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.
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.
The Point-Cloud FB is now in the graphic-area and the Assembly-Tree.
STEP 1: Identify and enter the formatting of the Point-Cloud data text file you want to import.
The Point-Cloud data file must include:
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:
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
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.
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.
Click the Import button to import the Point-Cloud data file.
Go to 'STEP 2: Fit Curve to Data' tab
When you successfully import Point-Cloud data, the chart displays the:
- and -
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 Quality is near or equal to one.
You must use the Point-Data Accuracy and # Harmonics 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 Quality [of the Continuous-Curve] near, or equal, to one, and the Traffic Light Icon to be Green.
Fit a Continuous Curve to the Point-Cloud Data
Enter the Point-Cloud Data Accuracy parameter.
Note 1: Typical Measurement Equipment Accuracy
Typically: for each 100mm of Cam Diameter, the accuracy of a:
Note 2: Cam Measurement Accuracy
If the Cam is worn, try to measure points around the cam that are not worn, or are less worn.
Click the Auto-Fit... check-box to put a tick in the check-box
The Continuous-Curve updates each time you edit the # Harmonic.
Edit the # Harmonics until you see the Fit Quality Traffic Light become Green, and the value in the box near or equal to one.
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 button to update the Continuous-Curve,
Notes: # Harmonics
When the Traffic-Light becomes Orange or Green, do not add more harmonics
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-area
Click one of the four radio buttons:
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 (), 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 Width 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.