Design Considerations

Power supply DC Battery supply possible
Driver electronics need No
Speed accuracy Low Effected by load torque
Manufacture tol +-10% of no load speed
Speed control Voltage Open loop or closed loop speed control Closed loop - high accuracy, but sensor need
Position control High effort Closed loop position control and sensor need
Overloadablity / load inertia High High start torque or peak load torque
Able to accelerate high load inertia
Lifetime Low 300...2000h (limited by wear of brushes) Depend on speed, current and brush config
Speed range [rpm] 1000...25000 No load speed
Efficiency 60...80% At operating point of max. efficiency
Power vs. size High
Winding thermal protection Need If overload (mechan.blocking) not excluded - Current limitation or thermal contacts
Load sensing Easy Current rises with load
Stalling permissible No No or only short time (winding overheat)
Electromag.interference EMI Critical Suppression means (capacitors / varistors)
Braking/Holding torque Low Detent torque
Braking improvable by winding short circuit
Max.output power from JE [W]
Linear motors from JE No
 

Encoder Motors

Encoders (Sensors) can be implemented inside the motor or mounted to motor rearside.

They are needed for a precise speed control or angular position control. Typical application: Printers and scanners.

There are different options:
  • Optical encoders
  • Hall-effect magnetic sensors
  • Resolvers

Johnson Electric offers a range of several optical encoders.

Basic principle: A slotted wheel or a black/transparent strip photo print is rotating with the motor shaft. A photo sensor provides a sine wave or pulse pattern that follows the speed of the motor.

Output signal can be analog (0...3.3Vac) or digital (0...3.3 Vdc or 0...5Vdc).

One signal or two signals phase shifted 90° (enabling detection of direction of rotation ; allows 4x resolution)

Several options for resolution. Terminology: CPR (Counts Per Revolution) and LPI (Lines Per Inch).

  

Example:
 
HC385MG with slotted encoder wheel
(CPR = 48 ; one signal, sine wave 0...3.3Vac)
 
NF123G with fotoprint wheel
(CPR= 32 ; two signals, sine wave 0....3Vac)