Load Torque OffsetLoads primary and secondary DAC torque offsets for an axis.
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Secondary Offset (0)
is the secondary DAC torque (or velocity) offset. The offset range is –32,768 to +32,767 (–10 V to +10 V) with a default value of 0 (0 V).
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Primary Offset (0) is the primary DAC torque (or velocity) offset. The offset range is –32,768 to +32,767 (–10 V to +10 V) with a default value of 0 (0 V). | ||||||
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Board ID is a unique number assigned by Measurement & Automation Explorer (MAX) used to send and receive commands and data to or from a specific NI motion controller. | ||||||
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Axis is the axis to control. | ||||||
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Inp Vect contains the primary and secondary parameters that are the source of data for this VI.
Available input vectors include immediate (0xFF), variable (0x01 through 0x78), or indirect variable (0x81 through 0xF8). Refer to Input and Return Vectors for more detailed information. |
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error in (no error) describes error conditions that occur before this VI runs. The default input of this cluster is no error. If an error already occurred, this VI returns the value of error in in error out. The VI runs normally only if no incoming error exists. Otherwise, the VI passes the error in value to error out. The error in cluster contains the following parameters:
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Bd ID Out is provided for flow control. You can string together NI-Motion VIs by wiring the Bd ID Out terminal of one VI to the Board ID terminal of the next VI. | ||||||
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Resource Output is the Axis, Vector Space, ADC, or Encoder you wired into the VI. Use Resource Output to pass the resource to another VI and/or to display information about the device. | ||||||
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error out contains error information. If error in indicates an error, error out contains the same error information. Otherwise, it describes the error status that this VI produces.
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Using This VI
The Load Torque Offset VI loads offset values for the DACs mapped to the selected servo axis. This VI has no effect on stepper axes or independent DAC outputs that are not mapped to an axis. When a DAC is connected to a velocity block servo amplifier, the torque offset functions as a velocity offset.
A torque (or velocity) offset shifts the DAC output(s) by the programmed offset value without requiring any action from the PID loop. In a servo system, this can be used to overcome amplifier input offsets, system imbalances, or the effects of outside forces such as gravity. Different torque offsets can be loaded for the primary and secondary DAC.
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Note When an Axis is killed, its DAC outputs are zeroed regardless of the torque offset loaded. |
DAC offsets can be used in conjunction with DAC range limits to interface to servo amplifiers with unipolar input ranges (for example, 0 to 5 V or 0 to 10 V).
Example
Calling the Load Torque Offset VI with Primary Offset = 4,096 and Secondary Offset = 0 shifts the output ranges of the primary DAC mapped to the axis as shown in the following figure:
The result of this VI call is to limit the primary DAC to a range of –8.75 V to +10 V with an offset or null value of +1.25 V. This is because even when the PID loop is commanding full negative torque, the torque offset is added and the resulting output is –8.75 V. In the positive direction, the DAC cannot go above +10 V no matter what the offset is.
The VI call leaves the secondary DAC offset at its default value of zero (0). This example assumes the full torque range is available and not limited by the Load Torque Limit VI.
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Note The offset value must be within the range limits set by the Load Torque Limit VI. |