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HA0276T Rev Bk Jan 2017
Chapter 7
C.1.2
Positive and Negative Moves
Positive
and
negative
are used to describe the direction of a move. A positive move
means a move from a smaller absolute position to a larger one, a negative move
means the opposite.
In the case of a linear actuator, a positive move takes the platform of the stage further
away from the motor.
In a rotational stage, a positive move turns the platform clockwise when viewed from
above.
C.1.3
Velocity Profiles
To prevent the motor from stalling, it must be ramped up gradually to its maximum
velocity. Certain limits to velocity and acceleration result from the torque and speed
limits of the motor, and the inertia and friction of the parts it drives.
The motion employed is described by a trapezoidal velocity profile, reflecting the
shape of the velocity
vs.
time graph (see Fig. C.2.), thereby driving the stage to its
destination as quickly as possible, without causing it to stall or lose steps.
The stage is ramped at acceleration ‘
a’
to a maximum velocity ‘
v’
. As the destination
is approached, the stage is decelerated at ‘
a’
so that the final position is approached
slowly in a controlled manner
.
Fig. C.2 Graph of a trapezoidal velocity profile
C.2
Positioning a Stage
C.2.1
General
Whenever a command is received to move a stage, the movement is specified in
motion units, (e.g. millimetres). This motion unit value is converted to microsteps
before it is sent to the stage. If operating the unit by the front panel (local mode) this
conversion is performed internally by the controller. If operating via a PC (remote
mode) then the conversion is performed by the Kinesis software.
Each motor in the system has an associated electronic counter in the controller, which
keeps a record of the net number of microsteps moved. If a request is received to
report the position, the value of this counter is converted back into motion units.
velocity
maximum
velocity (v)
time
acceleration (slope) a
Summary of Contents for Kinesis MLJ050
Page 1: ...MLJ050 Motorized Lab Jack Kinesis User Guide Original Instructions ...
Page 42: ...42 D 3 CE Certificate ...
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