Step 15.7: Index the Belt
Contents
Background:
The Belt is modelled to move with constant velocity. We want it to index.
An Indexing Belt is one where, in one machine cycle:
| 1. | There is an Index-Period: The belt moves to a position during one phase of the machine cycle. |
| 2. | There is a Dwell-Period: The belt stops at that position for the remainder of the machine cycle. |
We must change the motion-values that we give to the kinematic-chains.
We connect new Function-Blocks to the input-connector of the Motion-Dimension FB to give a different motion to the Belt.
Function-Blocks for a Constant Velocity Belt
 Schematic of FBs of one Slider Set for belt moving at constant velocity. |
Schematic of the Function-Blocks for a Constant-Velocity Belt The image to the left is a schematic of how to connect the Function-Blocks to model the Path of the Constant Velocity Belt. The MMA motion value is the independent variable at the input of the separate X & Y Motion FBs. For each motion value at the input of a Motion FB, there is a specified motion value at the output. It does not matter how fast or slow the input changes (to change the speed of the Belt), the motion value at each output-connector is the same for each motion-value at an input-connector. The MMA increases continuously from 0 to 360, and again and again. The X & Y Motions were specified to give a constant velocity Belt. See Design the Motion for the Belt. |
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Function-Blocks for an Indexing Belt
 Schematic of one Slider Set for belt moving at constant velocity. |
Schematic of the Function-Blocks for an Indexing Belt We want the belt to index along the path, and stop at fixed positions during the dwell. To do this, replace the motion that is given to the input-connectors of the Motion FBs
Note: the MMA must still be at the input-connector to the Indexing Motion FB |
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This is an example 'Indexing Motion'. Segment 1: Y-axis : 0 - 360º | X-axis : 0º - 180º Segment 2: Y-axis (Dwell Segment) : 30º| X-axis : 180º - 360º. The image shows the position and acceleration graphs. |
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Question: Spot the problem? Answer: The output from the indexing motion changes from 0 – 360º in one machine cycle. Thus, the belt and pocket move from the start to the start position again in one machine cycle (0 – 360 of the MMA). We need to do two things:
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To index the Belt 12 times... To index the belt motion twelve times (12×) in one machine cycle (0 – 360 of the MMA):
Now, the motion-values at the output from the Gearing FB and input to the Motion FB are from 12×(0 ... 360) = (0 ... 4320º) as the MMA changes from 0 to 360. |
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Edit the Index motion the Belt 30º... To index the Belt 30º, edit the Motion in MotionDesigner. The Index motion to the left: Segment 1: Y-axis : 0 - 30º | X-axis : 0º - 180º Segment 2: Y-axis (Dwell Segment) : 30º| X-axis : 180º - 360º. Input to Motion FB is 0 ... 4320, : Output from Motion FB is 12× Index motions in 0 ... 360 (MMA) |
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The Graph to the left shows the output from the Motion FB as a function of the input, to the Motion FB: 0 – 4320º Note: To see the input to the Motion FB, (0 to 4320), connect a wire from the Gearing FB as the X-axis of the Graph FB Question: Spot the Problem? Answer: The output from the Motion FB does one index to 30º each 0 - 360 at its input, but resets to 0º, and does this motion again and again, 12×. |
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We will use the Accumulate Output radio-button in the Motion FB dialog-box.
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This graph now shows:
The output (Y-axis) from the Motion FB increases from 0 – 30º for the first 180º of the of the, and stays at 30º between 180 – 360º. Then the output (Y-axis)t increases to 60º for from 360º to 540º There are 12 indexes in one cycle of the MMA. Each index increases the position of the output by 30º. This is the motion that we want for the pocket and chain-link The pocket and chain-link will move 12 times, in one cycle of the MMA. |
