September
1997, Issue 86
PC/104
Quarter:
Motion Control with PC/104
by
Chuck Raskin
PC/104
enables precise motion control to reach into the compact
capacity of the industrial application's closet. Chuck
guides the reader in what kinds of choices need to
be made when PC/104 and motion control come together.
Many
motion applications may be addressed by the simple on/off
I/O methods that everyone's familar with. Precise motion
control, on the other hand, requires high-speed control
of actuators (e.g., motors and hydraulics) via computers
or DSPs.
Typical
motion applications range from simple material handling
along one axis to robotics involving many axes of coordinated
motion, and CNCs. Modern controllers control position
with submicron accuracy and velocities to less than
0.01% tolerance.
When
motion has to be precisely coordinated, computer systems
generally provide the control. But, writing motion-control
algorithms that adequately handle real-time update requirements
within a specific application time frame isn't easy.
Off-the-shelf
motion-control products are designed to handle real-time
motion requirements and integrate simply into your applications.
Both servo and stepper motor controller devices are
available as add-in boards for several industrial standard
microcomputers--including PC/104.
The
flexibility gained from motion-control processors or
DSPs gives designers more powerful predefined algorithms
for designing board-level control. Hence, the art to
control is coordinating the needed motion with machine
timing requirements.
Obviously,
you don't want to reinvent motion software. But, software
written for a single computer environment isn't necessarily
the best answer.
A
single processor--be it an XT, '486, or even a DSP--is
usually tasked to the limit when calculating, processing,
and controlling more than four axes of linear servo
motion and two axes of circular algorithms in the time
required to maintain smooth motion and accomplish collateral
tasks.
True
single-level multitasking is achieved via single-board
multiple-axis motion-control cards in systems operating
under software control. They enable faster motion update
periods (under 256 µs per axis) for any number of axes,
solid machine control, and, with the proper I/O board,
increased system flexibility and modularity.
