Braked Stepper Motor

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Steve
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Braked Stepper Motor

Post by Steve » Wed 13 Jan , 2010 11:16 am

This post covers the Braked stepper motors fitted to Denford Machines:

The motor has a double ended shaft and at the rear of the motor a hexagonal nut is secured to the shaft.

Around this nut a fibre washer is fitted which has a hexagonal hole in the middle. When the brake is released the motor shaft revolves and the nut on the rear of the shaft revolves with it also driving the fibre washer.

When the brake is on the fibre washer is clamped to the end face of the motor by spring pressure within the brake solenoid.

The fibre washer being clamped prevents the motor shaft turning.

The Brake units are a solenoid powered by 24V DC. When energised the solonoid compresses a spring releasing the fibre washer.

The first Image shows the Brake removed and the fibre washer inside the brake unit with the Hexagonal hole through it.
The second image shows the nut secured to the shaft at the rear of the unit.
The third photo shows the assembled brake unit.
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Steve
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Posts: 1288
Joined: Tue 21 Feb , 2006 16:15 pm
Location: Denford UK

Re: Braked Stepper Motor

Post by Steve » Wed 13 Jan , 2010 11:29 am

Faults that can occur are:

The brake never releases because the 24V power supply has failed. (On older Compact routers this supply was created by rectifying the AC supply with diodes).

The brake never releases because one of the two brake wires is broken.

Sometimes the Nut fitted to the rear shaft of the motor is fitted too close to the motor body or too far away from the motor. In either case the nut will rub on the motor or the brake and can cause the motor to stall.

The brake is only fitted to prevent the Z axis falling under gravity when the machine is not powered up or to prevent the tool pulling the z axis down into the job if the E - Stop is pressed when the tool is cutting.

For fault finding the machine can be run with the brake removed from the rear of the motor and the machine should function without problem.

The brake on:

When the power is disconnected

For the first few seconds after power has been connected untill the drives are energised

When the machine E-Stop is pressed.

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