Electric Motors in Dentistry

By: Steve Aucremann

On:


Electric Motors in Dentistry


In case you missed it, electric motors are rapidly replacing air driven handpieces in the dental industry. Although this has long been the standard in Europe we in the US have been slow to change. The primary advantage of the electric motor over air driven is the torque and as a bonus it is much quieter, easing the tension caused by whining air turbines. The down side is of course is the initial cost and the expense of repair.

 

In the world of electric motor handpieces there are 2 primary technologies, the brush motor (old technology, on the way out) and the Brushless motor most new systems are built with brushless motors they are more reliable and efficient as well as giving more accurate control over speed and torque.

 

 

Brush Motors


 

The brush motors operate off of DC current which is applied to carbon brushes that contact a circular commutator which has between 6 and 24 segments each opposing pair of contacts attaches to either end of a coil of wire on the rotor or armature. When the coil is energized it creates a magnetic field which pushes against the opposing force of the stator (usually a fixed magnet or magnets attached to the inside of the case of the motor) which causes the rotor to rotate to the next pair of contacts which energizes another coil and round and round it goes.

You will find brush motors in Lab handpieces, Operatory handpieces, even Implant handpieces. The primary problems you will find are:

  • Bad bearings (from contamination or age).
  • Worn brushes and/or commutator.
  • Open winding in armature.
  • Broken wire in the handpiece cord requiring re-termination or replacement.

 

 

Brushless Motors


Like the brush motor the brushless motor uses a coil of wire which is energized to create a magnetic field that pushes against an opposing field in a permanent magnet. However in the brushless motor the magnet is on the rotor and the coil is fixed. The pulses required to make the rotor go round and round are generated by a Microprocessor instead of brushes contacting a commutator. This is why we say that the brushless motor runs on a commutated signal not a DC voltage. It is also why a brushless motor needs at least 4 wires (conductors) and the brush motor only 2.  

 

As a result of the lack of brushes the brushless motor;

  • Is quieter and has less overall vibration.
  • Is cooler (most brush motors need a fan)
  • Can be designed to run faster and longer with a higher duty cycle (more time on less time off)
  • They require less maintenance. 

The down sides to the brushless motor are;

  • They must have a specific controller to be properly tested and sometimes the controller is the problem.
  • The magnet on the rotor can crack or break up (often if the handpiece is dropped)
  • Because these are often surgical handpieces they are autoclaved which degrades the windings and bearings over time.
  • Broken wires are often a problem probably because they require more conductors and are therefore smaller and more fragile.
  • The added layers of technology i.e. the microprocessor, the use of hall effect sensors and torque control makes problems harder to diagnose.

So what does it all mean


 

 

Really it just means we have to work together on these to get the best result for the customer. We have tried to distill this down to a few rules of thumb;

When you pick up an electric motor get as much information as you can, here are a few questions to ask.

  • Did the motor run or not?
  • Was it making noise or vibrating?
  • Do other motors work on that controller?
  • Did the motor go on and off if you twist the wire?
  • Is the motor getting hot?
  • Is the motor going slow with a jerking motion?

Try and determine if it is a brush motor (the motor runs on 2 wires is the easy way) and if the control works with other motors then just send the motor. If they do not have  an extra motor to run with the control then you may as well send in the control with the motor.

If you can put a straight nosecone with a burr in it and spin the motor you can learn a lot.

  • If it turns freely and the motor will not run when attached to the control, then putting bearings in it will not help.
  • If it won’t turn or feels like a box of rocks when you turn it, the rotor has most likely exploded and must be replaced,
  • If the motor runs but is loud, and the bearings feel rough when you turn it by hand, it can  likely be fixed with bearings
  • If the motor runs but jerks or stops, or causes an error when you twist the cord then it may only need a cord re-termination.

The following is a list of the systems we have in house to test handpieces with:

  • KAVO Electrotorque – will test KAVO 198 and 200 motors (brush motor)
  • KAVO Electrotorque plus – will test KAVO 700 and 701 brushless motors
  • KAVO Comfort drive  system – will test 200XDR motor
  • NSK – will test the  NSK NL400 brushless motor
  • Sirona Classic – will test the Sirona Classic brush motor
  • Sirona ISO will test Sirona E-type motor and the Classic brushless motor
  • ADEC W&H will test the EA40-LT EA51-LT and EA52-LED (but not feedback circuit)
  • Dentsply Aseptico will test most Dentsply or Aceptico brushless motors
  • W&H 3i  implant 4 pin will test most W&H 4 pin brushless motors
  • W&H Implant Med 5 pin will test most W&H 5 pin brushless motors
  • Stryker Command II – Stryker Command II brushless motors only
  • By Dental Hi tech Implant will test By Dental and Hi tech Implant brushless motor

 

 

 

 


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