Pancake Servo Motor Repair
As one of America’s leading servo motor repair shops, we service a full line of pancake servo motor brands. Our servo repair and refurbishment services are recognized throughout the industry for quality repairs, fast turnaround and unrivaled service excellence. Fill out our online form, or call us directly, for a fast, free pancake servo motor repair quote.
About Pancake Servo Motors
CNC machines have been around for quite a while, and each is designed for different purpose. Some motors are built for efficiency, others for torque. In the instance of disc motors, or servodisc motors – most commonly referred to as pancake servo motors – the goal is to achieve as much torque as possible while limiting the inertia of the rotor.
Certain applications call for high inertia, which is why spindle motors, or anything involved in a cutting operation, is designed to have high inertia. Inertia in this case is referring to the stored force associated with rotation. The potential for high inertia means a spindle motor can do its job efficiently and not get tripped up by particularly hard metals, because once the motor gets up to speed it requires a tremendous amount of force to slow it down.
Pancake servo motors are actually trying to limit their inertia, so when the power fed to the servo motor is increased or reduced, there is very little internal resistance to the change in speed.
Pancake Servo Motor Repair
Pancake motors present a unique set of challenges within the servo motor repair field. Essentially, they are DC brush type motors that are flat – like a pancake. The motor armatures are thin discs of copper, and are insulated by a small amount of Mylar.
Because of the small nature of the armatures, these servo motors are equipped with very powerful permanent magnet field frames which are specially magnetized to yield the highest possible torque.
Our process for pancake servo repair is modeled after our DC servo motor repair procedures, with some protocol changes.
1. Pancake Servo Motor Evaluation – the servo motor is reviewed to check the integrity of all the specialized components. We test for the following conditions during evaluation:
- Motor armatures and tach armatures are inspected for concentricity, any bends or mechanical irregularities can cause more damage to the servo motor if it is run under power.
- Bearings and fits are checked with the same precision as a normal servo motor, with an especially close look at pre-load. Pancake servo motor bearings must have the proper pre-load or heat expansion may create catastrophic mechanical conditions.
- Brushes are researched to ensure that we can obtain properly sized and rated brushes. Pancake servo motor brushes are much longer and thinner than a standard brush.
Two prominent Kollmorgen pancake servo motors, which are a marvel of engineering. We also service much smaller motors, which are about the size of these motors tachometers.
2. Pancake Servo Motor Repair Procedures – efforts specific to pancake servo motors are carried out, sometimes as a portion of the evaluation. Pancake motors represent a unique challenge, and sometimes a quote for repair cannot be provided until we have successfully completed some of the more difficult repair procedures.
- Armature reconditioning is very different from normal DC servo motor repair. It is impossible to undercut and turn down the commutator because the commutator essentially is the armature and is much to thin. We meticulously clean both the motor and tach armatures to get rid of any built-up carbon and search for blown traces.
- In some cases, the permanent magnets of the field frame need to be re-epoxied to the frame of the motor. We can both re-secure and re-magnetize the field magnets.
- Pancake servo motors are so delicate that no chance is taken with mechanical tolerances. Often, we will install a bearing with an integrated snap-ring to ensure that the disc armature will run true. Even the smallest wobble can spell disaster for a pancake servo.
A blown disc armature on a pancake servo motor that is beyond repair, and a brand new armature from our stock inventory. Both discs are from a Parvex disc servo motor.
3. Pancake Servo Motor Repair Testing – Preliminary tests don’t take place until our technicians are convinced that a dynamic test will not in any way cause damage to the servo motor. Sometimes it is impossible to perform these tests without rebuilding the motor until we have successfully completed some of the more difficult repair procedures.
- Pancake servo motors are driven under power to evaluate the mechanical operation of the bearings and integrity of the shaft.
- Brush wear and magnet strength can be evaluated based on motor BEMF wave forms and tach waveforms.
- Each portion of the pancake servo motor is meggered, and resistances are checked with a milliohm meter to accurately determine if an armature is good, or even if it run correctly.
- Any additional demagnetization and re-magnetization of the field magnets are completed.
Single unit brush holders typical of a pancake servo motor. The set closer together is for the tachometer, and the one further apart powers the motor. The green painted armature below is for a standard pancake tachometer.
4. Pancake Servo Motor Repair Assembly – Assembly occurs once we have isolated each issue with your servo motor and addressed it accordingly.
- New brushes and brush caps are installed, along with brush-holder in some cases.
- Bearings are replaced with new sealed style bearings – pancake servo motors bearings are much closer to the carbon contamination created by brushes, which makes the use of sealed bearings essential to extending the service life of the servo motor.
- Field frames are recharged on every pancake servo motor, no matter what!
Left are two pancake style tachometers – one is brand new and one is refurbished – can you tell which is which? Right picture is a re-assembled pancake motor added to depict how close the disc armature runs to the permanent magnets.
5. Final Pancake Servo Motor Testing – Final servo testing includes a recap of all the initial tests. In many cases, it is also the first time dynamic testing can be performed.
- Each servo motor is dynamically tested to check for proper BEMF and tachometer voltage levels.
- Feedback devices are re-installed and tuned for proper operation. In many cases encoder are replaced with retrofits, which have signals that must be cross-referenced for accuracy.
- Neutral is set – a concept by which we ensure that a DC brush type motor runs properly and with the same characteristics in both directions.
- Finally, if all other factors are equal, we check to make sure that there is no vibration, brush noise, or bearing noise. Even small inconsistencies can mean the destruction of a pancake servo motor.
6. Pancake Servo Motor Nameplates – Nameplates re-installed on pancake motors are more challenging than typical servos because the motors are so oddly shaped! Nameplates record information including the servo motor manufacturer, part number, and information about this repair’s Servotech job number so that the motor, and the repair, can be referenced in the future. Typically, if a customer has one pancake servo motor, they will have many. Most motor shops lack the capability to repair disc/pancake style DC servo motors. Servotech is unique in that we have not only the capability, but also a stockpile or parts and specialized tools to ensure that our repairs return motors to factory condition.