A hysteresis brake and dc power supply from Placid Industries, Lake Placid, N.Y., applies torque loads for testing PaintEater paint-prep tools. The PaintEater from Wagner Spray Tech Corp., Minneapolis, removes paint chips, feathers edges, and abrades the surface of old paint in preparation for repainting. Unloaded output speed is 2,500 rpm, which drops to 2,000 rpm with a 110-oz.-in. load.
The hysteresis brake handles the relatively high speed and low torque. A PLC sends a 0-to-10-Vdc signal to the brake power supply. The supply correspondingly adjusts output current to simulate various user loadings. Torque scales with input current and is independent of speed. Closed-loop torque feedback isn't needed, minimizing cost. Hysteresis brakes, unlike friction types, produce torque solely with a magnetic field. There is no contact between moving parts and thus no wear and torque loss with usage.
Cogging (pulsing torque) had been a major drawback of hysteresis brakes. Such brakes tend to cog when input current drops significantly while the shaft is stopped or slowly moving. Cogging "locks" the shaft into about 12 to 20 equally spaced angular positions.
Placid Industries' patented Cog-Buster technology zeros out torque pulses within one shaft revolution to automatically stop cogging. Without Cog-Buster, a brake will cog until manually decogged.