Cognex MVS-8000 Series, Руководство по оборудованию

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MVS-8600 Hardware Manual 79
Using Encoders with
Line Scan Cameras
An encoder is an electromechanical transducer that converts rotary or linear motion into
electrical signals. Encoders are used to determine speed, velocity, distance, position,
or direction. Examples of encoder types vary widely, and include equipment as different
as an airplane’s altimeter or a computer’s trackball.
When used with a line scan camera, an encoder provides a mechanism to keep track of
the position and direction of the scene under the camera lens. Line scan cameras
capture one row of pixels at a time, and build up an image by combining hundreds of
rows into an image.
Encoders and the MVS-8600 Series
MVS-8600 series frame grabbers use encoder inputs to:
• Monitor the rate of motion of the scene being imaged by a line scan camera
• Detect a direction change, or a halt in the scene motion
The MVS-8600 cannot acquire an image from a line scan camera without an encoder
input. It is the encoder input that the frame grabber uses to calculate the rate at which
lines are acquired.
CVL and VisionPro software provide a software-based test encoder that can be used to
simulate encoder input for testing and setup, in lieu of a hardware encoder.
In CVL, when ccEncoderProp::useTestEncoder() is enabled, the hardware acquires
lines as fast as possible without using a hardware encoder input. The
ccEncoderProp::stepsPerLine() setting is ignored. To introduce a delay between
acquisitions of successive lines, you can specify a positive trigger delay value. See the
ccTriggerFilterProp reference page for information about how to do this.
In VisionPro, the ICogAcqLineScan.TestEncoderEnabled and
ICogAcqTriggerFilter.TriggerDelay properties provide the same capability.
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