7) Encoders

Question 1

What is the purpose of a Displacement transducer?

Answer 1

Fixed along the 3 axis of the CMM. Determines position of touch trigger probe.

Question 2

What are examples of displacement transducers?

Answer 2

• Optical scales
  
  • Rotary encoders
  • Inductosyns
  • Magnetic scales
    
    • Laser interferometers

Question 3

What is the name for the laser displacement transducer?

Answer 3

Laser interferometers:

- Best way to measure linear movement

Question 4

What is the ideal criteria for a measurement?

Answer 4

• A Fixed reference reflector
• A Moving measurement reflector
• A Measurement of the environment

Question 5

Describe the Moire effect:

Answer 5

• Used in optical encoders.
• 2 very fine gratings. 1 fixed 1 moving.
• Angle of gratings affects the sensitivity

Question 6

What is the equation to calculate the separation of the moire fringes?

Answer 6

D = separation of moire fringes (vertical)
d = grating interval (horizontal distance between fringes)
0 = angle between gratings

D = d/0

Question 7

How is the extent of grating movement measured?

Answer 7

Detector used to measure extent of movement (but not direction)

2 detectors are used.

Question 8

How many counts are taken per cycle when measuring?

Answer 8

4 counts per cycle to measure.

Question 9

Which materials are used for the two methods of illuminating the gratings?

Answer 9

Materials: glass or stainless steel

Transmission or reflection methods available.

Transmitted (glass materials)

Reflected (steel)

Question 10

What Is the accuracy of the transducer mainly determined by?

Answer 10

Line placement accuracy of the grating.