Machine Design

Scanning for Ideas: Magnetic brake’s microcontroller eliminates cogging and nonlinearity

Magnetic brakes have suffered from hysteresis, cogging, and low-power output for over 30 years. And they have lacked linearity, so users had to more than double the input signal to double the output force of the brake. To solve these problems, engineers at Magnetic Brake Systems, Camarillo, Calif., designed a new type of magnetic brake. It uses a microcontroller to ensure output torque is linear with input signals, regardless of whether the control signal is increasing or decreasing.

The same microcontroller eliminates cogging which, on some magnetic brakes, can be as high as 25% of the brake’s maximum torque. The microcontroller ensures that within 500 msec after the input signal goes to zero, cogging disappears — and with no rotation of the brake drag ring.

The brakes can exert constant tension instead of constant torque, which is useful for unwinding wire or films from variable-diameter feed rolls. To do this, the microcontroller monitors the radius of the feed roll by measuring the time between pulses created by Hall-effect devices and magnets on the feed spindle and metering roller.

The brakes use an internal, centrifugal cooling fan and ventilation slots to keep the brakes cool. For example, the MBL-5.5, with a 5.5-in. OD, can dissipate 4,700 W for 10 sec; on a continuous basis, it can dissipate 1,700 W at 8,000 rpm. The brakes come with outside diameters ranging from 1.5 to 12 in., and handle 4,000 to 20,000 rpm. The brakes are powered by a 24-V power supply.

© 2012 Penton Media, Inc.

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