Stepper Motors

By: Anaheim Automation  06-Dec-2011
Keywords: Motion Control, Stepper Motors, Stepper Motor

Common Causes for Stepper Motors and/or Stepper Driver Failure
NOTE: Always read the specification sheet/user's guide that accompanies each product

Problem: Intermittent or erratic stepper motors or drivers function.

Solution: This is the most common cause of failure and one of the most difficult to detect. Start by checking to insure that all connections are tight between stepper motors and drivers. Evidence of discoloration at the terminals/connections, may indicate a loose connection. When replacing a stepper motor, driver or Driver Pack in a motion control system, be sure to inspect all terminal blocks and connectors. Check cabling/wiring for accuracy. Stress stepper motor wiring and connections for worse conditions and check with an ohmmeter.

Problem: Stepper motor wires were disconnected while the driver was powered up.

Solution: Avoid performing any service to the stepper motors or drivers while the power is on, especially in regard to motor connections. This precaution is imperative for both the driver, as well as the technician/installer.

Problem: Poor system performance.

Solution: Check to see if the wire/cables are too long. Keep wire/cable to the stepper motors under 25 feet in length. For applications where the wiring from the stepper motors to the stepper drivers exceeds 25 feet, please contact the factory for instructions, as it is likely that transient voltage protection devices will be required. Another possibility is that the stepper motor lead wires are of a gauge that is too small. Do not match your cable wires to the gauge size the stepper motor lead wires. Anaheim Automation suggests using a shielded cable for such wiring (purchased separately). Additionally, check the age of your stepper motor, as with time and use, stepper motors lose some of their magnetism which affects performance. Typically one can expect 10,000 operating hours for stepper motors (approximately 4.8 years, running one eight-hour shift per work day). Also, make certain that your stepper motor and driver combination is a good match for your application. Contact the factory, should you have any concerns.

Problem: The stepper motor has a shorted winding or a short to the motor case.

Solution: It is likely that you have a defective stepper motor. Do not attempt to repair motors. Opening the stepper motor case may de-magnetize the motor, causing poor performance. Opening of the stepper motor case will also void your warranty. The motor windings can be tested with an ohmmeter. As a rule of thumb, if the stepper motor is a frame size of NEMA 08, 11, 14, 15, 17, 23, or 34 and the warranty period has expired, it is not cost-effective to return these stepper motors for repair. Call the factory if your suspect a defective stepper motor that is still under warranty, or if it is a NEMA size 42 or a K-series motor.

Problem: The stepper motor driver or Driver Pack is over-heating.

Solution: Ventilation and cooling accommodations are essential - failure to provide adequate airflow will affect the stepper motor driver's performance and will shorten the life of the driver. Keep driver temperatures below 60 degrees Celsius. To maintain good airflow, use fans, heat sink material, and base plates, so not to exceed the maximum temperature rating of the stepper motors, drivers or controllers. Be mindful of temperatures inside cabinets and enclosures where stepper drivers may be mounted.

Problem: Environmental factors are less than ideal.

Solution: Environmental factors, such as welding, chemical vapors, moisture, humidity, dust, etc., can damage both the electronics and the stepper motors. Protect drivers, controllers and stepper motors from environments that are corrosive, contain voltage spikes, or prevent good ventilation. Anaheim Automation offers products in several line voltage ranges. For AC lines that contain voltage spikes, a line regulator (filter) will likely be required.

Problem: Pulse rates (Clock or Step) to the driver are too high.

Solution: The typical half-step driver can drive stepper motors at a maximum rate of 20,000 pulse per second. Pulse rates of above 60,000 pulses per second can damage the driver. See individual specification sheets for the motor and driver combination for best performance.

Problem: The stepper motor is stalling.

Solution: In some cases, stalling the motor causes a large voltage spike that often damages the phase transistors on the driver. Some drivers are designed to protect itself from such an occurrence. If not, Transient Suppression Devices can be added externally. Consult the factory for further information.

Problem: The stepper motor is back-driving the driver.

Solution: A stepper motor that is being turned by a load creates a back EMF voltage on the driver. Higher speeds will produce higher voltage levels. If the rotational speed gets very high, this voltage might cause damage to the driver. This is especially dangerous when the motor is back-driven while the driver is still on. Put a mechanical stop or brake in applications that might be subject to these phenomena.

General Safety Considerations for Stepper Motor Applications

The following safety considerations must be observed during all phases of operation, service and repair. Failure to comply with these precautions violates safety standards of design, manufacture, and intended use of stepper motors, drivers and controllers. Anaheim Automation, Inc. assumes no liability for the customer's failure to comply with these requirements. Even well built products, operated or installed improperly, can be hazardous. Safety precautions must be observed by the user with respect to the load and operating environment. The customer is responsible for proper selection, installation and operation of the products purchased from Anaheim Automation, Inc.

• Use caution when handling, testing, and adjusting during installation, set-up and operation • Service should not be performed with power applied • Exposed circuitry should be properly guarded or enclosed to prevent unauthorized human contact with live circuitry • All products should be securely mounted and adequately grounded • Provide adequate air flow and heat dissipation • Do not operate in the presence of flammable gases, vapors, liquids or dust

NOTE: Please Use a RMA Form should you need to return a product for REPAIR. This form can be found in Support, Forms, RMA Request on this web site.

Keywords: Anaheim Automation, Lead Wires, Motion Control, Motor Windings, Stepper Motor, Stepper Motors,

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