These issues often emerge during power failures to the stepper motors or servo motors that move in precise angles, such as in robot arms or grippers. Without power, these motors cannot generate sufficient holding torque to maintain their position against external forces. When gravitational force or other mechanical force exceeds the motor's detent torque, uncontrollable movements can occur, potentially compromising product quality, dosage accuracy, or equipment calibration.
| Dispensing | Transferring | Pick and Place |
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On an electromagnetic brake type stepper motor, a built-in, power-off-activated electromagnetic brake is connected to the rear shaft of the motor. The brake operates with a 24 VDC power supply. When 24 VDC is supplied to the brake leads, it excites the electromagnet in the brake, which magnetically attracts the armature against the force of the spring. This releases the brake. When no voltage is supplied, the electromagnet stops working, and the spring presses the armature onto the brake hub. This engages the brake and holds the motor shaft in position. For certain products, such as the AZ Series hybrid step-servo motors and actuators, the electromagnetic brake control is done automatically by the dedicated driver. |
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Here's a video explanation:
- Hold the Vertical Z-Axis in Place During Power Failure
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When transporting a blood sample or chemical reagent, an electromagnetic brake type motor prevents the Z-axis end-effector from failing in case of loss of power. If the sample were to break and spill, it would cause unexpected downtime to sterilize the machine and replace damaged components.
Side Note: When using an AZ Series hybrid step-servo motor with built-in multi-turn mechanical absolute encoder, a homing routine is not necessary after a power loss.
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- Minimize Vibrations for Clear Imaging
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In an inspection application, an electromagnetic brake type motor can hold the load still and prevent minute movements for a clearer image. When using servo lock mode or standstill holding current for stepper motors (without an electromagnetic brake), there's potential for the motor shaft to ring and vibrate slightly back and forth between poles until it settles into its target position (undetectable with the naked eye). Side Note: Learn more about stepper motor vibration and tips to minimize it. |
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- Prevent Backdriving for Grippers During Power Failure
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Based on its design, a gripper in a pick and place application can potentially be back-driven by its load when powered down. An electromagnetic brake type motor can maintain the holding force in the gripper and prevent parts from slipping out of its grasp. Side Note: It's also better to use multiple torque limit settings to enhance a gripping operation. Learn how to apply multiple torque limit settings in a gripping operation. |
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- Keep Chamber Doors Closed and Locked
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In a manufacturing, an electromagnetic brake type motor keeps doors and gates closed and locked, preventing operators from accessing a restricted area during a test or machining process. When the door is lifted up in the open position, an electromagnetic brake type motor prevents the door from falling to the closed position and potentially injuring someone's hand. The electromangetic brake can also be used to keep the door in the open position for maintenance purposes. Side Note: to enhance safety further, a certified STO "Safe Torque Off" function is available with our AZ Series and BLV Series R-Type drivers. |
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- Energy Savings and Temperature Reduction
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When not using a brake, an ungeared stepper or servo typically requires power to generate a holding force to prevent an external force from moving the motor shaft. For applications like processing or transferring biological samples, the additional heat generated can be too much and destroy the samples. A power-off-activated electromagnetic brake type motor can hold its shaft in position while reducing temperature and power consumption. Side Note: sometimes, friction within the bearing or gears can provide some detent torque that can be used for holding a light load in place. However, this is approximately 2~5% of rated torque and is not guaranteed. |
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Here's a comparison table that explains the benefits of using a motor with a built-in electromagnetic brake.
| Feature | With Built-in Electromagnetic Brake | Without Built-in Brake |
| Safety During Power Failure | Engages automatically, preventing movement | May move unexpectedly, posing risks to patient and caregiver |
| Precision Positioning | Quick stopping and holding for accurate positioning | May require additional mechanisms, potentially less precise |
| Space Requirements | Compact, integrated design saves space | May need external brake, increasing space needs |
| Energy Efficiency | No power necessary to hold position | May consume power for holding, reducing efficiency |
| Regulatory Compliance | Supports meeting safety standards, easier certification | May require additional validation for separate components |
| Maintenance | Potentially fewer components, higher reliability | More components, possibly higher maintenance needs |
Please visit our medical industry page for suggested products.
| Additional Electromagnetic Brake Tips: |
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👍 Electromagnetic brake type motors are also great at preventing back-driving in AGVs and AMRs. Remember, once you back-drive a motor, it becomes a generator. I still remember a customer telling me that he was pushing an AGV up a ramp, hearing a "pop", and seeing smoke from the driver. The "pop" sound was likely from the electrolytic capacitors. If you see smoke from the driver, it's time to replace the driver. ⛔ Don't use the electromagnetic brake to stop the motor, as it would shorten the life of the brake due to excessive wear and tear from friction. To prolong brake life, stop the motor first, then engage the brake to hold it in position. In vertical motion applications, this timing could be a little tricky if the brake control isn't automatic, so refer to the timing charts in the manual. FYI: Below are the estimated lifespans for reference. The estimated lifespan of electromagnetic brakes can differ depending on the type of motor, load, and speed.
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As always, our knowledgeable tech support engineers are available to help with questions about applications that involve an electromagnetic brake.
