8
Resolution - Stepper & Servo Motors
The resolution of a device is the smallest increment you can
command it to move. For example, sending the ASCII protocol
command
/move rel
1
instructs a device to move forward by
1 increment. The physical distance corresponding to this increment
depends on the type of motor that drives the device. For devices
driven by stepper motors, an increment is a microstep of the motor,
and the size of an increment is the device’s Microstep Size
specification. For servo devices, an increment is an encoder count,
and the size of an increment is the device’s Encoder Resolution
specification.
Microstepping
Stepper motors are designed for position control. In a motor
revolution, they have a number of equally-spaced full-step
positions. Most stepper motors in Zaber devices have 200 steps
per revolution.
Zaber’s drivers sub-divide each motor step into a number of
smaller increments called microsteps. By default, most devices use
a resolution of 64 microsteps per step (although this is adjustable),
so by default they can move to 12800 microstep positions for every
motor revolution.
Many devices use lead screws or gearing to move the actuators
or stages, so a motor revolution will move the device a certain
distance. That distance can be divided by the number of
microsteps per revolution to get the distance moved per microstep.
This is the Microstep Size. The Microstep Size will vary from device
to device; the value for your device is available on our website
under the ‘Series Specs’ tab for each product.
Encoder Counts
Unlike stepper motors, servo motors are designed with force
control in mind; they can be driven using position control, but the
resolution is very coarse. To achieve fine-resolution positioning,
Zaber’s servo devices feature a variety of digital and analog
position encoders for feedback. An encoder count is the smallest
movement of the encoder that will be registered by the controller.
Speed and Acceleration
While microsteps (for stepper motor devices) or encoder counts
(for direct drive devices) are the increments of position on Zaber
devices, there are conversion factors required to calculate the
increments of speed and acceleration.
Zaber Launcher and the programming libraries will handle this
conversion for you if you are using them. Otherwise, see the table
below for the conversion formula.
speed (in microsteps or encoder counts/second) = Data / 1.6384
acceleration (in microsteps or encoder counts/second²) = Data / 1638.4
