Load Acceleration/DecelerationLoads the maximum acceleration and/or deceleration value for an axis or vector space.
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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 or Vector Space is the axis or vector space to control. | ||||||||
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Inp Vect indicates the source of the 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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Acceleration is the acceleration (and/or deceleration) value in counts/s2 (servo axes) or steps/s2 (stepper axes). The default is 100000. | ||||||||
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Acceleration Type is the selector for loading acceleration, deceleration, or both acceleration and deceleration (default), as follows:
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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 Acceleration VI specifies the maximum rate of acceleration and/or deceleration for individual axes or vector spaces. When executed on a vector space, the value controls the vector acceleration (deceleration) along the vector move path.
You can use this VI to load separate limits for acceleration and deceleration or to set them both to the same value with one call. These parameters are double-buffered so you can load them on the fly without affecting the move in process, and they take effect on the next Start or Blend Motion call. After they are loaded, these parameters remain in effect for all subsequent motion profiles until re-loaded by this VI. You do not need to load acceleration before each move unless you want to change the acceleration and/or deceleration.
Acceleration defines how quickly the axis or axes come up to speed and is typically limited to avoid excessive stress on the motor, mechanical system, and/or load. A separate, slower deceleration is useful in applications where coming to a gentle stop is important.
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Note Use Load Move Constraints to load an acceleration of less than 1 count/s2. |
Remarks
This section includes information about how the behavior of this VI differs among the controllers that support it.
NI 73xx Controller Considerations
The following list includes considerations you must make when you are using this VI with a 73xx motion controller:
- Acceleration and deceleration values are converted to an internal 16.16 fixed-point format in units of counts/s2 before being used by the trajectory generator. You can calculate the minimum acceleration increment with the following formula:
minimum acceleration/deceleration = Amin × (
)2
where: Amin is 1/65,536 counts/sample2 or steps/sample2, Ts is the sample period in seconds per sample. - For a typical servo axis with 2,000 counts per revolution operating at the 250 ms update rate, calculate the minimum acceleration/deceleration increment using the following equation:
× 
= 0.122070 counts/s
- You can calculate the maximum acceleration/deceleration using the following equation:
maximum acceleration/deceleration = Amax × ()2
where: Amax is 32 counts/sample, Ts is the sample period in seconds per sample, and is constrained according to the following equations:
acceleration
256 × deceleration
deceleration 65536 × acceleration
- If you are doing onboard programming and are using Inp Vect to get the data this VI needs, remember that this VI reads the variables starting at the memory address pointed to by Inp Vect in the following order: Acceleration Type, Acceleration.
NI SoftMotion Controller Considerations
The following list includes considerations you must make when you are using this VI with the NI SoftMotion Controller:
- Use Load Counts/Steps per Revolution to set Counts(Steps)/Rev value to 1. Otherwise, NI-Motion returns an error.
- The range of acceleration/deceleration values is not limited by the fixed 16.16 calculation, and the NI SoftMotion Controller maintains full 64-bit precision.
- For the Inp Vect parameter, the NI SoftMotion Controller supports only the immediate return vector (0XFF).