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 housings.
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 equipment.
Maxon Precision Motors: Product Code 5045.
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 5046.