04/03/00 Design News
Regional Technical Editor John Lewis
picks noteworthy power transmission products
Servos and steppers need brakes to stop
and hold dynamic loads when the power is shut off, and
the number of different types of brakes available is
growing. To wit, Ogura Industrial has just introduced
an electromagnetic spring-applied brake. This low-cost,
high-volume brake, called the MCLB, is a kind of little
brother to the popular MCNB Series. The design incorporates
a new high-temperature friction material that resists
glazing, producing more consistent braking torque and
the ability to handle higher cycle rates. Static torque
is 4.4 lb-inches. "Engineers want greater torque in
a smaller package, so the trick is to come up with a
design that achieves the best combination of performance
characteristics," says President Frank Fleming. The
brake design also features a low-inertia plastic hub,
which uses a spring to reduce hub chattering.
Ogura Industrial: Product Code 5061.
Free of couplings
An improperly aligned coupling between
a motor and leadscrew can wear bearings and reduce efficiency.
The PFC25-48D1 25-mm diameter linear actuator simplifies
such designs by eliminating the coupling. "By running
the lead screw shaft through the center of a step motor,"
says Kollmorgen's Director of Step Motor and Controls
Group Dave Beckstoffer, "this product simplifies designs,
and improves reliability." The rotor, composed of hub
and magnet assembly, spins inside a stationary yoke
that houses the coil winding. Each electronic pulse
that the motor receives initiates enough current flow
through the winding to provide sufficient torque to
move the rotor from one detent position to the next.
A dual-ball bearing design extends life and increases
the amount of side load the actuator can handle. "Engineers
also benefit because it allows them to change the lead
screw's pitch and alter the exerted force without changing
the package size," Beckstoffer adds. Designed for low-cost
and long-life in applications such as medical devices,
laboratory instrumentation, gas flow control, and printing
machines, the linear actuator is available in 0.48,
0.96, and 1.2 mm pitches.
Kollmorgen: Product Code 5044.
"When it comes to holding and stopping
brakes, the name of the game today is new mounting options,"
says Greg Cober, technical support and training manager,
Warner Electric/ DANA. "It used to be that design engineers
could only buy a flange-mounted failsafe brake. Now,
they are available in C-face mounting, which is one
area where we have seen a big expansion of our product
offerings." As a case in point, Warner recently introduced
a new series of permanent motor brakes for material
handling failsafe applications in two versions-one for
double-shaft motors and one for installation between
a C-face motor and drive device. Torque ratings range
from 6 to 56 lb-ft, depending on the specific size and
style. The brakes are also available with open and enclosed
Warner Electric: Product Code 5062.
S/R motor and drive
The Mavrik Motor division of Tridelta
Industries recently introduced a patented, two-phase
switched reluctance motor and drive package. The rotor
features a unique geometry, designed to improve torque
ripple, eliminate dead spots, reduce acoustic noise,
while at the same time simplifying sensor requirements
and control electronics. "The fact that electronic component
costs have come down, combined with development of microprocessor
capability and improvements in power electronics, has
made S/R motors more competitive today against other
technologies," says Gary Clark, director of marketing
for Mavrik. Though S/R motors have been around for 15
years, they are just now beginning to appear in volume
commercial applications. Design engineers favor them
for their unusual combination of high-reliability, high-speed
operation, and high-efficiency over a wide speed range.
Tridelta Industries: Product Code 5063.
RE series motors use rare-earth magnets
and graphite brushes to maximize the available torque
in a 40-mm (1.57-inch) diameter package. The patented
rhombic moving coil design provides for long life, low
electrical noise, fast acceleration, and high efficiency,
according to Maxon Precision Motors' Sales Manager Western
Div. Mike Rogen. "The most significant thing is the
torque to volume ratio. Having high torque in a small
package gives engineers more flexibility to move larger
loads." The 480-g (17 oz) motor is 71 mm (2.8 inches)
long and is rated at 150W. With three different windings
available, desired speeds can be achieved using available
voltage. Depending on the winding specified, RE series
motors achieve torque up to 200 milliNm (28 oz-inch),
and have mechanical time constants between 4 and 6 msec.
Maximum speed is 8,200 rpm, while the maximum efficiency
is 91%. Ambient temperature range is -20 to 100C (-4
to 212F). Matching gearheads and encoders are also available.
Applications include robotics, packaging equipment,
high-end industrial motorized hand tools, and medical
Maxon Precision Motors: Product Code
Simple systems designs
Pre-engineered components can simplify
system design and reduce cost. "Using our belt, patented
timing pulley, and tension system with off-the-shelf
components from other vendors shows how simple it is
to build a system using strictly commercial components,"
says Tim Potrikus, sales and marketing manager at Belt
Technologies. "Our products integrate easily with just
about any popular motion control package that's out
there." Non-stretch stainless-steel belts are known
for their high strength-to-weight ratio, durability,
and precise positioning. They also run without lubrication
of any kind, offer unlimited travel lengths, and efficiently
dissipate heat and discharge static. "Depending on the
alloy chosen," explains Potrikus, "these belts hold
up in caustic environments at very low temperatures
or up to 1,500F-places where other motion control devices
might not work."
Belt Technologies Inc.: Product Code