Electrical Drives
Selecting Electrical Drives
The days of matching catalog motors with available power supplies and
controllers may be over. The old way of handling motion control was to choose
off-the-shelf devices with ratings usually exceeding actual application requirements.
This was especially true for controllers available in three or four models each
designed to accommodate a range of motor sizes. The result was often an
overrated (in current, voltage, or both) and expensive controller driving a
larger-than-needed motor.
Overspecified systems of this nature may be all right in small quantities.
But in volume OEM production where price is an important consideration,
a better matching between components becomes critical.
In addition, the performance demands made on today's motion-control systems
frequently eliminate off-the-shelf products from contention. These demands
concern high acceleration and deceleration rates, tight speed accuracies,
and fine adjustment increments that are difficult to reach using collections of
standard products.
Another approach is increasingly being used to meet such requirements.
Rather than make do with standard parts, it is often better to design the motor
and controller together as an optimized system. This technique involves constructing
a motor from a few building block components and matching it with a power supply
and controller that together provide the needed performance at a minimum cost.
Successful examples of this approach can be found in the retrofitting of
electronic controls to mechanical production or manufacturing equipment
in machine tools; filament-winding, packaging and labeling machinery; avionics
controls and actuators; industrial sewing machines; and optical recording equipment.
A number of problems can make standard motion-control products suboptimum.
One is that off-the-shelf motors generally come with a set performance and
fixed dimensions. Shaft diameters and lengths, motor diameters, and supply voltage
requirements are generally invariable.
It is often difficult to get motor manufacturers to make even slight changes in
these specifications. For example, ordering a standard motor with a special rear
shaft extension may result in a sharp jump in both price and lead time, assuming
the vendor is willing to make the modification at all.
|
