Page 731 - Mechatronics with Experiments

CHAPTER 10

PROGRAMMABLE MOTION

CONTROL SYSTEMS

10.1 INTRODUCTION

Programmable motion control systems (PMCS) are used in all mechanical systems that
involve computer controlled motion. A robotic manipulator, an assembly machine, a CNC
machine, XYZ table, and construction equipment tool control systems are all examples of
applications of PMCS. As the name indicates, PMCS are motion mechanisms where the
motion is controlled by a digital computer, and hence are programmable. PMCS are good
examples of mechatronic systems in that they involve a mechanical motion system, various
actuators and sensors, and computer control. Figure 10.1 shows the typical components
of an electric motor based programmable motion system, that is a motor with position
sensor, amplifier and power supply (drive), and controller. The figure shows different types
of rotary motors and drives (brushless and brush-type DC, AC induction) as well as linear
motors.
In the past, coordinated motion control in automated machines was achieved by
mechanically connecting various machine components with linkages, line shafts, and gears.
Once the master line shaft is driven by a constant speed motor or engine, the rest of the
motion axes derive their motion from it based on the mechanical linkage relation. This was
what is called “hard automation.” The availability of low cost microprocessors and digital
signal processors (DSP) as well as their high reliability has made it possible to control
motion and coordinate various axes under computer control. The coordination between
axes is not fixed by mechanical linkages, but coded in software. Hence, the coordination
logic can be changed on the fly in software. The same machine can be used to perform with
different coordination relations to produce different parts by simply changing software. In
mechanically coordinated machines this may require a change of gears, linkages which
may require very long setup times. Some of the complicated coordination functions may
not even be feasible to achieve by mechanical coordination while they can be easily coded
in software. The “programmable” aspect of motion control comes from the fact that the
control logic is programmed. Therefore, it is a “soft automation” or “flexible automation.”
The single most significant advantage of “soft automation” over “hard automation” is the
significantly reduced setup times for product changeovers. Figure 10.2 shows an example
of a printing machine with both old mechanical automation and programmable automation
versions. In the mechanical version, each station is coordinated with respect to the master
shaft through mechanical gears. When a different product is required, the gear reducer
ratios are mechanically changed. Therefore, for different products, different gear reducers
have to be kept in the inventory. In addition, physically changing the gear reducers is labor
intensive and time consuming. In the electronically coordinated version of the machine, the

Mechatronics with Experiments, Second Edition. Sabri Cetinkunt.
© 2015 John Wiley & Sons, Ltd. Published 2015 by John Wiley & Sons, Ltd.
Companion Website: www.wiley.com/go/cetinkunt/mechatronics

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