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page 672

We have a suction cup gripper with two 5”diameter cups that is to be used to lift 1/4” steel plates cut to 2’ by 3’. How much vacuum pressure must be applied to just hold the plates? Suggest a realistic value.

 

 

 

 

 

lb

1

× 24( in) × 36( in)

= 60.48( lb)

w = 0.28

------

--

in

3

4( in)

 

 

 

 

 

 

 

 

 

 

 

 

 

A =

2

 

 

 

5 2

 

 

2

 

 

2

 

 

 

 

 

 

 

π

--

 

 

= 2[ 19.63( in

) ] = 39.26( in )

 

 

 

 

 

2

 

 

 

 

 

 

 

Minimum to hold plate

 

w

 

 

60.48( lb)

 

1.54( psi)

 

P =

---

=

-------------------------

=

 

 

A

39.26( in2)

 

 

 

 

 

 

 

 

 

 

Assume low moving speed for robot, use factor of safety = 2.0

PS = 2.0 × P = 3.08( psi)

Note: this is much less than atmospheric pressure (15 psi), therefore it is realistic.

Advantages,

-requires only one surface of a part to grasp

-a uniform pressure can be distributed over some area, instead of concentrated on a point

-the gripper is light weight

-many different types of materials can be used

Disadvantages,

-the maximum force is limited by the size of the suction cups

-positioning may be somewhat inaccurate

-time may be needed for the vacuum in the cup to build up

39.4.3 Magnetic Grippers

Can be used with ferrous materials

Electromagnets,

-easy to control, requires a power supply, and a controller

-polarity can be reversed on the magnet when it is put down to reverse residual magne-

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