Point - Surface IJK Vector

1,2,3,4,5,6,7,8,9	Measure→Point
Keyboard	Main Menu	Toolbar

Points are dimensionless locations is 3D space. Points have no size. The location of a point is specified by its X, Y, and Z coordinate in a particular coordinate system. There are many points that Geomet support. These include 1D, 2D and 3D points.

Measured points consist of 1D, 2D and 3D style geometric elements. keyboard access to these points are done through the number keypad, see table 1.

Keystroke	1D Point	2D Point	3D Point
1	-Z
2	-Y
3 + 2		XY IR
3 + 4		ZX IR
3 + 6		YZ IR
3 + 9			3D IR
4	-X
5 + 2		XY
5 + 4		ZX
5 + 6		YZ
5 + 7			Vector Point
5 + 9			3D
6	+X
7 + 2		XY OR
7 + 4		ZX OR
7 + 6		YZ OR
7 + 9			3D OR
8	+Z
9	+Y
IR = Inside Radius / OR = Outside Radius
table 1, Keyboard Access

Vector Points

A Vector Point provides the capability to measure the deviation from nominal of a target point on any arbitrary surface, given the XYZ location of the 3D target and the nominal unit vector components I, I, and K at the target.

Geomet offers several modes to capture Vector Points. Each mode is designed to enhance your ability to capture surface data points from all or some known data. These methods are:

• Method 1 - No nominal are known
• Method 2 - IJK Normal Vector is known
• Method 3 - XYZ Nominal Target is known
• Method 4 - XYZ Nominal Target and IJK Normal Vector are known
• Method 5 - Vector Point Import

To activate the Vector Point screen, press the <5 + 7> keystroke on the number keypad.

figure 1, Vector Point Screen, Manual Version

To better understand the application of Vector Points, please refer to Technical Note #1, "Curved Surface Measurement with Vector Point".

While the percentage of Geomet users who have made extensive use of the vector point function is small, some have come to regard it as indispensable, and every now and then another Geomet owner discovers the wonders of vector point. Invariably, this discovery is followed by about two weeks of daily and lengthy phone conversations between the user and our application support engineers, during which the workings and benefits of the function gradually become clearer to the user. In an attempt to shorten this process, we have written a Technical Note, "Curved Surface Measurement with Vector Point", that contains a description of its workings and some suggested experiments that might be used to gain familiarity with the problems of curved surface measurement on a manual CMM. This technical note is long and likely boring for anyone without a serious interest in the problem.

Should your interest in vector point survive the reading of that technical note, you may also be interested in another Technical Note, this one titled, "Automatic Generation of Vector Points for DCC CMMs". This note details the process used to create a working solution to capture large vector point data clouds on complex surfaces.

Tolerance of Vector Points is available in Cartesian, Polar or RFS Positional Tolerance formats.

All Vector Point methods provided by Geomet are designed to give the operator the greatest flexibility to capture vector points with varying known data. The reporting characteristics of vector points remain the same for all methods used.

figure 2, Vector Point Report

In the vector point report, the XYZ actual surface point values, nominal deviation and linear deviation from nominal are shown under the Actuals, Dev. Nom.  and Nominals columns respectively. Additional data reported include Normal Deviation (N Dev.) and Probe Deviation (Pr Dev).

Normal Deviation is the deviation along the Vector Normal from the actual data point. When applying a profile tolerance on a arbitrary surface, the Normal Deviation reports where in the profile band the actual point resides.

Probe Deviation is the distance from the actual data point to the axis of the Vector Normal. This value provides a understanding on the quality of the actual data point against the expected target point. Under normal conditions, this value should be small, but can be adversely affected based quality of the drive along the Vector Normal approach.

To begin, we will start with Method 4, where the XYZ Nominal Target and IJK Normal Vector are known, as shown in figure 1 under the Method group.

This method requires that you know the XYZ target and the IJK surface vector normal at that target point. In our examples, we will utilize a 1" diameter reference sphere. Start by establishing a XYZ Origin on the center of the sphere. Utilize the orient and alignment of the MCS by creating a PCS with the ICS→PCS function.

Step 1

Enter the nominal XYZ target and the IJK normal vector values.

figure 5, Enter XYZ / IJK Values

Step 2

Press the <Ok> button or press the <enter> key on the keyboard. The Target Positioning dialog will show where the probe is currently in relationship to where the probe should be to capture the vector point.

figure 6, Target Window	figure 7, On Target Positions

In figure 6, the distance to the position the CMM is required to be at is shown under Target Position. In this example, there are symbols next to X and Y showing a "closed lock". These are the suggested axis Geomet has determined you should move and lock over the targeted XYZ point. Should access to the target point be limited where another axis must be used to approach the target, select the desired direction in the Approach Selector group. The lock symbols and target values will update based on your selection.

NOTE: If the Digital Readout is activated, the DRO will display the Targeting Position to allow better visual appearance at a greater distance.

NOTE: The color of the XYZ Targeting display showing on position can be adjusted, see Geomet System Options.

figure 8, Manual Target Approach

Locate the probe over the target axis specified, lock the CMM with the axis locks and use the fine adjust knobs until the X and Y values approach 0.0000". When inside the allowable position values as determined by the probe deviation, the readout will turn green in color as shown in figure 7.

Next, carefully move the probe down along the -Z axis until you come in contact with the part, see figure 8. Geomet will capture that point and report the actual XYZ location and deviations.

Upon completion, the vector point routine will return to the main vector point dialog for additional instructions.

Step 1

figure 9, Vector Point, DCC Version	figure 10, Enter XYZ / IJK Values

Enter the nominal XYZ target and the IJK normal vector values, see figure 10.

Step 2

figure 11, DCC Target Dialog

Press the <Ok> or <AutoRun> button or press the <enter> key on the keyboard. The Target Positioning dialog will show where the probe is currently in relationship to where the probe should be to capture the vector point, see figures 11.

figure 12, DCC Approach Vector

Move the CMM teaching IPs until you are over the expected Stand Off, SO, on the approach vector. Press the <AutoRun> button and the CMM will reposition over the expected target point along the IJK surface normal vector at the standoff location, see figure 12. When at the stand off location the probe will commence to capture the vector point driving down the surface normal vector.

NOTE: The accuracy of moving along the approach vector is greatly influenced by the speed of approach and length of approach. To obtain the greatest control, it is better to have a slower approach speed which is controlled by the probing speed and is set in the DCC Options page. To increase the approach distance, the value can be set on the Vector Point page and is shown in figure 8.

Method 1 offers the user a chance to obtain approximate IJK and arbitrary target data build tools. This method is most likely to provide good results of planar surface in any orientation. It is designed to allow the operator to perform a IJK approximation by gathering 3 - 5 data points from which Geomet will calculate a IJK to be used as the Vector Normal.

figure 13, Method 1 - No Known Data

To begin Method 1, select the "No Data" choice in the Method group. the Vector Point tool will reconfigure itself as shown in figure 13. The only data that can now be entered is the Upper / Lower Tolerance and Probe Deviation.

Step 1

To begin the measuring process, press the <Ok> button. The Vector Point tool will disappear replaced with a message in the Geomet Prompt area stating "IJK Approximation" and a countdown of 3.

Capture 3 data points surrounding the target area for the vector point. These points should be sufficiently spaced apart to assure confidence that the captured data points will solve the algorithm for a plane. Should the points be too close together, an error can be introduced caused by the influence of the repeatability of the touch probe and CMM structure. If the surface you are working with is a known flat plane, spread the data points out.

Step 2

After the IJK Approximation data points have been captured, the Geomet prompt will now display "Measure Vector Point". Capture the vector point.

Geomet will cycle back to Step 1 waiting for the next IJK Approximation.

Performing Method 1 on a DCC style CMM offers a greater degree of accuracy on arbitrary surfaces. The process still requires an IJK Approximation which becomes a process that the CMM will perform.

figure 14, DCC Method 1	figure 15, Capture Target Point

Step 1

As seen in figure 14, the Default DCC Settings group is available when the CMM is a DCC style. Enter a proper standoff distance for the vector point. Enter a number of points to be used to determine the IJK Approximation in the control labeled 'No. of Hits". Acceptable value for number of hits is 3 - 5. Enter a diameter value the CMM will use to capture the IJK Approximation points. Normally a small diameter such as 0.3" works well. Press the <Ok> button to proceed.

Step 2

The Vector Point Positioning dialog will appear, see figure 15. You are now instructed to capture the target vector point on the surface.

figure 16, Start Approximation	figure 17, Calc Approximation	figure 18, Capture Vector Point

Step 3

When the target point has been captured, you are instructed to move the probe over the target point and press the <IP> button on the joystick.

Step 4

The CMM will calculate a motion path based on the diameter and number of hits required for the IJK approximation. The CMM will then capture the data points under DCC control, see figure 17.

Step 5

When the IJK Approximation has been completed, the CMM will move to the stand off position on the new vector normal and capture the target vector point to complete the process, see figure 18.

Method 2 offers the user a chance to obtain vector points on surface that have a known IJK surface normal. This method is designed for use on planar surfaces and can be used to capture many vector points quickly.

figure 19, Method 2 Known IJK

Step 1

Enter the known IJK values in the edit controls and press <Ok>

Step 2

Geomet will prompt you to capture vector points on the designated surface. Upon capturing the data point, Geomet recycles step 2.

Method 2 on a DCC style CMM requires the same steps as on the manual CMM. Please refer to Steps 1 and 2 listed above. It is important that a proper motion path is built by using a proper stand off distance and IP points between vector points.

NOTE: Method 3 is only available on DCC style CMM and will be disabled on manual CMMs.

This method requires that the target XYZ position of the vector point be supplied. Geomet will build from that target an IJK approximation by capturing data points on a diameter path around the target point and calculating an IJK vector normal.

figure 20, Method 3 Vector Point	figure 21, Start IJK Approximation

Step 1

As seen in figure 20, the Default DCC Settings group is available when the CMM is a DCC style. Enter a proper standoff distance for the vector point. Enter a number of points to be used to determine the IJK Approximation in the control labeled 'No. of Hits". Acceptable value for number of hits is 3 - 5. Enter a diameter value the CMM will use to capture the IJK Approximation points. Normally a small diameter such as 0.3" works well. Press the <Ok> button to proceed.

Step 2

The Vector Point Positioning dialog will appear, see figure 21. You are now instructed to position the CMM probe over the target point and press the <IP> button on the joystick.

Step 3

The CMM will now calculate a motion path based on the IJK Approximation diameter and number of hits centered on the target point and execute data point capturing, see figure 22.

Step 4

Once the IJK Approximation has been calculated, the CMM will move to the stand off point above the targeted vector point and commence capturing the actual data point, see figure 23.

Method 5, when chosen sets Geomet up to read in an ASCII Vector Point data file that contains all necessary targeting, vector normal and motion commands to measure vector points.

Microsoft Excel and Microsoft WordPad has be used to demonstrate how to build ASCII files to be used in Vector Point import. The samples are available for download below. When building a table, Geomet uses keywords followed by a parameter list which describes a operation. These keywords can be found in the Vector Point Import Table.

VP Example Files	Download All Examples
VP Examples #1
VP Examples #2
VP Examples #3
VP Examples #4

The table is made up of 2 main sections. These are the Header and Block Descriptions. The Header is data that can set a global setting for use by all Blocks. Block Descriptions contain the actual targeting data and supporting tolerance, motion, probe and text data.

Keywords used in the table are not upper or lowercase sensitive and can be entered in either. Geomet always interprets keywords in uppercase and performs the operation automatically.

The header has limited keywords that control the global settings for their respective features.

Keyword	Description
U:	Unit of Measurement
S:	Stand Off Distance
O:	Over Travel Distance
H:	Upper Tolerance Value
L:	Lower Tolerance Value
E:	Probe Deviation

An example of a header would be:

U:	Inch
S:	0.50
O:	0.50
H:	0.001
L:	-0.001
E:	0.0002

Should any of the header items be missing from the ASCII import file, Geomet will prompt for a starting value when the file is opened. This does not apply to Unit of Measure. The keywords shown above can also be used in Block Descriptions.

An imported data file can contain many blocks of data defined by a 'start' and 'stop' keyword. This allows organization of common Vector Points. For example; a block of vector points may contain all necessary points required for the top surface of the part being inspected. A second block can be used to group all vector points for the front surface.

The process of building blocks of data can be helpful for use on DCC style CMMs. By grouping all common vector points, an auto run through the list can be done without concern of positioning the probe around corners or other obstacles. In example #3, we show how mixing vector points with interim points (IP) to create a complete motion path to capture data points on more than a side of the GeoWidget. Another use of blocks can be to group all common tolerance bands together.

A block is always started by the keyword "start" followed by vector point instructions and always ends with a "stop". An example might look like:

START
	Keywords / Instructions......
	Keywords / Instructions......
	Keywords / Instructions......
STOP

Creating the Vector Point ASCII data file in Excel is one method used where the power of a spreadsheets internal math functions can assist in developing the targeting tables.

For example, should you want to create a table of vector points that covers a large area using a uniform grid of rows and columns, Excel would be used with the fill range tools or copying formulas. In sample #4, you will see the spreadsheet uses formulas to step the vector points in a column by changing the Y target value, 0.25" between each point.

Saving the spreadsheet in a form that Geomet will read can be accomplished by saving in either file type:

• Formatted Text (Space Delimited)(*.prn)
• Text (Tab delimited)( *.txt)

To save into one of these formats, from Excel use the drop down menu [File→Save As], see figure 24.

figure 24, Excel File Save As Options

Choose one of the acceptable formats (*.prn) or (*.txt) in the "Save as type" drop down selections. Once the file type has been chosen, select <Save> and Excel will prompt you with a warning that not all formatting can be saved in this file type. Accept the warnings and continue saving.

Each keyword used in the Vector Point data file utilizes a fixed syntax for proper application. In some cases there are more than one syntax for a keyword. The tables below help to demonstrate the proper application.

keyword START

Identifies the beginning of a block. Must have a STOP keyword associated at the end of the block. There are no parameters following the keyword.

usage START

keyword STOP

Identifies the end of a block. Must have a START keyword associated at the beginning of the block. There are no parameters following the keyword.

usage STOP

keyword N:

Used within the START and STOP keywords to attach a label to the block. There should be only 1 N: associated with each block. The naming of a block is optional and should there be no name included, the label for the block will be a sequential number starting with 1.

usage N: Top Surface of GeoWidget

keyword U:

Unit of Measurement. Prepares the data to be imported and reported in metric or inch modes. This does not place a record in the current inspection report.

usage U:metric, U:mm, U:inch

keyword PROBE:

Activates a requested stylus. This feature will place a stylus record in the inspection report.

usage PROBE: 2

keyword M: -or- TEXT:

Places a standard Geomet text statement in the inspection report.

usage M:   Top surface of the GeoWidget

usage TEXT:   Top surface of the GeoWidget

keyword H:

Establishes the upper limit for the Vector Point profile band. The value attached to this keyword is sign sensitive.

usage H: 0.001

keyword L:

Establishes the lower limit for the Vector Point profile band. The value attached to this keyword is sign sensitive. Should you require a profile band of +0.001 / -0.001 you must enter -0.001 as shown below.

usage L: -0.001

keyword E:

Establishes the Probe Deviation or probing error limit. This value must be > 0.000.

usage E: 0.0002

keyword T:

Attaches Print Exception Tags on the reported Vector Point values based on the parameters shown after the keyword. The available parameters are X, Y and Z used alone or in any combination. for example, using the X alone will tag only the X reported value. Using XZ or ZX will attach a tag to X and Z values.

usage T:XYZ

keyword IP:, IP=, IP =

Creates a Interim Point (IP) used during DCC operations to traverse between XYZ locations. These values are entered in local Part Coordinate System values. There are 4 variants to entering Interim points, see usage.

An interim point has 3 values; X, Y and Z. The import filter will accept a space comma or tab between the values.

usage	X	Y	Z
IP:	1.234	2.345	3.456
IP=	1.234,	2.345,	3.456
IP =	1.234	2.345	3.456

keyword X: Y: Z: I: J: K:, X= Y= Z= I= J= K=

Creates the Vector Point target. This is the expected point of contact on a nominal surface. This value also is inserted in the tolerance nominal of the vector point being created. These values are entered in local Part Coordinate System values. There are 4 variants to entering Interim points, see usage. NOTE: to ensure compatibility with previous versions of Geomet, a target point can also be defined without any prefix values. In these instances, the XYZ and IJK values are entered in s columns and extracted into; column 1 = X, column 2 = y, etc.

An interim point has 3 values; X, Y and Z. The import filter will accept a space comma or tab between the values.

usage
1.10	2.20	3.30	0.00	0.00	1.00
1.10,	2.20,	3.30,	0.00,	0.00,	1.00
X:	1.10	Y:	2.20	Z:	3.30	I:	0.00	J:	0.00	K:	1.00
X=	1.10	Y=	2.20	Z=	3.30	I=	0.00	J=	0.00	K=	1.00
X =	1.10	Y =	2.20	Z =	3.30	I =	0.00	J =	0.00	K =	1.00

keyword PROBESP:

Updates the current probe speed for use on DCC style CMMs.
Valid limits: 0.010" - 1.000" (0.254mm - 25.4mm)

usage PROBESP: 0.25

keyword TRAVSP:

Updates the current traverse speed for use or DCC style CMMs
Valid limits: 0.01" - 20.0" (0.254mm - 508.0mm)
NOTE: Some CMMs have internal limits on maximum traverse speeds maybe less than the valid limit shown above.

usage TRAVSP: 10.0

keyword S:

Establishes the standoff distance for use with DCC style CMMs. This is the distance along the vector point surface normal (IJK) above the expected target point where the probe will position itself prior to commencing the measurement move to capture the XYZ target. This point along the vector normal is referred as a Stand Off point and is calculated at the time of executing the vector point data file.

The smaller the stand off distance, the greater chance of missing your target point. This is caused by the instability of the vector motion approach from the stand off point to the target point. The CMM will attempt to follow the IJK vector to the target point but is influenced by the mass of the CMM, the speed prior to starting the probe move, the speed of the probe move and the stability of the motor tuning. It is suggested, that a minimum standoff distance of 0.50" and a slower probe speed of 0.20" be used in all cases where possible.

One analogy to explain probe motion is to understand the physics of driving a car. Most drivers when approaching a corner will slow down to make the turn smooth. However, should you turn while driving too fast, your car will overshoot the expected turning radius. The driver will then have to compensate to get back to the center of the turning radius, or lane. The car will then overshoot the expected lane due to the mass of the car pushing beyond the center point. The car will then sway back and forth while stabilizing toward the center of the driving lane.

CMMs are no different. A heavy CMM will require slower speeds during tight turns or to follow a projected path accurately.

usage S: 0.50

keyword O:

Defines the Over Travel distance the probe will travel past past the expected XYZ measurement contact point. Should the probe movement reach this distance, all motion stops as a safety precaution.

The over travel distance should be sufficient to allow safe passage of the probe without allowing contact with the body or head of the probe.

usage O: 0.75

When the vector point ASCII data file has been opened, the execution of that data will be depend on whether you have a manual or DCC style CMM.

To execute, start by selecting the block from the data file in the drop down tool labeled "Select Block->", see figure 25.

figure 25, Select Vector Point Block

To execute the vector point information contained in the block on a manual CMM, select the <Ok> button from this dialog. The behavior of the targeting will be the same as defined in Manual Application of Method 4. However, the vector point import tool will supply the XYZ and IJK values with every entry in the data block.

Executing the vector point data file on a DCC system can be done in 2 methods. Depending on the information in the vector point data file, you can choose to execute one point at a time, or run the entire block.

Executing one point at a time allows the building of the motion map by manually teaching the probe path and entering IPs by pressing the IP button on the joystick. Geomet will provide a targeting box to the standoff point before the expected XYZ contact point, as described in DCC Application of Method 4. To perform this method, press the <Ok> button. When each point has been completed, the vector point import tool will advance to the next point in the data file and prompt you to proceed with the next step.

Should you have data blocks that includes all information necessary to allow safe transition of the probe between vector points, select the <AutoRun> button from the dialog. This will execute all vector points in the data block. In example #3, you will find a data block that contains all motion required to move the probe around the GeoWidget safely and capture several vector points.

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