motor position command is unchanged.