I have been tasked with building a control system for a machine we have. On this machine are nine VFD's whose motors are connected to electric brakes, six of which are used to stop individual, massive inertial loads.
General shutdown procedure is rather than a three wire circuit I use a pushbutton connected to a plc input. When pushed, it initiates a stop command, ramping all motors to a stop, then deenergizing the brake, then firing a relay turning the machine off.
My concern here is that if power is lost to the machine, the brakes will immediately engage causing mechanical damage.
My idea is this but I'm looking for a better one: feed the plc and all of the brake circuits with a UPS. In addition to the normal stop input, wire the main control power to another input and if that input goes low, the stop circuit is initiated in the same manner as above. The UPS would have to be sized to power the plc and brakes through the shutdown process.
Any feedback on this would be appreciated. Thanks.
General shutdown procedure is rather than a three wire circuit I use a pushbutton connected to a plc input. When pushed, it initiates a stop command, ramping all motors to a stop, then deenergizing the brake, then firing a relay turning the machine off.
My concern here is that if power is lost to the machine, the brakes will immediately engage causing mechanical damage.
My idea is this but I'm looking for a better one: feed the plc and all of the brake circuits with a UPS. In addition to the normal stop input, wire the main control power to another input and if that input goes low, the stop circuit is initiated in the same manner as above. The UPS would have to be sized to power the plc and brakes through the shutdown process.
Any feedback on this would be appreciated. Thanks.