A motor soft start-stop unit can benefit applications like
conveyors, pumps, fans, overhead traveling cranes, and automatic doors that don’t need high levels of start-up torque and run at constant speeds. Controlled and predictable speed changes also improve operator safety. Motor starting and stopping speeds are guided using solid- state devices like silicon- controlled rectifiers (SCRs) that control the voltage and the current to the motor. Once the motor is fully started, the SCRs are bypassed using a contactor to improve operational efficiency.
Figure 2: Two linear motor stages can be stacked to support cartesian motion. (Image source: Omron)
Soft start-stop units like the Alistart 22 family from
shaft designs, linear motors can provide higher positioning accuracy and faster movement. The mechanical parts of linear motion stages can be packaged in highly enclosed structures for environmental protection. Omron offers linear motion stages based on iron core motors ranging from 30 mm active magnet width and three coils to 110 mm active magnet width and 15 coils. They are rated to deliver from 48 Newtons (N) to 760 N of force. The R88L-EA-AF-0303-0686 linear actuator motor is available in 230 V and 400 V models. It has a rated force of 48 N and a peak force of 105 N. It can be driven with the R88D-KN02H-ECT servo
driver that includes EtherCAT communication for integration into industrial networks. Two linear motion stages can be stacked to provide motion in a cartesian coordinate system (Figure 2). Soft start-stop units While VFDs/VSDs and servo drives control motors' speed and torque while running, soft start-stop units limit current inrush when a motor is started to protect the motor and provide a smooth ramp up in speed and torque. They provide smooth ramp downs in speed as the motor is stopped. They also protect the mechanical components in the system from damaging torque spikes when starting or stopping.
Schneider Electric can handle a wide range of three-phase asynchronous motors from 4 kW to 400 kW. They include Class 10 motor overload and thermal protection, providing a fast- tripping time of 8 to 10 seconds. The power ratings of soft start- stop units often depend on the motor's operating voltage. For example, Schneider Electric’s ATS22D17S6U unit can handle motors rated for 3 hp with 208 V power, 5 hp with 230 V power, 10 hp with 460 V power, and 15 hp with 575 V power (Figure 3). It requires 110 V AC 50/60 Hz power for the control circuitry.
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