MechDesigner Reference & User Interface > Dialogs > Dialog: Function-Block: Point-Cloud

Point-Cloud FB

Do two(2) steps in the Point Cloud dialog:

STEP 1: Import-data ( the Point-Cloud, TXT file-type).

Use the

Frequently, the Point-Cloud are coordinates of a cam-profile, which are measured with a Coordinate Measurement Machine (CMM).

It is possible to use numerical techniques to calculate the motion-derivatives from the Point-Cloud.

STEP 2: Fit-a-Curve to the data

Use the Point-Cloud dialog to fit a Curve to the Point-Cloud.

The Curve is a continuous-function that we symbolically differentiate for you to calculate the motion-derivatives.

How to open the Point-Cloud dialog

Open the Point-Cloud dialog:

1.Double-click a Point-Cloud FB in the graphic-area

...see How to open a dialog

The Point-Cloud dialog is now open.

Point-Cloud dialog

There are two tabs:

STEP 1: Import Data

STEP 2: Fit Curve to Data

STEP 1: Import Data

Do A, B, and C.

Import and Browse buttons

Example File Format

A. Browse...

Click the Browse... button to select the data-file.

The data-file must by an ASCII, or TXT file-type.

The file-name shows in the Data-File (read-only) box. A preview of the data-file is in the box below.

B. Edit File-Format

Header text in the file is not imported.

The data should be rows of data-points - see Data-Points below

You can remove extra data from columns/rows with the Edit File-Format box. See File Formats below.

C: Import button

Click the Import button to import the Point-Cloud data-file.

The Point-Cloud is a continuous line in the graphic-area.

Data-Points

The File Format must include at least these terms:

•(x) (y) : if each data-point is an X and Y coordinate

•(Radius) (Angle) : if each data-point is a Radius and Angle coordinate.

Characters that are ignored in the data-file:

•Header lines, when entered as text.

•ASCII characters that are NOT: . , -, 0–9, in all lines.

Optional: Data Offset and Scale option

Options:

x , y

When you add a Point-Cloud, you select a Part. The Part has an Origin - its start-Point - where its XY coordinates are (0,0)

When the Point-Cloud has a measurement-offset of (X, Y), you can remove the offset. Enter (-X, -Y), which is the negative of the offset.

Or, to offset the Point-Cloud, by (X,Y), enter (X,Y) values.

File Rotary Units ; File Linear Units

Select the units that match those of the original Point-Cloud data-file

File Formats:

Pre-Select a File Format

To help you with the formatting, you can use the Pre-Select a File Format from the drop-down list-box.

MD-Dialog-PointCloud-PreselectFormat

When any of these formats do not represent the format of the data in your data-file, then edit the format in the Edit File Format box directly.

Example: Data-Files & File-Formats and the Enter File Format text.

Example 1: Data-File:

Example data-file to import as a Point-Cloud

Enter File Format: () () (x) (y)

Why?

Line 1	Is Not imported - text only (A, B, C, ... Z)
Line 2	Is Not imported - text only (A, B, C, ... Z)
Line 3 Column 1 & Column 2:	Is Not imported because of () () in the File Format () () (x) (y) removes these two Columns
Line 3 Column 3 & Column 4	Is Imported because the (x) (y) in the File Format () () (x) (y) identify that these Columns as x, y data
Lines 4, 5, 6, ...	Equal to Line 3

Example 2: Data-File

Data Format: N100 G00 X10 Y25 Z27

Enter File Format: () () (x) (y) ()

Why?

N100 G00 X10 Y25 Z27	Letters not imported (A, B, C, ... Z)
N100 G00 X10 Y25 Z27	Column 1, Column 2, and Column 5 - not imported - the () in the File Format () () (x) (y) ()
10 25	Imported - the (X) and (Y) in the File Format () () (x) (y) ()

Feedback Messages:

STEP 2: Fit Curve to Data

When you import Point-Cloud data, the chart shows the Point-Cloud data in (Cyan) and the Continuous Curve in (Pink).

In the chart below, the Continuous Curve does not follow the Point-Cloud data - this is intended and for illustration ONLY.

The two charts show as one chart after you successfully Fit the Continuous Curve to the Point-Cloud data.

Point-Cloud dialog > Fit Curve to Data tab

Parameters

Original Data Accuracy

This is a judgment you must make. Start with 0.1, then reduce it to approximately 0.001 - but see below for more thoughts.

Auto-Fit check-box and Fit Curve button

Usually, click the Auto-Fit button to make it active - see options

Increase the # Harmonics

Edit the # Harmonics

The Continuous-Curve becomes nearer to the Imported Data as you increase the # Harmonic.

Fit-Quality =0 >> 1

When Fit Quality Traffic Light becomes Green, ...

When the number in the Fit-Quality Number box is near to, or equal to, one(1), ...

... STOP - do not increase the number of Harmonics.

Display Options

Click one of the four radio-buttons

○Show Nothing

○Points only

○Points and Curve

○Curve Only

The view of the Continuous-Curve and the Point-Cloud in the graphic-area match the P, V, or A button.

Steps to do:

A.Edit the # Harmonics

☑Auto-Fit Check-box

The Curve updates immediately each time you edit the # Harmonics

❑Auto-Fit check-box is clear.

The Curve only updates when you click Fit Curve

B.Do A again

Do until the Fit-Quality and the Traffic-Light becomes Green or Orange

Velocity and Acceleration Graphs and Filter Width

The default plot is for Position. If you want to look at the plot of the Point-Cloud as Velocity or Acceleration (), then click the V or the A icons.

If the plot of the Velocity or Acceleration data is noisy you can smooth the noise (remove the noise) with the Filter-Width. This may help you identify the original Motion-Law.

Original Data Accuracy

Thoughts:

•Consider an Original Data Accuracy of 0.1, then reduce it to approximately 0.01.

•Do not enter a value that is more accurate than the original accuracy of the data. For example, if the data has 2 d.p. , then 0.05 OK, and 0.001 is not a sensible value. However, experiment, as you find that more accuracy gives you better results.

•Is the skill of the person that measured the Cam-Profile a factor?

•Is the cam clean? Is the cam worn? Is the cam damaged?

Machine Measurement Accuracy Approximations: per 100mm Diameter of Cam Diameter:

•Temperature-Controlled (18-22ºC) CMM approximately 0.2 - 5µm

•Non-temperature-controlled CMM approximately 2 - 10µm (~h4 for a 100mm shaft)

•Portable CMM approximately 5 - 20µm (~h5-h6 for a 100mm shaft)

•Test Rigs are variable, but you should aim for approximately 20 - 100µm (~h8-h9 for a 100mm shaft)