Prior Scientific OptiScan II ES107, Operating Instructions Manual

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Prior Scientific
5.11 Z Axis Encoder.
OptiScan II system can be equipped with either linear or rotary encoders for higher
positioning repeatability and accuracy, OptiScan II supports a Z axis encoder only.
A Z-probe or Z-encoder is an optical system that reflects light off a graduated scale through a
grating and onto photo sensors. These sensors generate electrical currents. The electrical
currents generated are used to determine distance and direction the stage has travelled.
Unlike rotary encoders which imply a distance travelled by measuring the rotation of the
motor, z probes measure actual focus travel by probing against the stage carrier for upright
microscopes or the nosepiece for inverted microscopes.
Z-probe Encoders benefit the OptiScan II user by providing:
•
The ability to provide closed loop "servo" control
•
Superior precision and finer resolution.
•
The ability to use an optional Digital Read Out (DRO)
The Z-probes used with OptiScan II controllers feature resolutions as little as 0.05 microns.
This superior performance is extremely critical in many Industrial and Bio-Science applications
such as the performance of time-lapse photography studies.
The OptiScan II Controller with the ‘E’ option enables encoder with RS485 differential
quadrature square wave outputs to be inputted to the Z axis. The controller will have a
round 12 pin connector on the back of the control box labelled, “Z encoder input”. Turn the
controller off and plug in the encoder or scale.
When an encoder is fitted and enabled (the default condition) the controller uses the
position measured by the encoder as the true position and not the number of pulses sent to
the stepper motor.
When the controller identifies an encoder fitted to the Z axis for the first power-up this
prompts a small motion to be initiated (two full steps of the motor). The controller will use
the number and sign of the counts from the encoder to establish the correct ratio between
encoder pulses and motor pulses.
Stepper moves will be faster than moves under encoder control due to the feedback,
checking, and adjusting required for the closed loop system.
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