1. PROGRAMMABLE AUTOMATION
Chapter 2
PROGRAMMABLE AUTOMATION
NC/CNC/DNC

2. Conventional Manufacturing Manufacturing Support System Facilities
Automated Manufacturing
Fixed Automation
Programmable Automation
Flexible Automation

3. Conventional Manufacturing Manufacturing Support System Facilities
Automated Manufacturing
Fixed Automation
Programmable Automation
Flexible Automation

4. Programmable Automation
CAD
CAE
CAPP
CAM
CAQC: Computer Aided Quality Check

5. Automated Manufacturing
Programmable Automation
CAD
CAE
CAPP
CAM
CAQC: Computer Aided Quality Check

6. CAM
CAM
CAM
NC Machines
CNC Machines
DNC Machines

7. CAM NC Machines CNC Machines DNC Machines Hardware
Machine Control Unit (MCU)
The Method of Program execution
CNC Machines
DNC Machines

8. CAM NC Machines CNC Machines DNC Machines Hardware
Machine Control Unit (MCU)
The Method of Program execution
CNC Machines
Functions of MCU in CNC
CNC Programming with Fanuc Controller (G-Code & M-Code)
DNC Machines

9. CAM NC Machines CNC Machines DNC Machines Hardware
Machine Control Unit (MCU)
The Method of Program execution
CNC Machines
Functions of MCU in CNC
CNC Programming with Fanuc Controller (G-Code & M-Code)
DNC Machines
Working Principle

10. Comparison Comparison of Conventional Machines with CNC
Comparison of NC with CNC Machine

11. 1st CNC by MIT

12. CNC Programming Axis Designation Tool Movements Reference Points
Coding system
CNC Syntax
Programming Mode
Tool Offsets
G-Codes & M-Codes in Detail (With Program)

13. At 1970-1972 first Computer Numeric Control machines were developed.
HISTORY
US Air Force commissioned MIT to develop the first "numerically controlled" machine in It was demonstrated in 1952.
At first Computer Numeric Control machines were developed.
Today, computer numerical control (CNC) machines are found almost everywhere, from small job shops in rural communities to companies in large urban areas.
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14. NC Machines
Numerical Control (NC)is a 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 & a workpart.
NC in Machine tool applications: drilling, milling
NC in non Machining application: assembly, drafting, inspection

15. NC SYSTEM ELEMENTS
A typical NC system consists of the following elements
Program of Instruction (part program)
Machine control unit
Processing equipment (Machine tool & cutting tool)
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16. Program of Instruction Machine Control Unit (MCU)
Basic Components of NC System
Program of Instruction
Machine
Control
Unit (MCU)
Processing Equipment

17. NC Machine System

18. PART PROGRAM
A part program is a series of coded instructions required to produce a part. It controls the movement of the machine tool and the on/off control of auxiliary functions such as spindle rotation and coolant. The coded instructions are composed of letters, numbers and symbols and are arranged in a format of functional blocks as in the following example
N10 G01 X5.0 Y2.5 F15.0    |       |       |         |        |    |       |       |         |       Feed rate (15 in/min)    |       |       |        Y-coordinate (2.5")    |       |      X-coordinate (5.0")    |      Linear interpolation mode   Sequence number
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19. Program is coded on a suitable medium
In case of NC machines program was coded on 1-inch wide punched tape.
Tape may be paper, plastic or magnetic tape.
Program is read by a suitable input device.

20. PROGRAM INPUT DEVICE
The program input device is the mechanism for part programs to be entered into the NC control. The most commonly used program input device is punched tape reader.
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21. Punch Card

23. Punched Tape Sequence of processing steps is called a part program.
The medium to write a part program in NC machine was a 1-inch punched tape.
NC Machine coding system uses alphabetical characters ,numerical and other special symbols in part program.

25. There are 2 standard coding system used in NC.
The Electronic Industry Association (EIA)
EIA RS-244 B
International Standard Organization (ISO)
ASCII

29. Program Writing
Program Writing
Parity checking

30. N10 G01 X5.0 Y2.5 F15.0 N

31. N10 G01 X5.0 Y2.5 F15.0 N 1

32. N10 G01 X5.0 Y2.5 F15.0 N 1

33. N10 G01 X5.0 Y2.5 F15.0 N 1
Space

34. N10 G01 X5.0 Y2.5 F15.0 N 1
Space G

35. N10 G01 X5.0 Y2.5 F15.0 N 1
Space G

36. N10 G01 X5.0 Y2.5 F15.0 N 1
Space G 1

37. N10 G01 X5.0 Y2.5 F15.0 N 1
Space G 1
Space

38. Parity 5

39. Parity 5

42. Punched Tape Reader

45. Machine Tool
In NC Machine tools each axis of motion is equipped with a separate driving device which replaces the handwheel of the conventional machine.
The driving device may be a dc servo motor, a hydraulic actuator or a stepper motor.
Selection depends on accuracy & power requirement.
Motion to tool or worktable is transmitted by gears & ball screws.
Machine tool drives are also fitted with feedback devices (Closed loop control).

46. MACHINE CONTROL UNIT
The machine control unit (MCU) is the heart of a NC system. It is used to perform the following functions:
Read coded instructions, one by one
Decode coded instructions
Provide decoded information to the control loops of the machine axes of motion.
Control machine tool operation.
Advance tape each time the previous instructions were fulfilled.
Axis of a machine tool is defined as a path along which relative motion between the cutting tool and the workpiece occurs and a machine can have more than one axis.

47. The MCU includes
the Data Processing Unit (DPU) and
the Control Loop Unit (CLU)

48. MCU
DPU reads the part program, decodes it, processes the information and passes data to the CLU
Such data contains the new required position of each axis, its direction of motion and velocity, and auxiliary control signals (like coolant on/off)
CLU convert the information to control signals and drives the mechanism (Motor & Ball screw), receives feedback (about position and velocity) for each axis and instructs DPU to read new instructions

49. DPU includes at least Input device, Punched tape reader
Reading circuits & parity checking logic
Decoding circuits for distributing data among the controlled axes.
Interpolators, which supplies velocity commands between the successive points taken from the drawing.

50. CLU consists of the following circuits:
Position control loops for all the axes of motion
Velocity control loops
Deceleration & backlash take-up circuits
Auxiliary function control, such as coolant on & off, spindle on & off

51. DRIVE SYSTEM
A drive system consists of amplifier circuits, stepping motors or servomotors and ball lead-screws. The MCU feeds control signals (position and speed) of each axis to the amplifier circuits. The control signals are augmented to actuate stepping motors which in turn rotate the ball lead-screws to position the machine table.
2004

52. Each Slide is also fitted with feedback transducer, which continuously monitors the slide position and compares with the programmed position as well as feedrate.
2 types of feedback are taken, one for position & one for speed.

53. Drive Motors
Servo Motors
Stepper Motors
Hydraulic Motors

54. Servo Motors
A servo motor can be either DC or AC, and is usually comprised of the drive section and the resolver/encoder.
Servo Motors are variable speed motors that rotates in response to the applied voltage.
DC Servo motors are controlled by varying the voltage magnitude.
AC Servo Motors are Controlled by varying the Voltage frequency.

55. A servo motor is much smoother in motion than a comparable stepper, and will have a much higher resolution for position control. The servo family is further divided into AC and DC types. An AC servo had the advantage of being able to handle much higher current surges than a DC, as the DC has brushes, which are the limiting factor in this case.

56. AC Servo is Stronger than DC servo
The trend for manufacturers of “serious” CNC machinery is to use AC servos. “Entry level” machines may have DC servos, or even steppers.

57. STEPPING MOTORS
A stepping motor provides open-loop, digital control of the position of a workpiece in a numerical control machine. The drive unit receives a direction input (cw or ccw) and pulse inputs. For each pulse it receives, the drive unit manipulates the motor voltage and current, causing the motor shaft to rotate by fixed angle (one step). The lead screw converts the rotary motion of the motor shaft into linear motion of the workpiece .
2004

58. STEPPING MOTORS
2004

59. A stepper motor is wound in such a way that the rotation has a certain number of discrete "steps".
The number of steps per revolution is rather high, around two hundred or so, and varies by model and manufacturer. What this means is that the motor has effectively a resolution (smallest controlled movement) equal to the number of steps for that motor.

60. Stepper systems are often “open loop” which means that the controller only tells the motors how many steps to move and how fast to move, but does not have any way of knowing where they actually are. This can lead to errors, should a situation arise where the motors are unable to comply with the commanded move.

61. This can be very obvious, where the motion stops and it sounds like you stripped a gear, or subtle, where the motor only misses a “few” steps. The result is the same - the controller thinks you are at X25.5, Y15.5 and in reality you might be at X25.3, Y This can lead to a cumulative error, which may in turn lead to crashes, not to mention out of spec parts.

62. Hydraulic Motor
Variable Speed Motors

63. RECIRCULATING BALL SCREWS
Transform rotational motion of the motor into translational motion of the nut attached to the machine table.
2004

65. RECIRCULATING BALL SCREWS
Accuracy of NC/CNC machines depends on their rigid construction, care in manufacturing, and the use of ball screws to almost eliminate slop in the screws used to move portions of the machine.
2004

66. 2004

67. TYPES of NC CONTROL SYSTEMS
Open-loop control
Closed-loop control
2004

68. Open Loop Control System
In open-loop control system step motors are used
Step motors are driven by electric pulses
Every pulse rotates the motor spindle through a certain amount
By counting the pulses, the amount of motion can be controlled
No feedback signal for error correction
Lower positioning accuracy
Less costly

69. CLOSED-LOOP CONTROL SYSTEMS
In closed-loop control systems DC or AC motors are used
Position transducers are used to generate position feedback signals for error correction
Better accuracy can be achieved
More expensive
Suitable for large size machine tools
2004

70. Feed back
An integral feedback device (encoder and tachometer) are either incorporated within the servo motor or are remotely mounted, often on the load itself. These provide the servo motor's position and velocity feedback that the controller compares to its programmed motion profile and uses to alter its velocity signal.

71. Optical Encoder
Stepper Motors are provided with encoders.

72. Closes loop system Optical Encoder Lead screw Gear box (rge)
MCU
DAC
Servo Motor
Feed back signal

73. Precision in NC Positioning
Precision in NC Machine defined as
Control resolution
Accuracy
Repeatability

74. Control Resolution
Is the distance between 2 adjacent addressable points in the axis movement.
Depends on (a) The electromechanical components of the positioning system
(b) Number of bits used by the controller to define the axis coordinate location
CR=Max{CR1, CR2}

75. Addressable Points
Linear Axis
Control Resolution = CR

76. Accuracy Accuracy is effected by mechanical errors.
Accuracy means how exactly the position specified in the part program is achieved .
Accuracy in the worst case: desired target point lies in the middle of 2 addressable points.
This gives maximum possible positioning error.
Accuracy= CR/2 + 3σ

77. Repeatability
Repeatability= ± 3σ

78. Addressable Points
Distribution of
Mechanical Errors
Repeatability =±3 σ
Linear Axis
Control Resolution = CR

79. Addressable Points
Distribution of
Mechanical Errors
Desired Position
Accuracy = CR/2 + 3σ
Repeatability =±3 σ
Linear Axis
Control Resolution = CR