Servo Motor Services

Stop overpaying for OEM servo motors!

Are you buying your servo motors from your machine manufacturer and paying way too much money?  Have you called the servo motor manufacturer and been told "we cannot sell you this motor, call your OEM"?  Before you give up hope, there is a strong possibility you can obtain a replacement motor for much less!

Most OEM servo motors have had modifications made to them specific to their application.  These modifications can range from something as simple as connector pin assignments to something as involved as installing special feedback in the servo.  In order to determine the modifications made to the motor there are a few pieces of information you need.

Try to obtain a datasheet or brochure on the series of servo motors from the motor manufacturer matching your servo.  This will very often give you a rubric to break down you servo motor part number to define the specific properties of your servo.  Now you will need the part number off of your motor.  Break down your part number using the rubric and see what has been changed.  You will find that a letter or number in your part number is not listed as an option in the rubric.  That usually corresponds to what is different about your servo.  Now for some detective work.

If the change in the part number corresponds to something like a connector or seal you are doing great.  Order a servo motor from the servo manufacturer with the closest matching part number and buy the seal or connector separately.  Remove the stock seal, connector, etc. and install the unique one and you just saved a lot of money!

Sometimes the part number will have extra characters at the end or the unique sections of the part number will correspond to something complicated such as motor torque or shaft dimensions.  Dig deeper into you datasheet, comparing all physical and electrical specifications of your servo to a stock servo, and you should find the modification.

Hopefully you find what makes your OEM servo motor unique and you can be done with drastic overcharging and long lead times by buying your servo motor straight from the manufacturer.

 

 

 

If you need assistance in locating a direct replacement for your OEM servo motor our technicians are here to help!  And if a replacement does not exist we are your best source for refurbishing your servo motors to new condition and still avoid overpaying for OEM!

 

 

 

Resolver Wiring; Colors & Functions

If you ever plan to replace or test a resolver then you need to know the functions of each wire.  This can be very difficult to determine with out a little knowledge and a voltmeter.  There is an industry standard for resolver wire colors that most manufacturers choose to use.  These colors are as follows; Sometimes Yellow/White can be used in the place of Black/White for Excitation-.  These are industry standard wire colors but you will come across other brands of resolvers with their own proprietary color designations.  When this happens you will need to use a voltmeter to assist you in determining wire color versus function.Almost all resolvers have 6 leads.  Use a voltmeter to ring out the leads and determine which 3 pairs of wire are circuits.  Then record the resistance of each circuit.  The Cos and Sin circuit will have the same resistance, so the circuit with the different resistance will be your excitation circuit.  If any circuits ring open, or all three circuits have different resistances then your resolver could have a damaged winding and need to be replaced/rebuilt.These are some basic tips on how to determine a resolvers wiring.  In order to continue on and designate exact wire functions on nonstandard wire colors you will need to excite the windings with the proper frequency and use an oscilloscope.

Servo Motor Connectors; Where Can I Find Them!?!

Your servo motor needs a new connector.  The connector is cracked and the pins are all bent.  You look at it and think, “Where am I ever going to find this plug?”  And even if you find the plug and get it on time, can it be changed easily?

 

Connectors can quickly become a headache.  With so many styles, manufacturers, and specific needs there are millions of plugs in production to choose from.  Finding your connector can be extremely difficult if you do not know how to search.  Once you have found your connector, do you have the tooling you need to install it correctly?  Do you have the information recorded when you disconnect the old connector to connect the new one? 

 

• The first step to finding your connector is refining your search.  This will limit the number if connectors to search through by specific characteristics.  Many online companies that sell connectors will let you limit your search by choosing variables such as rated current, shape, number of pins, etc.  If you know the manufacturer of you connector (give it a good look over) then you can limit your search or go straight to that manufacturers online site.  If you can obtain a manufacturers part number, many online sites will cross it to their own part number.  If at all possible, get a datasheet and verify dimensions before purchasing, you don’t want a close match, you want an exact match.

 

• There are some tools that are necessary to install connectors on your servo motor.  You will need a soldering iron to solder the pins and sockets.  Even if they are crimp pins, many people will solder the crimp to strengthen the joint and prevent fraying.  If the pins need to be crimped invest in a crimper for that style connector.  Many connectors are threaded together and you will need wrenches and pliers. 

 

• Always document the connector wiring before removing the old one.  Write down wire colors relative to pin numbers.  If possible also document wire functions to pin number as colors are not always easy to differentiate.  Most people forget to document the orientation of the connector in relation to the motor, and also the orientation of the connector hub to the housing of the connector.  If these are not correct you may not realize it until you motor is reinstalled into your machine and now the cable does not reach or mate with your motor.

 

These are some considerations to make when changing your connectors on you servo motor.  There are many good places to shop for connectors, and prices can fluctuate greatly, so shop around.  If you are having someone else change your connectors make sure they are replacing you old connector with a proper match.  Many repair facilities will use unsealed or lower quality replacement connectors resulting in more problems down the road for you.

 

 

 

 

 

 

Disassembling your own DC Servo Motor

So you think you’ve got what it takes to rebuild your broken DC servo motor.  Just a rotor with a couple bearings right?  Wrong, there are many factors to consider before disassembling your own DC servo motor.

 

• Capability to test the armature insulation correctly.

There are special testers used to test the insulation that protects the winding from grounding out to the iron on the armature.  It is very important that the insulation be up to standard.  When the motor is being run under load there is potential for electricity to go to ground.  If there is any exposed copper on the winding this would be a high potential for grounding out during operation.  Any area were the insulation is scratched will have a high potential to corrode over time and fail.

 

• Capability to test the armature circuit correctly.

There is also special testing equipment to test each circuit of the armature insuring that the windings are going to work to specification.  Special attention needs to be paid to the commutator.  If the commutator is worn or burned it will need to be turned in a lathe or replaced.

 

• Damaging the electrical windings as you separate the armature from the field frame.

Removing the armature is a delicate process, which is compounded by the magnetic force of the field frame.  The exposed wires, and commutator are extremely prone to getting nicked or damaged during the disassembly process.  Even minor physical damage to the circuit of the armature can cause a motor to malfunction and burn up.

 

• Separating the armature from its magnetic field of the fields frame(magnets),causing demagnetization

There are many types of magnets. The most popular types used in servo motors are Neodymium Iron Boron (NdFeB or NIB),Samarium Cobalt (SmCo), Alnico, Ceramic, Ferrite and Rare Earth. Certain magnet types require that their fields not be broken. If a motor or tachometer armature is removed from the wrong type of field frame, the magnets will loose their strength effectively ruining the servo. The only way to rectify demagnetized field frames on a disassembled servo motor is to recharge the magnets. Otherwise the servo will never run properly.

 

• Damaging the tachometer armature as you attempt to remove it from the motor armature

Often, as you try to take the Tachometer off of the motor shaft it can be very hard to remove because of corrosion and tight tolerances. We have made several special removal tools to take the tachometer armatures off to prevent destroying them. The windings on a tachometer armature are smaller than the hairs on your head, and much less resilient to forces applied to them.  

 

• Assembling the field frame on the brush rigging incorrectly

     The relative position of the field frame to the brush rigging needs to be correct.  If this relationship is not correct the motor will not commutate correctly resulting in torque loss, over current, and motor failure.

 

 

   

 These are a few of the important things to know before you start to take apart your own DC Servo Motor.  If you decided that you want your motor professionally repaired then send it to Servotech Inc.  We have all the necessary knowledge and equipment to rebuild you DC servo motor.

Servo Motor Torque Loss

Your servo motor does not have the power it once had.  You are starting to encounter current and torque alarms on your machine.  You check the couplings, bearings, maybe even swap drives.  Nothing seems wrong and the problem is probably in the motor.  Now what?

There are several reasons that your servo could be losing torque.  Figuring out what is wrong with your motor will determine how difficult it is to fix, and who is even capable of fixing it.

•  Does your servo motor have a brake?  If there is a brake in your motor then you need to check the voltage going to the brake.  Most motors will have the brake voltage written on the label.  If the brake is not opened when the motor runs, then you will lose significant torque and also destroy the brake.  This is a common problem and is often caused by faulty relays in the cabinet.

• Are your servos magnets demagnetized?  This can be determined by checking the BEMF of the servo, which will probably require you to send the motor out to be evaluated.  If the servo is demagnetized then you will need to find a company that can re-magnetize your servos' magnets.

• Has your Servo ever been disassembled?  If the encoder has been removed and reinstalled the alignment might be off.  A bad alignment can cause you servo to run, but run poorly drawing high current.  If this is your problem then you need to have your servo serviced and realigned.

Torque Loss is a common problem.  The root cause needs to be determined so that you can be sure you are fixing the right problem.  If you find you have to send your servo out for repair, it is best to make sure they have the equipment to do the job.

 

 

 

 

 

 

 If you don't know what to do or where to have your servo repaired, Servotech has the equipment and knowledge to restore your servo motors torque to its original factory specifications.

 

Resolver Overspeed

Your servo has run away and your drive pops an error code.  You write down the error code and look it up in the manual.  The code corresponds to a "resolver overspeed" alarm.  Next to that is written "check the feedback cables" as a probable solution.  You replace the cable and get the same alarm, now what?

Resolver overspeed is a very common alarm, and it is one that can have many causes.  Many of these causes are easy to fix, and eliminating the different causes can help you determine what part of your system needs repair.

Are your cables properly shielded?  Your cables should have an internal shield that is properly grounded.  Shields are usually grounded directly to the inside of a cabinet.  Resolver based systems are very sensitive to noise and can be prone to alarms if not properly shielded.

Has your servo been disassembled?  Have you had your motor rebuilt or tried to do it yourself?  If so was the resolver properly aligned to the motor?  If for any reason your resolver has changed its position in relation to your motor your system will not run.  A misaligned resolver can cause many alarms including resolver overspeed.

Has your wiring been changed?  If you have swapped drives or changed cables then your wires could have been connected incorrectly.  Swapping resolver wires can cause the resolver to swap direction, change to location of the zero position, or not function at all.  Miswired resolvers can cause overspeed alarms.

These are some causes for resolver overspeed.  In many cases resolver overspeed is caused by something other than a bad servo.  If you are having trouble with this alarm you should try to eliminate these possible causes before you send anything out for repair.

How to Prevent Damage to Your Servo When Removing a Coupling

The Coupling on your motors shaft needs to be removed or put back on.  You grab a hammer and some prybars....

First off, put the hammer and the prybars back.  Your servo has very sensitive feedback sensors installed in the motor.  These devices are attached directly to the shaft and are easily damaged.  Any hammering could break the glass of an encoder.  Prying on the coupling could also break glass or drive the rotor of a resolver into the servomotors endbell destroying it.  In order to remove your coupling easily, there are a few things to evaluate about it.

Are there any setscrews or bolts on the end of the shaft.  Take the time to clean the coupling and look.  If you find one setscrew there are probably more.  Pulling the coupling off of the shaft without removing setscrews will damage the shaft.

Does your coupling have threaded holes that can be used as backdrives?  Many couplings have compression rings that can be pushed apart using the backdrive holes.  This will allow you to pull the coupling off by hand.

Use a puller, not prybars.  Using a puller will move the coupling in relation to the shaft.  Prybars will pull the shaft and the coupling away from the motor possibly damaging the bearings and/or feedback.  If you put alot of force on the puller and the coupling still will not budge then try adding some quick heat to the coupling.  If you can heat the coupling before the shaft the expansion will help free the coupling.

These are some tips to remove a coupling from the shaft while minimizing possible damage to your servomotor.  

Tips on Using Slings to Remove and Install your Heavy Servo or Spindle Motor

Your motor has failed and you need to remove it from your machine.  You have disconnected all the electrical, dissconnected the coupling, cursed the engineer who designed the machine, and are now ready to remove the motor.  There is just one obstacle left however, the motor weighs way more than you can lift by hand.

You decide to use a forklift or ceiling crane to lift the motor out of the machine.  You see that the motor has one or two eye-bolts that you can attach slings to.  Just connect the motor to the crane and lift right?  Almost, but there are a few things you must do to insure your personal safety and the safety of the motor.

Slings are specifically rated for certain loads.  These loads vary depending on the manner in which you utilize the sling.  These loads should be documented on the sling lable.  If the lable is missing or you are using a sub-par sling you should consider throwing it away and investing in proper slings.

Learn the right and wrong ways to attach a sling.  Wear-flex has a webpage on the proper use of their slings.   Knowing when a sling is being used improperly will reduce the likleyhood of undue strain leading to sling failure.

Always use one sling per eye-blot.  Never loop the sling through two eye-bolts.  This mistake is common.  When the sling loops from one eye-bolt to another it puts force on the bolts at an improper angle that can lead to them bending or breaking.  Always lift an eye-bolt straight up from the top of the bolt, and check that the bolt is tight before lifting.

These are some tips on safely lifting your motor out of your machine and putting it back in. 

What to Consider When Your Motor Has a Bad Bearing Fit

Your motor has a strong vibration or knocking sound.  You send it somewhere for repair and you are told that the bearing fit is no good.  You get a quote to change the bearings and repair the bearing fit.  Problem solved you say....  Then your servo is returned and fails again.  What is so difficult about fixing a bearing fit?

Failure of a bearing fit is a common problem with all electric motors.  Bearing fits fail when the fit is not the correct bore, the bearing was incorrectly installed, or the bearing seized.  If a bearing fit fails this can lead to many other problems with your servo motor.

-Feedback devices are very sensitive and are damaged easily by oscillation.    Encoders often have glass scales that shatter and resolvers have windings that are damaged when their axis of rotation is not perfectly central.

-Rotor shafts can bend or break.  Servos need to run true and broken shafts can occur under the armature where they are often missed until the motor is under load in your machine.

-Stator Laminations can be damaged resulting in rubs and grounded power leads.  The air gap between rotor and stator is small, so when there is an oscillation in the rotor it will bang into the stator laminations.  Bending the laminations can cause high spots that rub and also cause the lamination to pinch the coil under it shorting the motor windings to ground.

When your servo motor has a failed bearing fit be cautious where you have it repaired.  Regular motor shops will not be capable of evaluating or repairing the feedback on your servo.  Most places will see a failed fit and look no further.  Being aware of the side effects of a bad fit will improve the likelihood that your servo gets properly repaired the first time.

Minimizing Noise on Your Servo System

Your servo suffers from intermittent failure, feedback loss, runs choppy, or trips out on some sort of encoder error. Could electrical noise be the culprit?

 

Electrical noise is present in every electrical system. It can disrupt the feedback signals (especially with resolvers) on the motor and cause the drive to misread information and not perform as instructed. Noise is a little thought, high impact problem that is relatively easy to minimize.

 

Cable selection is crucial.  Try to buy cable with the correct number of wires.  Use twisted pairs for the send and return of each circuit if possible.  Keep your cables as short as possible, and do not just coil up the extra cable and leave it in a cabinet.

 

Use shielded cabling always.  Just having a shield inside the cable is not enough; it needs to be properly grounded at either the motor or the drive but not both.  Shielded cabling can actually make your problem worse if you do not have a solid ground.

 

Keep feedback cables from looping around or running closely parallel to high voltage cables.  Maximizing distance between communication and high voltage cabling will minimize the impact of noise on your system.

 

Motors/Drives/Encoders are often misdiagnosed as bad when they are really just being affected by noise.  Minimizing noise will save you downtime and unnecessary repair costs.