User`s guide

This factor can be determined either directly from the details of the mechanical coupling of
the encoder to the belt or experimentally by reading the encoder as the belt is moved. The
Adept belt calibration program supports either method of determining the encoder scaling
factor.
If the encoder counter decreases as the belt moves in its normal direction of travel, the
scaling factor will have a negative value.
The Encoder Offset
The last encoder value needed for proper operation of the conveyor-tracking system is the
belt encoder offset. The belt encoder offset is used by V+ to establish the instantaneous
location of the belt reference frame relative to its nominal location.
In particular, if the belt offset is set equal to the current belt encoder reading, the
instantaneous belt transformation will be equal to the nominal transformation. The belt
encoder offset can be used, in effect, to zero the encoder reading, or to set it to a particular
value whenever necessary. Unlike the encoder scaling factor, which is constant for any given
conveyor/encoder setup, the value of the belt encoder offset is variable and will usually be
changed often.
Normally, the instantaneous location of the reference frame will be established using
external input from a sensory device such as a photocell or the AdeptVision system. For
example, the VFEATURE function provided by AdeptVision returns as one of its computed
values the belt encoder offset that must be set in order to grasp an object identified by the
vision system. The DEVICE real-valued function also returns latched or unlatched encoder
values for use with SETBELT.
The encoder offset is set with the SETBELT program instruction, described in Belt Variable
Definitions on page 317.
The Belt Window
The belt window controls the region of the belt in which the robot is to work. The figure
Conveyor Terms illustrates the terms used here. A window is a segment of the belt bounded
by two planes that are perpendicular to the direction of travel of the belt. When defining the
window, ensure that the robot can reach all conveyor locations within the belt window. This
is especially important for revolute (i.e., non-Cartesian) robots.
NOTE: The window has limits only in the direction along the belt.
Within V+, a belt window is defined by two transformations with a WINDOW program
instruction. The window boundaries are computed by V+ as planes that are perpendicular to
the direction of travel of the belt and that pass through the positions defined by the
transformations.
If the robot attempts to move to a belt-relative location that has not yet come within the
window (is upstream of the window), the robot can be instructed either to pause until it can
accomplish the motion or immediately generate a program error. If a destination moves out
Basic Programming Concepts
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