Point-Cloud Tool dialog-box

See Modelling FB toolbar > Add Point-Cloud FB


Why use a Point-Cloud FB?

Use a Point Cloud to:

1.Import dataA as a text file.

Typically, you would measure a cam at discrete points with a Coordinate Measurement Machine (CMM).

The format of the data is 'Radius vs Angle', or 'X vs Y'.

2.Fit a smooth, continuous-curveB to the coordinate-data.

A continuous-curve is better than the coordinate-data for Cam Design and Analysis, and to reverse engineer a motion.


NotesA,B

Coordinate-data: the measurement data that is taken 'as is' [the raw data]. If you want to use the Coordinate-Data to get velocity, acceleration and jerk, you would need to differentiate the data with numerical techniques. Usually, the motion-derivatives would become 'noisy'.

Continuous Curve: a mathematical equation that is a 'good fit' to the coordinate-data. To obtain velocity, acceleration and jerk, we can differentiate the mathematical equation. The motion-derivatives of the function are 'smoother' than motion-derivatives of the Coordinate Data.

Add a Point Cloud element and Open the Point-Cloud dialog-box

Icon-FB-PointCloud

STEP 1.Add the Point-Cloud FB to the graphic area

A Point-Cloud is a child to Part.

1.Click Modelling FB toolbar > Add Point-Cloud FB

The Command-Manager shows one selection box

3.Click OK-tiny-11-15 in the Command-Manager

The Point-Cloud FB is now in the graphic-area and the Assembly-Tree.


STEP 2.Open the Point-Cloud dialog-box
1.Explore the Assembly-Tree to find the Point-Cloud FB as a child element to the Part
2.Double-click the Point-Cloud FB to open the Point-Cloud dialog-box

-or...

...see 'How to open a Dialog-Box'.

tog_minusSTEP 1: Import Data tab

STEP 1: Identify and enter the formatting of the Point-Cloud data text file you want to import.

Dialog-Point-CloudFB-Import-BrowseImportbuttonsDialog-Point-CloudFB-Import-FileFormat

Dialog-Point-CloudFB-Import-DataUnitsOffset

 

The Point-Cloud data file must include:

X , Y coordinates, or
R , Θ coordinates, if the data represent a 'circular' cam of sorts.

However, your data file may not have only two columns of data.

You must enter in the Edit File Format box the 'File Format' of the file you want to import.

Edit File Format box:

If there are more columns in the file, for example: 'X , Y , Z' ; or: 'Line # , X , Y' ; we must filter out the extra data.

What to enter as the file format:

Enter (x) and (y) for X–axis and Y–axis data.
Enter (Radius) and (Angle) for Radius and Angle data
Enter () to ignore columns of numerical data.

ASCII characters that are NOT: . , -, 0–9. are ignored.

E.G: If the File Format is

N100 G00 X0 Y0 Z0

Enter: ()()(x)(y)()

Optionally: Pre-Select a File Format

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

The drop-down list-box provides different formatting options to help you enter the correct format in the Edit File Format box

MD-Point-Cloud-Text-Format

You can edit any format to suit the formatting of you particular Point-Cloud data file.

Browse... button [at top, left of dialog]

When the format in the Edit File Format box is correct, click the Browse... button to select file you want to import.

'Open' the file.

Point-Cloud file-name:

After you find and open the file you want to import with the Browse... button

The file-name will show in the File-name to Import [Read-Only] box


x , y

When you add a Point-Cloud FB, you select a Part. The Part has an Origin, where the Part-Coordinates are X=0 and Y=0.

If the Point-Cloud data has an offset to it, then you can remove the offset with the X and Y parameter boxes.


File Linear and Rotary

Select the unit that matches the units of the Point-Cloud data.


Import button

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


Go to 'STEP 2: Fit Curve to Data' tab


tog_minusSTEP 2: Fit Curve to Data

Dialog-FB-PointCloud

When you successfully import Point-Cloud data, the chart1s-red displays the:

Point-Cloud Data in Dark Blue

- and -

Continuous Curve Graph in Light-Blue.

Note: The graph above shows a Continuous Curve that does not follow the Point-Cloud. This is to show the plot of the two graphs ONLY for the help documentation. The two charts should be virtually identical when the Fit Quality5s is near or equal to one[1].


You must use the Point-Data Accuracy2s and # Harmonics3s parameters to make the Fitted Curve (Light-Blue) nearly the same as the Point-Cloud Data (in Dark Blue).

The target is to make the Fit Quality5s [of the Continuous-Curve] near, or equal, to one[1], and the Traffic Light Icon5s to be Green.


Fit a Continuous Curve to the Point-Cloud Data

A.Original [Imported Point-Cloud] Data Accuracy2s

Enter the Point-Cloud Data Accuracy parameter.

Note 1: Typical Measurement Equipment Accuracy

Typically: for each 100mm of Cam Diameter, the accuracy of a:

Temperature-Controlled (18-22ºC) CMM is ~0.2 - 5µm
Non-temperature-controlled CMM is ~2 - 10µm
Portable CMM is ~5 - 20µm, and
Test Rig is variable, but you should aim for 20 - 100µm.

Note 2: Cam Measurement Accuracy

Do not enter an accuracy that is 'finer' than the data. For example, if the data is to three decimal places, then do not enter a value less than 0.001! In fact, 0.005 would be a sensible entry.
Think about the skill of the person taking the measurements, if it has a human element.
Is the cam clean? Is the cam worn? Is the cam damaged?

If the Cam is worn, try to measure points around the cam that are not worn, or are less worn.

B.Auto-Fit check-box and Fit Curve button4s

Click the Auto-Fit... check-box to put a tick in the check-box

The Continuous-Curve updates each time you edit the # Harmonic3s.

C.Edit the # Harmonics3s

Edit the # Harmonics3s until you see the Fit Quality Traffic Light5s become Green, and the value in the box5s near or equal to one[1].


You may need to clear the Auto-Fit check-box if the Point-Cloud Data has many points, for example more than 10000 points.

If you clear the Auto-Fit... check-box, you must click the Fit Curve button4s to update the Continuous-Curve,

Notes: # Harmonics

When the Traffic-Light becomes Orange or Green, do not add more harmonics4s

If you do, the curve will tend to oscillate with an amplitude of the Measurement Accuracy. The fitted plot will have an unnecessary ripple!


Display of the Point-Cloud Data and Continuous-Curve in the graphic-area6s

Click one of the four radio buttons:

Show Nothing
Show Points only
Show Point and Curve
Curve Only

Velocity and Acceleration Filter Width

Generally, you do not need to edit this parameter. If you want to look at the plot of the Point-Cloud as Velocity or Acceleration (8s), then click the V or the A icons.

If the Point-Cloud Data is noisy you can smooth the Velocity or Acceleration data. Use the Filter Width7s to remove some of the noise from the data. This may help you recognize the original Motion-Law.

However, do not make the Filter Width too 'wide' - or too 'smooth' - such that the velocity and acceleration curve become 'flat'. Experiment!

We numerically differentiate the Point-Cloud to derive this data.  However, the Continuous-Curve is a mathematical equation. The Magnetic-Joint will contact the Continuous-Curve and not the Point-Cloud data to give a much better estimation of cam so that you can reverse-engineer the motion much more accurately.

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd