PAYLOAD program instruction
Syntax
PAYLOAD value, motor
Function
Adjust the feedforward compensation for a
specified motor by setting a percentage of the maximum payload assumed for
that motor.
Usage Considerations
This instruction affects the robot
currently selected with a SELECT program instruction.
A task does not have to be attached to the
robot to issue this instruction.
With Adept robots, this instruction is
supported only on motors 3 and 4 of the AdeptOne, the AdeptOne-XL, the
AdeptThree, the AdeptThree-XL, and the PackOne robots. The instruction is
useful primarily for tuning motor 4 performance as a function of end-effector
inertia. With AdeptMotion VME robots, the instruction defaults to no effect
and must be enabled with the SPEC utility.
For AdeptOne robots controlled by a SmartController with an
sEJI unit, the PAYLOAD instruction is implemented for motor 4. The PAYLOAD instruction has
no effect for other robots controlled by a SmartController.
Parameters
| value |
An optional real-valued expression
interpreted as a percentage of the maximum payload The range is 0% (no
payload) to 100% (maximum payload); a negative value restores the
default feedforward gain. If omitted, the value -1 is used, which is
interpreted as the default payload percentage. |
| motor |
An optional real-valued expression that
specifies to which motor this instruction applies. If the parameter is
omitted or zero, the payload percentage applies to all motors of the
selected robot. |
Details
The PAYLOAD instruction takes effect
immediately and is not synchronized with robot-motion segments.
If the PAYLOAD instruction is used to
indicate that a very large payload is on the robot motor when in fact a small
payload is on the robot motor, the motor can overshoot any time the commanded
acceleration is nonzero. The degree of overshoot depends upon the range
between minimum and maximum acceleration feedforward, the degree to which the
payload is in error, and the size of the acceleration and deceleration during
the motion being attempted. In particular, this is a concern for motor 4 of
the AdeptOne, the AdeptOne-XL, the AdeptThree, the AdeptThree-XL, and the
PackOne robots. Take care to ensure that the value used with the PAYLOAD
instruction correctly reflects the true payload.
On the AdeptOne, the AdeptOne-XL, the
AdeptThree, the AdeptThree-XL, the PackOne, and the Adept 550 robots:
You can use the PAYLOAD instruction to
adjust feedforward gains in a predetermined way, just as you can use the
GAIN.SET instruction to adjust feedback gains in a predetermined way. Because
GAIN.SET does not affect the feedforward, there is no conflict or direct
interaction between these two instructions. That is, the order of their
execution is unimportant.
The value parameter specifies a value of
the acceleration feedforward gain (inertia estimate) that is interpolated
between two factory preset values. These are the minimum no-load acceleration
feedforward gain and the maximum acceleration feedforward gain. A negative
value restores the default (nominal) feedforward gain. To calculate a
percentage for the
value parameter:
-
Open the SPEC utility. For details, see the section
Loading
and Executing Adept Utility Programs in the Instructions for Adept
Utility Programs Guide.
-
Select Edit robot specifications > Edit motor tuning parameters > Accel feedforward...
-
Divide the robot's maximum payload value
into the payload attached to the robot arm and then multiply by 100.
On AdeptMotion VME robots, this instruction
defaults to no effect. Using the SPEC utility program, you can enable it for a
particular AdeptMotion VME motor by setting the maximum and minimum
acceleration feedforward values for that motor to nonzero values (with the
maximum greater than the minimum). The PAYLOAD instruction assumes the use of
current-mode (torque-mode) amplifiers.
The benefit of the instruction depends upon
the mechanical design of the mechanism. Motors with low gear ratios and high
variations in payload benefit more. Motors with high gear ratios and low
variations in payload benefit less. The instruction is not useful with
velocity-mode amplifiers.
Related Keywords
ACCEL program instruction
ACCEL real-valued function
DURATION program instruction
DURATION real-valued function
SPEED monitor command
SPEED program instruction
SPEED real-valued function
