1. Dept. of Electrical and Computer Engineering
ECE Mechatronics Assignment 1: Literature Survey on Sensors and Actuators Topic: DC Motors (Actuators)
Prepared by:
SIDDHARTH P. RAO
Dept. of Electrical and Computer Engineering
Utah State University
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2. Overview
“Actuators are basically the muscle behind a mechatronics system that accepts a control command (mostly in the form of an electrical signal) and produces a change in the physical system by generating force, motion, heat, flow, etc.”
Under the category of electromechanical actuators, a ‘motor’ is the most common one. It converts electrical energy to mechanical motion.
“Motors are the principal means of converting electrical energy into mechanical energy in industry.”
DC motors are those which operate on a DC voltage and varying the same can easily control their speed.

3. Types of DC Motors
Permanent Magnet type DC Motors: Contains no field coils.
 Further classified under this type as follows:
1). Conventional Permanent Magnet Motor  (“High efficiency, high peak power, and fast response”)
2). Moving Coil Permanent Magnet Motor.
 (“Higher efficiency and lower inductance than conventional DC motor.”)
3.) Torque Motor.
 (“Designed to run for a long periods in a stalled or a low rpm condition.”)

4. Types of DC Motors Wound Field type DC Motors:
 Further classified under this type as follows:
1). Series Wound DC Motor.
 (“High starting torque, high acceleration torque, high speed with light load”)
2). Shunt Wound DC Motor.
 (“Constant-speed application”)
3.) Compound Wound DC Motor.
 (“Low starting torque, good speed regulation Instability at heavy loads”)

5. Types of DC Motors
Electronic Commutation Type DC Motors (brushless motors):
 Fast response.
 High efficiency, often exceeding 75%
 Long life, high reliability, no maintenance needed.
 Low radio frequency interference and noise production.

6. Basic Working Principle
For any electric motor, its operation is based on the principle of simple electromagnetism.
Now, a current-carrying conductor generates a magnetic field.

7. Basic Working Principle
When this is then placed in an external magnetic field, it will experience a force proportional to the current in the conductor, and to the strength of the external magnetic field.
The internal configuration of a DC motor is designed to harness the magnetic interaction between a current-carrying conductor and an external magnetic field to generate rotational motion.

8. Basic Working Principle
The above figure shows a simple 2-pole DC electric motor (here red represents a magnet or winding with a "North" polarization, while green represents a magnet or winding with a "South" polarization).
Every DC motor has six basic parts namely: axle, rotor (i.e., armature), stator, commutator, field magnet(s) and brushes.

9. Basic Working Principle
In most common DC motors, the external magnetic field is produced by high strength permanent-magnets.
The ‘stator’ is a stationary part. This includes the motor casing as well as two or more permanent magnet pole pieces.

10. Basic Working Principle
The rotor (together with the axle and attached commutator) rotate with respect to the stator.
The rotor consists of windings (generally on a core), the windings being electrically connected to the commutator.

11. Basic Working Principle
The geometry of the brushes, commutator contacts, and rotor windings are such that when power is applied, the polarities of the energized winding and the stator magnet(s) are misaligned, and the rotor will rotate until it is almost aligned with the stator's field magnets.
As the rotor reaches alignment, the brushes move to the next commutator contacts, and energize the next winding.
In real life, though, DC motors will always have more than two poles (three is a very common number). In particular, this avoids "dead spots" in the commutator.
With the above example of two-pole motor, if the rotor is exactly at the middle of its rotation (perfectly aligned with the field magnets), it will get "stuck" there.

12. Basic Working Principle
The above figure shows a three-pole design of a DC motor.
We notice that one pole is fully energized at a time (but two others are "partially" energized).

13. Basic Working Principle
As each brush transitions from one commutator contact to the next, one coil's field will rapidly collapse, as the next coil's field will rapidly charge up (this occurs within few microseconds).

14. Basic Working Principle

15. DC Motor Equivalent Circuit

16. DC Motor Equivalent Circuit
The operation equations are as follows:
 Armature voltage equation:
 The induced voltage & motor speed Vs angular frequency:
Where,

17. DC Motor Equivalent Circuit
The operation equations are as follows:
 The combination of the equations result in:
 The current is calculated from this equation. The output
power is given by:
And the torque is given by:

18. Sample Configuration in Application
There are a number of high volume applications for DC motors that require precision control of the motor’s speed.
Phase locked loop techniques are well suited to provide this control by phase locking the motor to a stable and accurate reference frequency.
Thus, the small signal characteristics, and several large signal effects, of these loops have to be considered.
“PHASE LOCKING GIVES PRECISION SPEED CONTROL.”

19. Sample Configuration in Application
The precise control of motor speed is a critical function in today’s disc drives.
Other data storage equipment, including 9 track tape drives, precision recording equipment, and optical disc systems also require motor speed control.

20. Sample Configuration in Application
One of the best methods for achieving speed control of a motor is to employ a phase locked loop.
With a phase locked loop, a motor’s speed is controlled by forcing it to track a reference frequency.

21. Sample Configuration in Application
The reference input to the phase locked loop can be derived from a precision crystal controlled source, or any frequency source with the required stability and accuracy.
In above figure, a precision crystal oscillator’s frequency is digitally divided down to provide a fixed reference frequency.

22. Sample Configuration in Application
The motor speed is sensed by either a separate speed winding or, particularly in the case of the DC brushless motor, a Hall effect device.
The two signals, motor speed and reference frequency, are inputs to a phase detector.

23. Sample Configuration in Application
The detector output is a voltage signal that is a function of the phase error between the two inputs.
The transfer function of the phase detector, Kf, is expressed in volts/radian.
A 1/s multiplier accounts for the conversion of frequency to phase, since phase is the time integral of frequency.
Following the phase detector is the loop filter, which contains the required gain and filtering to set the loop’s overall bandwidth and meet the necessary stability criteria.

24. Sample Configuration in Application
The output of the loop filter is the control input to the motor drive.
Depending on the type of drive used, voltage or current, the driver will have respectively, a Vout/Vin transfer characteristic, or an Iout/Vin transconductance.
At first glance, it seems that the motor has simply replaced the VCO (voltage controlled oscillator), in the classic phase locked loop.
It is, in fact, a little more complicated. The mechanical and electrical time constants of the motor come into play, making the transfer function of the motor more than just a voltage-in, frequency-out block.

25. Major Specifications of DC Motors
Basically, specifications of DC motors depend mainly on the type of motor and the application where it is to be used.
Among the major performance specifications are following:
Shaft Speed: No-load rotational speed of output shaft at rated terminal voltage.
Terminal Voltage: Usually derived my the designer according to the application requirements.
Continuous Current: Maximum rated current that can be supplied to the motor windings without overheating.

26. Major Specifications of DC Motors
Continuous Torque: Output torque capability of the motor under constant running conditions.
Continuous Output Power: Mechanical power provided my the motor output.
Apart from the above listed specifications, the designer/user may have to consider the type of motor (PM, shunt wound, series wound, etc) and the type of commutation (brush / brushless).
Also, the type of gearing has to be considered depending on the type of application. Some types of gearing choices are : Spur, Planetary, Harmonic, Worm, Bevel, etc.
Finally, the type of “Shaft” is also to be decided. Some of the types are : In-line, offset/parallel, right angle, hollow, etc.

27. Application of DC Motors
DC Motors are used is a very large number of applications and its use varies depending on the type and the environment of the same.
Under the category of ‘Appliances’, Brushed DC motors are used in Coffee Grinders, Bread Makers, Can Openers, Ice Makers, Ice Cream Makers, Juicers, Vacuum Cleaners, Steam Cleaners, Polishers, Waxers, Blenders, Mixers, Food Processors, Electric Toothbrushes, Hair Clippers, Electric Razors.
Under the same category of ‘Appliances’, Brushless DC motors are used in Air Conditioner Compressors and Refrigerators.

28. Application of DC Motors
Under the category of ‘Automotives’, Brushed DC motors are used in Electric Windows, Electric Doors, Electric Hatches, Electric Sun Roofs, Electric Seats, Electric Retraceable Antenna, Windshield Wipers, Electric Starters, HVAC Fan and Electric Vehicles.
Under the same category of ‘Automotives’, Brushless DC motors are used in Electric Fuel Pump, Electric Oil Pump, Electric Radiator Fan, Electronic Power Steering (EPS), Anti-Lock Brake System (ABS), Electronic Throttle Control, HVAC Fan, Electric Vehicles.
Under the category of ‘Consumer applications’, Brushed DC motors are used in Moving Toys, Toy Robots, Radio Controlled Vehicles, Exercise Equipment, Computer PC Fans, Cordless Hand Tools.

29. Application of DC Motors
Under the same category of ‘Consumer applications’, Brushless DC motors are used in Radio Controlled Vehicles, Sewing Machines, Computer Hard Drives, Computer Tape Drives, Cordless Hand Tools, Camera Motor Drives, Camcorders, CD/DVD Equipment, Tape Decks and VCRs.
Under the same category of ‘Consumer applications’, 2-phase Brushless DC motors are used in Computer PC fans.
Finally, under the category of ‘Industrial applications’, Brushless DC motors are used in Large Movement Control/Hoist, Crane, Elevator and in Precision Movement Control: Printers, Robots, Milling; Medical Equipment; Servo Control.

30. Advantages of DC Motors
Wide speed range, 1000:1
Servo performance.
Positioning capabilities to within 1/4 of an encoder count.
Precise speed and torque control.
0.05 per cent speed regulation.
Less than 3% torque linearity of the full speed range.
100% torque at 0 rpm.

31. Advantages of DC Motors
Moderate PWM losses.
Sensorless operation.
Low cost (only in case of ‘brushless dc trapezoidal’ motors).

32. Limitations of DC Motors
‘Brushless DC Servo motors’ have High PWM losses.
High radial forces on motor.
Limited over-speed range.
Higher torque ripple.
In case of ‘Brushed DC motors’, due to wear and tear, the life of he motor is less and thus, more maintenance is required.
In some cases, the noise is more audible.
Not all DC motors are highly efficient.

33. Selection, Cost & Buying Info
Selection of DC motors completely depends on the type of applications in which it is being used. It can be a brushed DC motor, a brushless DC motor, etc.
Based on the type of application, DC motors range from as low as $5 to as high as over $4000 per unit.
There are many online stores from where DC motors can be purchased depending on the type of application. Some of the good e-stores are as follows:

34. References Motor Control Design Center
Motors and Electricity-today
DC motors : principle of solarbotics
Notes on gizmology
Design Notes on Precision Phase Locked Speed Control for DC Motors
Lecture notes from Arizona State University
‘The Mechatronics Handbook’ from EngnetBase.

35. Thank You…!