﻿ Tutorial 1: Indexing Motion

# Motion Design: Tutorial 1: Indexing Motion

## Indexing Motion

This tutorial designs an indexing motion.

After this tutorial you should be able to:

 • delete segments
 • make sure the Motion-Width is 360­º
 • change the motion-law of a segment
 • edit the X-axis value of a Blend-Point
 • edit the Y-axis Position of a Blend-Point

#### Terminology and Index Motions

Index Motions usually have two segments:

SEGMENT 1: Index Segment.

We must specify its:

 • Index-Period:  the rotational angle of the input-shaft (X-axis) as the output shaft also rotates
 • Index-Angle: the rotational angle of the output-shaft (Y-axis) during the Index-Period.
 • Motion-Law: the mathematical function for the rotational angle of the output-shaft as a function of the rotational angle of the input-shaft .

SEGMENT 2: Dwell Segment.

We must specify its:

 • Dwell-Period†: the number-of-degrees the input-shaft rotates during the dwell segment.
 • Dwell Period = 360 - Index-Period

Note:

When you design a 3D-Cam, it is frequently better to use three segments : Dwell–Index –Dwell,  to be symmetrical at 180° (360/2).

Period = Time-Period, Duration, or Interval.

Video : Motion Tutorial 1: Design an Indexing Motion

 Motion Tutorial 1: Design an Indexing Motion

 Starting from the Default Motion
 Default Motion: Number of Segments = 4 Motion-Width = 360º Motion Rise = 90º Motion-Laws = All 4 are Flexible Polynomial Motion 'type' = Rise-Dwell-Return-Dwell Notes: The X-axis is the horizontal axis. You can see its units are 'degrees'. The X-axis usually represents one machine shaft rotation rotation, 360º. The Position, Velocity, Acceleration and Jerk graphs are exactly above each other, and are the same motion, but at different motion-derivatives. The X-axis is the same for all of the motion graphs. Segment Names Selected-Segment - is the RED segment Previous-Segment - is to the left of the Selected-Segment. Next-Segment - is to the right of the Selected-Segment.
 Edit the Y-axis units

If the Y-axis units are not 'degrees' then, to make them 'degrees':

 1 Click the Edit toolbar > Active Motion-Settings
 2 Click the Active Motion-Settings > Motion tab > Motion Units separator : Y-axis Position units
 3 Select 'degree' in the drop-down box.
 Delete Two Segments

Indexing motions usually have 2 segments. Thus, we must delete two segments from the default motion.

Before we can delete a segment, we must make it the Selected-Segment

 1 Click in the motion-graph area above or below the last segment

The RED Selected-Segment is the last segment.

To delete the RED Selected-Segment

 2 Click the Blend-Point & Segment Editor toolbar > Delete Segment

See toolbar above

 • The last segment stretches.
 • The total does not change; it remains at 360º.
 • The first segment becomes the RED Selected-Segment.

We want to delete the last segment.

 3 Do again Steps 1 and 2

That is: Click the last segment, and then

Blend-Point-Segment toolbar >Delete Segment,

The motion is to the left.

 • There are two segments.

Terminology:

 • Period (time period): also applies to a number-of-degrees along the X-axis.
 • Index-Period: The number-of-degrees along the X-axis during which the Y-axis is in motion.
 • Dwell-Period: The number-of-degrees along the X-axis during which the Y-axis is not in motion.
 • Index-Angle: The range of the output motion - in Y-axis units.
 Edit the Motion-Law and Blend-Points

The motion we have:

 • Segment 1: X-axis Segment-Width = 90º ( the Index-Period)
 • Segment 2: X-axis Segment-Width = 270º (the Dwell-Period)

The Motion-Width 90 + 270 = 360º

The motion Y-axis

 • Segment 1: Y-axis 0-90º (called the Index-Angle)

The motion we want:

 • Segment 1: X-axis Segment-Width = 120º ( the Index-Period)
 • Segment 2: X-axis Segment-Width = 240º (the Dwell-Period)

The Motion-Width 120 + 240 = 360º (as before)

The motion Y-axis

 • Segment 1: Y-axis 0-120º (called the Index-Angle).

We must edit the Segment-Width of the segments, but we must not change Motion-Width. We can:

 • Use the Blend-Point Editor to the move the Blend-Point to the right.
 • Use the Segment-Editor to make the first segment longer and then make the last segment shorter.

The best tool to edit the Segment-Width, when we do not want to edit the Motion-Width, is the Blend-Point Editor.

 STEP 1. Open the Blend-Point Editor

Click: Blend-Point and Segment toolbar > Open Blend-Point Editor.

Blend-Point Editor button

 STEP 2. Make sure the active Blend-Point is #2
 1 Use the Previous / Next buttons to move the active Blend-Point to #2

You can see the X-axis position is at 90º

Note: You can also make sure the second segment is the RED Selected-Segment before you open the Blend-Point Editor.

The Next / Previous buttons are important when you want to edit (or find) a 'very short' segment in the motion that you cannot click (or see) in the motion graph.

 STEP 3. Edit the X-axis value

Note: The Blend-Point Editor can only edit the the motion-values at the left (the start) of the RED Selected-Segment.

We can use the spin-box tool to edit the X-axis value of the Blend-Point.

 1 Click the bottom arrow-buttons in the spin-box control to increase the Spin-Increment from 1 to 10.
 2 Click the top arrow-buttons in the spin-box control to increase X-axis motion-value from 90º to 120º.

Or:

 1 Use your keyboard to enter a value in the X-axis box (enter 120)
 2 Use the 'Enter' key on your keyboard to update to the new value (120)

General Reminder:

The Blend-Point Editor edits the active Blend-Point.

The active Blend-Point is at the left of the RED Selected-Segment.

As you edit the X-axis value of the active Blend-Point, the duration (period) of the Previous- Segment and the RED Selected-Segment change at the same time.

The Motion-Width does not change.

 STEP 4. Change the Motion-Law of the last segment (#2) to a Dwell

The default motion uses Flexible-Polynomial Motion-Laws for each segment.

 1 Click the last segment so that it becomes the RED Selected-Segment
 2 Click the Motion-Law Selector
 3 Select Dwell to change it from a Flexible-Polynomial to a Dwell motion-law
 STEP 5. Change the Motion-Law of the first segment (#1) to a Modified-Sinusoid
 1 Click the first segment so that it becomes the RED Selected-Segment
 2 Click the Motion-Law Selector again
 3 Select Modified-Sinusoid to change the motion-law from a Flexible-Polynomial to a Modified-Sinusoid motion-law.

VERY IMPORTANT: Click in the graph area (not on the segment) to remove the 'focus' from the Motion-Law selector. Otherwise, if you use your scroll mouse button, you will scroll through the motions! Not good!

 STEP 6. Edit the Index-Angle (Y-axis-Values)

If necessary, open the Blend-Point Editor again - see STEP 1

Make sure the second segment is the RED Selected-Segment - see STEP 2

In the Y-axis values separator, edit the 'End-Position' of the Blend-Point. We want to increase it from 90 to 120º

 1 Click the spin-box of the End-Position - see image to the left - to increase the Y-axis value of the Blend-Point from 90 to 120º

The graph auto-scales. Thus, look at the Y-axis scale of the Position graph (left of motion graph) to see the change to the motion.

Question: What if you do not change the 'Motion-Law' of the second segment to a Dwell?

Answer: The second Blend-Point moves up or down along the Y-axis, but the last Blend-Point does not move.

You will need to edit the End-Position of the last segment. To do this, you must first make Blend-Point #1 the active Blend-Point.

To edit the End-Position of the motion, you must click the FIRST SEGMENT.

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd