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Machine Tool Model

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					Machine Tool Model
Building on the earlier rotary table tutorial, this model adds the feature of a
simulated drilling or machine tooling operation. The purpose of this tutorial is to
model a machine that might be used in a factory setting, giving teachers and
students exposure to models that they can build and improve upon for the
integration unit in Computer Integrated Manufacturing.

The parts used in this construction are only suggestions. Make changes or
adaptations with the parts that you have available.

Project Construction
This model is based on a motor driven rotary table (with two divisions, though
you could certainly add more if you wish), and a tower with a motor driven
simulation tool. The table is only going to move in one direction, stopping and
starting points controlled by logic switches. When the rotary table has stopped
and is in position, the tower motor will lower and then return to its “home” position
at the top of the tower.

You will need two motors, and three switches for this project.




   Figure 1 Overview of the whole project
Figure 2 Close-up of motor and drive gear




Figure 3 Notice the upper and lower limit switches




Figure 4 Another look from the front
   Figure 5 Side view of tower

Wiring
In this example:

M1 is connected to the motor on the tower. M2 is connected to the motor driving
the rotary table.

The switch on the table is connected to I1. The switch at the top of the tower is
connected to I4, and the switch at the bottom of the tower is connected to I3.

Program Control.
Open RoboPro.

Start a new project and call it Machine Tool. Save it to a folder as directed by
your teacher.

Go to Main Toolbar and call up the Interface Test box.
   Figure 6 Interface Test dialog box
Click each switch in turn and make sure that the state changes from 0 to 1. (Here
the switches are wired as open, meaning “not engaged” or “not in contact.” When
the switch is depressed, the state changes to a 1 and a checkmark appears.)

What direction (clockwise or counter clockwise) moves M1 up the tower?
RECORD that information.

Check the direction that moves the rotary table, clockwise vs. counter clockwise.
Record that information.

In the model from the example, counterclockwise on motor 1 (the tower) brings it
DOWN. Clockwise on the rotary table, rotates the table clockwise. To change the
direction of the motor movement, change the wire positions.

While you using the Interface Test tool, be sure to check every input and output.
Be sure that the switches will change states (low to high) when engaged by
another piece. Now is the time to fine-tune your hardware design to avoid
collisions and crashes of parts plowing into one another.

The Program
The first section of the program will be designed to be sure that before the rotary
table moves, the machine tool is up and out of the way – this is for “safety”
reasons. Safety is a programmer’s first concern.

The first motor command of the program will make it move clockwise and stop
moving when it engages (changes the state of) switch E4. An edge trigger could
be used to monitor the states of E4 or E3; however, a factor of safety will be
lost... namely, what happens if the switch is already at the state reading a 1 since
the tool is already in position. Edges only check CHANGES.




   Figure 7 First part of the program, moving the tool up and out of the way


Once the tool is up and out of the way, the rotary table should turn on, and move
into position so that whatever part is on the table can be “operated” on.

A small but important problem is encountered. The switch doesn’t
instantaneously change its state from a 0 to a 1 or visa versa. In this application,
the motor needs to run an additional amount of time to move the piece off the
switch. So, before turning off the rotary motor, a wait command is needed. In this
example, a wait of .1 seconds worked. Experiment with different times to see
what works best to JUST BARELY change the state of the switch back to a 0
before the motor shuts off.
   Figure 8 Second part of the program, moving the table around
The third part of the program involves bringing the tool down until it hits its safety
switch (E3) and stops.




   Figure 9 Moving the tool down until it reaches its limit switch
The last part of the program involves repeating the whole process, which is easily
accomplished with a repeat.
   Figure 10 the whole program


Conclusions

1. This program simulates a machine tool. Suppose you want it to simulate a spot
welder. What could you change to make it seem more realistic?

2. What is the purpose of the time delay? What would happen if it weren’t there?

Problems
1. Change the program so that there is ample time to load and unload the rotary
table with parts.

2. Interface this setup with the conveyer belt program so they all work off signals
from each

				
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posted:4/16/2011
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