2. Chapter
Electromechanical Systems 6

3. Objectives
Discuss the five basic subsystems that are common to all automated robotic systems.
Describe mechanical systems as they relate to robotics.
Explain how sensing, timing, and control systems are used in the operation of robots.
Discuss rotary motion systems used for robotics.

4. Automated Systems and Subsystems
System is combination of components that work together
Electromechanical system uses mechanical motion to transfer power
Work occurs when energy is transformed into mechanical motion, heat, light, chemical action, or sound

5. Automated Systems and Subsystems
Subsystems are various components of a complete robot
Synthesized system is combination of subsystems

6. Automated Systems and Subsystems
Basic parts of automated system
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7. Energy Source Energy source provides system power
Alternating current power, electrons flow in one direction and then in opposite direction
Cycle is each repeated pattern of direction change
Single-phase is one alternating current
Three-phase is three alternating currents varying by 120°

8. Energy Source
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9. Energy Source Direct current, electrons flow in only one direction
Rectification converts alternating current to direct current

10. Transmission Path Transmission path is channel for transfer of energy
Load is part designed to produce work
May be alternate transmission paths in system

11. Control Control alters flow of power
Causes operational change in system
Control devices within transmission path
Anywhere between energy source and load device

12. Load Load is part designed to produce work
Electric motors, heating systems, lighting systems, alarms, and mechanical actuators
Largest portion of energy consumed by load device

13. Indicators
Indicator displays operating conditions at points throughout system
Digital meters, pressure gauges, tachometers, and thermometers

14. Mechanical Systems Mechanical motion transfers power to do work
Rotary, linear, and reciprocating motion
Electrical or fluid power energy source
Changing pressure, direction, force, and speed is control
Indicators measure physical quantities

15. Electrical Systems
Sensing
Timing
Control
Providing rotary motion

16. Sensing Systems
Sensing system signals response to particular form of energy
Light systems most common
Light pipes transfer light energy
Flexible, fiber-optic rods can extend long distances

17. Sensing Systems
Detector responds to source and outputs signal to control load device
Control in sensing system
Interrupting light beam between source and detector
Altering intensity, focus, shape, or wavelength

18. Sensing Systems
Counter on conveyor line
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19. Timing Systems Timing systems turn devices on or off
Delay timing provides lapse before load is energized
Interval timing uses specified time periods after load is energized
Cycle timing may include both interval and delay timing

20. Control Systems
Control systems continually make adjustments to alter machine operations
Control unit determines robot flexibility and efficiency

21. Control Systems Non-servo/open-loop control systems are most basic
Two open-loop variations:
Full control turns system off or on
Partial control alters system operations

22. Control Systems
Closed-loop system allows control unit and controlled element interaction
Feedback provides interaction information in closed-loop system
Activated by electrical, thermal, light, chemical, or mechanical energy

23. Control Systems Closed-loop system incorporates feedback
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24. Control Systems Closed-loop system with automatic correction control
Comparator compares feedback signal to reference signal or standard
Correction signal sent to control unit

25. Control Systems Comparator in closed-loop control system
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26. Control Systems Digital system components process numeric information
Instructions
Variations in pressure, temperature, or electric current

27. Rotary Motion Systems
Electric motor converts electrical energy to mechanical movement
Armature is electromagnet placed between permanent magnets
Poles of armature and magnets aligned

28. Rotary Motion Systems Poles repel and cause armature to rotate
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29. Rotary Motion Systems Torque is turning force Common parts of a motor:
Strength of magnetic fields and amount of current
Common parts of a motor:
Stator is stationary portion
Rotor is rotating component

30. Basic Parts of DC Motors
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31. DC Motors Commutator switches direction of current flow alternately
Produce one-directional direct current through armature windings
Brushes rub against commutator and allow current to flow through

32. DC Motors Field windings wrap around electromagnets
Create magnetic field of stator
Armature of DC motor rotates and generates its own voltage
Counter electromotive force (cemf)

33. DC Motors
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34. DC Motors Horsepower is measure of amount of work performed
Horsepower rating represents power of a motor
Percentage of speed regulation
Difference between no-load motor speed and rated full-load motor speed
Better speed regulation capabilities with lower values

35. Categories of DC Motors
Permanent-magnet
Series-wound
Shunt-wound
Compound-wound

36. DC Motors
Permanent-magnet dc motor power supply connected directly to conductors of rotor
Magnetic field produced by permanent magnets mounted in stator

37. DC Motors Permanent-magnet dc motor used for low-torque applications
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38. DC Motors
Series-wound dc motor armature and field circuits connected in series arrangement
One path for current to flow
Only dc motor that also operates using ac power

39. DC Motors
Series-wound dc motor produces high torque, but poor speed regulation
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40. DC Motors
Shunt-wound DC motor field windings connected in parallel with armature
Relatively high resistance
Small amount of current flows through
Field current changes result in corresponding changes in electromagnetic field flux

41. DC Motors
Shunt-wound dc motors have effective speed control characteristics
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42. DC Motors Compound-wound dc motor has two sets of field windings
One set in series with armature
One set in parallel with armature
High torque and good speed regulation

43. DC Motors
Compound-wound dc motor
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44. AC Motors Single-phase ac motors use single-phase ac power source
Three types: universal, induction, and synchronous

45. AC Motors Universal motors powered by either ac or dc source
Built like series-wound dc motor
Portable tools and small equipment

46. AC Motors
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47. AC Motors Single-phase induction motor has a solid rotor
Rotor set in motion by auxiliary method
Speed based on speed of rotating magnetic field and number of stator poles
Difference between synchronous speed (stator speed) and rotor speed is slip
More torque produced with greater slip

48. AC Motors
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49. AC Motors Three-phase ac motors use three-phase ac power source
Two basic types: induction and synchronous

50. AC Motors Three-phase induction motors have squirrel cage rotor
Voltage applied to stator
Good starting and running torque
Used in industrial applications

51. AC Motors
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52. AC Motors Three-phase synchronous motors deliver constant speed
Direct current applied to wound rotor produces electromagnetic field
Three-phase ac power applied to stator
External means needed to start
Zero slip at synchronous speed

53. Servo Systems
Servo systems respond to system feedback or error signals
Input is reference source
Load responds
Error detector receives data from input source and output device
Correction signal amplified and applied to actuator

54. Servo Systems Servo systems follow closed-loop control path
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55. Servo Systems
Servomotor produces controlled shaft displacements to achieve precise rotary motion
Two types: synchronous and stepping

56. Servo Systems
Adept

57. Servo Systems Synchronous motor comprised of rotor and stator assembly
No brushes, commutators, or slip rings
Requires carefully maintained air gap
Speed directly proportional to ac frequency and number of pairs of stator poles

58. Servo Systems Single-phase ac synchronous motor construction
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59. Servo Systems Two-phase synchronous motor with four poles per phase
Superior Electric Co.

60. Servo Systems
DC stepping motors change electrical pulses into rotary motion
Rotor has permanent magnet
More torque than synchronous servomotors
Stator coils wound using bifilar construction
Four-step switching sequence

61. Servo Systems

62. Rotary Electric Actuators
Rotary motion controls angular position of shaft
Transmit rotary motion without direct linkage
Computer signals applied to actuators and translated into rotary motion