1. ERT 457 – DESIGN OF AUTOMATION SYSTEMS
LECTURE 3.3
Electrical Actuation Systems
MUNIRA MOHAMED NAZARI
PPK BIOPROSES, UnIMAP

2. Course Outcome
CO 2
Ability to design (C5) automation system for agricultural and biological production system.

3. Introduction
Elements of electrical systems used in control systems as an actuator.
Switching devices
Control signal switches on or off some electrical device – motor
Mechanical switches – relays
Solid-state switches – diodes, thyristors and transistors.
Solenoid type devices
Current through solenoid is used to actuate a hydraulic /pneumatic flow.
Drive systems
Current through a motor is used to produce rotation – d.c and a.c motor.

4. Electrical Actuators, Drive Systems and Motion Control
Electrical motors DC
DC servo AC
Stepper motor
Drive system
Open-Loop positioning system
Close-Loop positioning system
Motion control
Motor driver
Numerical control (NC)

5. Electrical Motor
Electric motor converts electrical power into mechanical power.
Consists of two basic components - stator and rotor.
Stator – ring shaped stationery component
Rotor – cylindrical part that rotate inside the stator.
- assembled around shaft, supported by bearing.
Shaft can be coupled to machinery components such as
Gears
Pulley
Lead screw
Spindle

6. DC Motor Powered by constant current and voltage. Two types
Brushed DC Motor
Used commutator as rotary switching device.
Commutator rotate with the rotor and pick up current from set or carbon brushed.
Disadvantage – result in arcing, worn brushes and maintenance problem.
Brushless DC Motor
Used solid state circuit as switching device.
Advantage – reducing inertia of rotor assembly and higher speed operat
Two reason to used DC motor,
Convenience of using DC power – eg: car battery supply.
Torque speed relationships are attractive in many apllication compare to AC motor.

7. D.C. motor: (a) basics, (b) with two sets of poles
Brushed DC Motor
D.C. motor: (a) basics, (b) with two sets of poles

8. (a) Brushless permanent magnet motor, (b) transistor switching
DC Motor
Brushless DC Motor
(a) Brushless permanent magnet motor, (b) transistor switching

9. DC Servomotor Used feedback loop to achieve speed control.
The torque produced by motor and torque by the load must be balanced.
Operating point – amount of torque in steady state operation.

10. DC Servomotor Advantage of DC servo Calculation for DC servo operation
Ability to deliver a very high torque at starting velocity of zero.
Variable speed motor and bi-directional.
Calculation for DC servo operation
Torque , T = Kt i
Kt = torque constant for motor
i = current
Back e.m.f, vb = Kvω
Kv = back e.m.f constant for motor.
ω = angular velocity
Depending on the context, this could refer to several specific things. When electricity flows through a conductor (conductor A), it creates magnetic fields, which then create electric fields, around it and propogating away from it. If another conductor is nearby (conductor B), the electric field produced by the current flowing in conductor A will induce a current in conductor B. The current in conductor B will produce an electric field that is in the opposite direction of the electric field that produced the current in conductor B, which will attempt to cause current to flow in the opposite direction of current flow in conductor A. This is the "back EMF", or back electromagnetic force.

11. DC Servomotor DC motor with equivalent circuit
Starting current, i = V/R
Starting torque, T = Kt V/R
Current, i = V – Kvω R
Kv = back e.m.f constant for motor.
ω = angular velocity
R = resistance
V = voltage
Torque, T = Kt (V – Kvω)

12. Calculation for DC servo operation
A DC servomotor has a torque constant = N-m/A and a voltage constant 0.12 V/ (rad/sec). The armature resistance is 2.3 ohms. A terminal voltage of 30 V is used to operate the motor. Determine:
The starting torque generated by the motor just as the voltage is applied.
The maximum speed at a torque of zero.
Power delivered by the motor.
T = Nm

13. AC Motor
Can be classified into two groups, single phase and polyphase, with each group being further subdivided into induction and synchronous motors.
Single-phase motors tend to be use for low-power requirements while polyphase motors are used for higher powers.
Induction motors tend to be cheaper than synchronous motors and are thus very widely used.

14. AC Motor Single-phase squirrel-cage induction motor
Consist of a squirrel cage rotor – copper or aluminum bars that fit into slots in end rings to form complete electric circuits.

15. AC Motor Three-phase induction motor
Similar to the single-phase induction motor but has a stator with three windings located 120 degree apart, each winding being connected to one of the three lines of the supply.
The rotation of the magnetic field is much smoother than with the single-phase motor.
Has a great advantage over the single-phase motor of being self- starting.

16. AC Motor Synchronous motors
Have stators similar to induction motors but a rotor which is a permanent magnet.
The magnetic field produced by the stator rotates and so the magnet rotates with it.
With one pair of poles per phase of supply, the magnetic field rotates through 360° in one cycle of the supply and so the frequency of rotation with this arrangement is the same as the frequency supply.
Are used when a precise speed is required. They are not self- starting and some system has to be employed to start them.

17. Three-phase synchronous motor

18. AC Motor

19. AC Motor

20. AC Motor

21. AC Motor

22. Stepper Motor
Stepper motors use a magnetic field to move a rotor. Stepping can be done in full step, half step or other fractional step increments.
Voltage is applied to poles around the rotor. The voltage changes the polarity of each pole, and the resulting magnetic interaction between the poles and the rotor causes the rotor to move.
Stepper motors provide precise positioning and ease of use, especially in low acceleration or static load application.

23. Stepper Motor
Important performance specifications to consider when searching for stepper motors include:
Shaft speed
The no-load rotational speed of output shaft at rated terminal voltage. The terminal voltage is the design DC motor voltage.
The current per phase
The maximum rated current or winding for a stepper motor.
The continuous output power
The mechanical power provided by the motor output.
Static or holding torque
The maximum torque a motor can develop to hold its rotor in a stationary position.

24. Stepper Motor
Motor types for stepper motors can be permanent magnet, variable reluctance, or hybrid.
Permanent magnet (PM) motors
Use a permanent magnet on the rotor. Step angles range from 1.8 to 90 degree.
The most common and versatile stepper motor.

25. Permanent magnet two-phase stepper motor with 90° steps
Permanent magnet two-phase stepper motor with 90° steps. (a), (b), (c) and (d) show the positions of the magnet rotor as the coils are energized in different directions

26. Stepper Motor Variable reluctance (VR) motors
Have a free-moving rotor, no residual torque is produced due to lack of a permanent magnet.
The rotor is instead composed of a soft iron metal and also composed of its own very prominent poles, tending to stick out more than a rotor found on the PM version.
Step angles : 7.5 to 15 degree.

27. Variable reluctance stepper motor

28. Stepper Motor Hybrid motors
Consist of a heavily toothed PM rotor and toothed stators, plus prominent rotor poles like a VR rotor.
They are capable of very fine step angles: 0.9 to 1.8 degree and have a high-speed capability.
There is higher available torque than PM or VR stepper motors.
Most effective but most expensive stepper motor type.
Total number of steps/revolution = nm
n = motor phase on the stator
m = number of teeth on the rotor

29. Calculation for Stepper Motor Operation
A stepper motor has a step angle = 7.5°.
a) How many pulses are required for the motor to rotate through five complete revolutions?
b) What pulse frequency is required for the motor to rotate at a speed of 200 rev/min?
7.5° = 1 pulse
n pulses = 360° / 7.5°
= 48 pulses/rev
so, n pulses for 5 revolution,
= 48 pulses/rev x 5 rev
= 240 pulses.
b) fp = np Nm
= 48 pulse/rev x 200 rev/min
60 sec/min
= 160 pulses/sec
= 160 Hz

30. Stepper Motor Stepper motor specifications
Terms commonly used in specifying stepper motors:
Phase
The number of independent windings on the stator (eg: four-phase motor). The current required per phase and its resistance and inductance will be specified so that the controller switching output is specified.
Two-phase motor – light duty application, three-phase motor – variable reluctance stepper, four-phase and above motor – higher power application.
Step angle
The angle through which the rotor rotates for one switching change for the stator coils.
Holding torque
Maximum torque that can be applied to a powered motor without moving it from its rest position and causing spindle rotation.

31. Stepper Motor Pull-in torque Pull-out torque Pull-in rate
Maximum torque against which a motor will start, for a given pulse rate, and reach synchronism without losing a step.
Pull-out torque
Maximum torque that can be applied to a motor, running at a given stepping rate, without losing synchronism.
Pull-in rate
Maximum switching rate at which a loaded motor can start without losing a step.
Pull-out rate
Switching rate at which a loaded motor will remain in synchronism as the switching rate is reduced.
Slew range
The range of switching rate between pull-in and pull-out within which the motor runs in synchronism but cannot start up or reverse.

32. Stepper motor characteristics

33. Motor Selection
When selecting a motor for a particular application, factors that need to be consider are:
Inertia matching
Torque requirements
Power requirements

34. Motor Selection Inertia matching
For maximum power transfer, the moment inertia of the load should be similar to that of the motor.
When IM = IL, torque to obtain a given angular acceleration will be minimized.

35. Motor Selection P = Tfω + ILαω Power requirements
Total power (P) required is the sum of the power required to overcome friction and that needed to accelerate the load.
As power is the product of torque and angular speed, then the power required to overcome the frictional torque Tf is Tfω and that required to accelerate the load with angular acceleration α is (ILα)ω, where IL is the moment of inertia of the load.
P = Tfω + ILαω

36. Drive System Open Loop Control System Normally used stepper motor.
Operates without verifying that the actual position achieved in the move is the desired position.

37. Drive System Closed Loop Control System
Normally used servomotor (DC, AC & stepper motor).
Used feedback measurements to confirm that the final position of the worktable is the location specified in the program.

38. Motion Control
Motion control can refer to simple on-off control or sequencing of events, controlling the speed of a motor or other actuator, moving objects from one point to another, or precisely constraining the speed, acceleration, and position of a system throughout a move.
Motion controllers are components that range from ON/OFF devices with simple linear controllers to complex, user programmable modules that act as controllers within complex integrated multi-axis motion systems.

39. Motion Control
Motion control is an important part of robotics, CNC and machine tools.
Important performance specifications to consider when searching for motion controllers include:
Number of axes.
Update time.
D/A resolution.
Type of motion supported.

40. Motion Control The number of axes Update time D/A resolution
Usually correlates to number of motor outputs.
Update time
The time between position, speed or other feedback updates.
D/A resolution
Represent the “fineness” of the analog drive signal as converted from the digital command signal.
The type of motion supported
The ability for coordinated/interpolated motion of multiple axes. They include simple, linear and/or circular, complex ad user defined.

41. Numerical Control (NC)
Form of programmable automation in which the mechanical actions of a machine tool or other equipment are controlled by a program containing coded alphanumeric data.
The alphanumeric data represent relative positions between a workhead (cutting tool) and a workpart.
When the current job is completed, a new program can be entered for the next job.

42. Numerical Control (NC)
Applications of NC
Machine tool applications
Milling, drilling, grinding
Punch presses, thermal cutting machine
Other applications
Component insertion machines in electronics
Coordinate measuring machines
Drafting machine

43. Numerical Control (NC)
Basic components of an NC system
Program instructions
Part program in machining
Machine control unit
Controls the process
Processing equipment
Performs the process

44. Numerical Control (NC)
Motion control systems in NC
Point to point systems
System moves to a location and performs an operation at that location (eg: drilling).
Continuous path systems
System performs an operation during movement (eg: milling ).

45. Numerical Control (NC)
NC positioning system
Typical motor and leadscrew arrangement in an NC positioning system for one linear axis.
For x-y capability, the apparatus would be piggybacked on top of a second perpendicular axis.

46. Numerical Control (NC)
NC positioning system
Two types of NC positioning systems,
Open-loop
No feedback to verify that the actual position achieved is the desired position.
Closed-loop
Uses feedback measurements to confirm that the final position is the specified position.

47. Numerical Control (NC)
Analysis of Open Loop Positioning Systems
One axis of an NC positioning system is driven by a stepping motor. The motor is connected to a lead screw whose pitch is 4.0 mm, and the lead screw drives the table. Control resolution for the table is specified as mm. determine
a) the number of step angles required to achieve the specified control resolution
b) size of each step angle in the motor, and
c) linear travel rate of the motor at a pulse frequency of 200 pulses per second.

48. Numerical Control (NC)
Solution

49. Numerical Control (NC)
Analysis of Open Loop Positioning Systems
A DC servomotor is used to drive one of the table axes of an NC milling machine. The motor is coupled directly to the lead screw for the axis, and the lead screw pitch = 5mm. The optical encoder attached to the lead screw emits 500 pulses per revolution of the lead screw. The motor rotates at a normal speed of 300 rev.min. Determine
a) control resolution of the system, expressed in linear travel distance of the table axis.
b) frequency of the pulse train emitted by the optical encoder when the servomotor operates at full speed.
c) travel rate of the table at normal rpm of the motor.

50. Numerical Control (NC)
Solution