MBZ SERIES - MAGNETIC BRAKE ZERO COGGING

One of the undesirable characteristics of conventional hysteresis brakes is the cogging phenomenon. The MBS MBZ series brakes have the ability to reduce the cogging to negligible levels in less than a second and without rotating the brake's drag ring.

 

WHAT IS COGGING?

Cogging is a ripple torque produced by a hysteresis brake without any current being applied to the brake. It is caused by alternating magnetic fields of residual magnetism in the brake’s drag ring when the current is removed while the drag ring remains stationary. The number of alternating magnetic fields in the circumference of the drag ring will be equal to the number of poles in the stators of the brake.

 

A pulsating torque will immediately be evident if the brake shaft of a cogged brake is rotated manually. Although reapplying the current to the brake will eliminate the cogging, it will also provide a resistive torque that a motor may not be able to overcome. The ripple torque may be as high as 25% of the brake's maximum torque.  

 

There are two methods to degauss or de-cog a brake: dynamic de-cogging and static de-cogging.

 

DYNAMIC DE-COGGING

To avoid the cogging phenomenon or dynamically de-cogg a brake, one must ramp the current to the brake to zero, while the drag ring is still rotating. This method eliminates the alternating magnetic fields in the drag ring and therefore the cogging.

When the available driving torque is insufficient to overcome the cogging torque, dynamic de-cogging may not be possible. The MBS controller provides a solution to this problem and allows the customer to perform static de-cogging. The static de-cog command may be executed either automatically or manually.

 

STATIC DE-COGGING

Static de-cogging is degaussing the magnetic field in the brake, while the brake is stationary. For all brake sizes from MBZ-8.7 and smaller, this operation takes less than a second.

 

If configured for Manual De-cogging (default configuration), the operator commands the de-cog cycle with a momentary switch connected to the controller of the brake. The de-cog function is only operational when the brake has come to a full stop for approximately 2 seconds, and zero current is applied to the brake. 

 

If configured for Automatic De-cogging (operator selectable), the MBS controller will automatically enter the de-cogging cycle when the brake comes to a stop, and the current to the brake is brought to zero.

 

 

The MBZ series brakes, in addition to the de-cogging feature, have all the features of the MBL series brakes.