Coordinate Measuring Machine
“Preparation for Measurement”
Overview
Coordinate
measuring machines are high‑precision inspection tools designed to
measure parts. A computer equipped coordinate
measuring system offers faster, more accurate part inspection than conventional
surface plate equipment. The computer carries out the complex, time‑consuming
calculations for you and the computer software, Micromeasure III, helps you
inspect the part. The purpose of
this tutorial is to explain how to use Micromeasure III. Among the topics
covered are:
•
The principles of a coordinate system
•
An overview of the Micromeasure software
•
Instructions for planning a measurement routine
•
Step‑by‑step instructions for basic machine operation, including
start‑up, probe installation,
measurement
routines, and the creation and execution of a measurement file.
The tutorial is
designed to help you get started measuring parts with Micromeasure. It is
assumed that DOS and Micromeasure are already installed on the computer. If
they are not installed, see the Appendix Section of the User's Manual. By
taking you through sample routines, the tutorial demonstrates the process for
measuring a part. All measurement routines are similar, making operations very
straightforward. You will continue to learn about the system as you gain actual
experience.
If you have difficulty
with any part of the tutorial, try that section again. For more information
about the software routines not included in the tutorial, refer to the other
sections in this manual or to the "Help" screens that are accessable
from the Micromeasure screens. An explanation of how to access the
"Help" screens is covered in the User's Manual.
This tutorial is
intended to be used with the demonstration block, a 1/4" rigid or
electronic probe tip and English units of measurement. Your results may differ
slightly from those printed in the tutorial depending on your measuring skills
and variations in the demo block. The demo block's purpose is to allow you to
gain experience using the Micromeasure system. The block is not a high
accuracy part and is not meant to confirm machine accuracy. If other equipment
is substituted, the results will not be similar to the information that
appears on the tutorial screens.
All available software
routines are listed on the "Main Menu" screen. All entries can be
made with either the keyboard or a light pen. Because most of the functions can
be performed with a light pen, typing skills are not required. To make a
selection, you touch the screen with the light pen or move the cursor to a
field and press "Return". The tutorial is written as though you are
using both the light pen and the keyboard. Micromeasure also provides easy to
use pictures on the screen that show an example of where hits should be taken.
This means, that even if you have never used a computer or coordinate measuring
system before, you will be able to inspect parts quickly and accurately with a
minimum of effort.
To use this manual,
you will need the following:
•
A coordinate measuring machine
• User's Manuals,
including
‑ Micromeasure Tutorial
‑ User's Manual
for Micromeasure III
‑ User's Manual for CMM
• Accessories,
including:
‑
Touch Trigger Probe (electronic probe) with stylus or
‑
1/4" diameter rigid ball probe
‑
3/4" diameter requalification sphere
-foot switch for use
with ball probe or pickle switch for use with
electronic probe
-demonstration
block
The Coordinate System
To use Micromeasure it is important to understand the principles of a coordinate system. This system is a way to describe the location of points using perpendicular lines. A coordinate measuring machine uses a coordinate system to measure parts.
Figure 1. Coordinate System
A coordinate system consists of three axes that lie perpendicular to each other. The X‑axis runs left to right, the Y‑axis front to back and the Z‑axis up and down. On a coordinate measuring machine, the carriage moves along the X‑axis, the bridge along the Y‑axis and the Z‑rail along the Z‑axis.
Point of Origin and Measuring Range
The
point in space where all three axes meet is the point oforigin (XYZ = 0,0,0).
Its position is defined by the user and isusually located somewhere relative to
the part being measured. All distances are measured from this point. The point
of origin separates each axis into positive and negative sides.The axes are
divided into units of measurement, or coordinates, beginning at the point of
origin. Micromeasure can display coordinates in either Inch (English) or
millimeter (Metric) units. The distance along each axis that can be measured by
the coordinate measuring machine is called its measuring range. The range of
all three axes combined is called the measuring envelope.
Coordinates
The
point of origin can be placed anywhere, either on the part or off the part. In the
following
illustration,
the point of origin is at the lower front corner of the part. If a part is
positioned somewhere in the coordinate system, the location of any point on it
can be described using X, Y and Z coordinates. For example, the coordinates
for point A on the part are ‑4.5 on the X‑axis, 0 on the Y‑axis,
and +3.5 on the Z-axis. Point B is at ‑2.5 on the X‑axis, 0 on the
Y‑axis, and+4.5 on the Z‑axis.
Taking Measurements With the Coordinate
System
When
a part is inspected with Micromeasure and an electronic touch trigger probe
(TTP), The probe button on the mouse
needs to be turned on.
Probe button Hits
are then taken by touching the probe to the feature to be measured. When the
probe deflects, the computer will emit a 'beep' to indicate it has recorded a
measurement and the 'Number of hits' shown on the screen will increment. Each time a hit is taken, the X, Y and Z coordinates are
recorded by the computer. By locating a number of these points, Micromeasure
can define a feature, such as a bore, or the relationship between two features,
such as their distance apart or their perpendicularity. The part being inspected has its own X, Y and Z axes. As
you can imagine, a part placed randomly on the table surface would not be aligned
with the axes of the machine. With Micromeasure, the part is aligned by taking a series of
measurements on the part. This tells the computer the coordinates of the
part's axes. The computer then compares these measurements to the machine's axes
and reconciles the two through a series of calculations. This is one of the
benefits of having a coordinate measuring machine equipped with a computer. Software Software is the set of instructions that
operates the computer. These instructions, along with your input,
allow the computer to guide you through an inspection routine and perform complex
calculations. The Micromeasure software is installed in the CMM's computer. Using the Keyboard You
can use the keyboard to make all entries. Use the arrow keys to move the cursor
up and down the screen to different fields. Press the 'Enter key (instead of
the 'Done' softkey) to indicate completion. The software will recognize if you
are using the keyboard or the mouse and will automatically allow you the use of
the keyboard numeric pad or display the screen keypad. The Brown & Sharpe
supplied keyboard has a separate cursor keypad, however, if you are using a
keyboard that combines the cursor arrow keys and the numeric keypad, you must
use the numbers across the top of the letter keys in order to enter numbers.
You must also use the arrow keys to select the Message option. Messages and
Labels must be typed on the keyboard. Messages are instructions to the operator
and will appear on the monitor in the measurement screen during execution of a
measurement file. Labels are explanations of the Print Preview information that
appear on the monitor or printout during execution. Screens Micromeasure
consists of a series of screens that require you to either choose an item
from the screen or to take a measurement. Micromeasure is menu‑driven,
which means that you will move through the software by going from menu to menu. You choose the functions that you want
from each menu. The screens are
arranged in the sequence that is used for inspecting a part. This sequence is
illustrated in the flowchart on the
preceding page. The software is divided into three major sections: •
Start‑up • Selection • Preparation, Measurements, & Results The
first section, “Start‑up”, describes the starting process which is either
full start‑up or automatic start‑up. Full start‑up is used
when the system is first turned on or if the home position must be
reestablished. The home position must be reestablished if you leave the DOS
(Disk Operating System) or if the probe is disturbed. Full start up is also
performed when the system is first initialized or if power is turned off.
Automatic start‑up is used if you leave Micromeasure, but do not turn off
power or exit DOS. In automatic start‑up you go directly to the Main
Menu. The
second section, “Selection”, allows you to select the appropriate operating
modes, utility functions and measurement routines. The
third section, 'Preparation, Measurement & Results', contains the routines
for taking actual measurements and for calculating and providing results. Softkeys The
screens have certain features in common, such as the softkeys. These are a
series of functions that
are listed onthe bottom of the screen. They are used to initiate
commonactivities, such as switching to another screen or indicating that you
are done with an operation. The softkeys can be activated
by any of the following methods: •
Moving the cursor to the softkey and pressing “Enter”. •
Using the Function keys located on the top row of the keyboard. Function keys
F1 through F4 will select the softkey functions on the top row and Function
keys F5 through F8 will select the
softkeys on the bottom row. The Micromeasure Users Manual gives a detailed
explanation of each of the softkeys available with this program. Help Screens Each
Micromeasure screen has help screens that explain the purpose of a screen, its
contents, and how
to use the screen. Select the 'Help' softkey to access a help screen. If there
is more than one 'Help'
screen for a Micromeasure screen, “Nxt Scrn”
will display in the softkeys at the bottom of the first help screen. Selecting
this softkey will display the next 'Help' screen. Selecting 'Prv Scrn' will
take you back to the previous 'Help' screen. Block Numbers The
structure of Micromeasure is based on a block system. Each block represents a
separate function or routine in a measurement file. Each measurement file is a
series of blocks arranged one after another in the order in which the file is
to be executed. Measurement blocks consist of the combined information from a
measurement screen and its print preview screen. Other blocks contain alignment
and qualification information. The block number of a screen appears in the
lower right hand corner except when an exist ing measurement file is selected
from the Utility screen. In that case, the number in the lower right corner is
the total number of blocks in that measurement file. You can correct or change the information contained in a
block by means of the Edit Mode. This mode uses block numbers as a means for
selecting specific blocks and restructuring the sequence in the file. The
editing is simple since all the information about a particular measurement or
alignment is contained in one block and is displayed on the screen at one time. Operating Modes Micromeasure
III has three operating modes: Measure, Edit and Execute. Measure Mode is used to
measure a part and create a measurement fife. It is the default mode and is
indicated by the word 'Measure' in the
upper lrft corner of the screen. The Edit Mode is used to make changes in the
measurement file. The Execute Mode is used to run a previouslycreated
measurement file in order
to inspect a group of parts. To change from one mode to another, press the
light pen against
the word such as 'Measure' (or place the cursor over the word and press
'Enter'). A menu will appear from which you can choose 'Measure', 'Edit', or
'Execute'. Print Preview Screen The
Print Preview screen displays a variety of information about the measurement
just taken. With
this screen you can set the Probe Sense, Mode, Format, Printer, and Statistics
options and enter
a Label. In the Measurement Mode, the Print Preview screen will appear on the
monitor after each completed measurement. If the printer option is set to
'Yes',the Print Preview screen information
will also print out on the printer.
In the Execute Mode, the Print Preview screen will appear on the monitor only
if the printer option is set to 'No'. If the option is set to 'Yes', the Print Preview screen information will appear only
on the printout. The User's Manual gives additional information
about the types of information that can be enteredinto the Print Preview
screen. Preparation for Measurement Before you actually measure a part, you must
perform a series of preliminary steps to ensure that your measurements will be
accurate. Every time you inspect a new part you will perform the same steps: 1. Plan the
measurement routine 2.
Mount the part 3.
Start up the machine 4.
Find the machine home position 5.
Locate the reference sphere position 6.
Install the probe 7.
Select the operating configuration 8.
Qualify the probe tip 9.
Align the part Planning the Measurement This
section of the tutorial will explain how to do all these Routine steps.The
following section "Measurement", will provide step‑by‑step
instructions for measurement routines. Planning how to
measure a part before you begin will help to prevent delays and mistakes during
the creation of the measurement file. On the following pages the procedure for
planning your measurement routine is broken into four steps. To make your part
plan, just follow the steps. of
the part in relation to the CMM table. You can move the datum during an
inspection, if the nature of the part requires more than one origin. • Will the measurement
be in inches or millimeters? • How many probe
positions must be qualified? • What type of
alignment should be used? • Which features are
to be measured? • Which feature
relationships (for example, perpendicular lines) are to be created? • Which feature
characteristics (for example, straightness) are to be calculated? • Will nominals and
tolerances be used? • What is the
configuration information for this part? • What Messages or
Labels are to be included? • What filename will
be used? • What probe sense
(for example, inside or outside) is needed ? • What probe
approaches should be used in order for Micromeasure to sense the correct probe
compensation (and direction point)? Demonstration Block Part Plan The part plan for the Demonstration block might look as
follows: Filename---------Demo Measurement---Inches Probe Positions-2 ( one Straight Down and one 90 degrees towards the front) Working Plane- XY and ZX Origin----------- Counterbore Alignment------ Separate Origin (measure front line) Features to Measure – See Chart Below Mounting the Part You
are now ready to mount the part on the CMM table. Part mounting and alignment are
easy with Micromeasure because the computer takes care of the compensation
between the part and the machine coordinates. Because of this you do not have to be so precise in the physical
placement of the part. 1. Remove everything
from the CMM table except for the part to be measured and the reference sphere. 2. Place the reference
sphere within the measuring envelope in a position where it will not interfere
with part measurement. This is usually in the rear right or left corner. 3. Position the part
within the measuring envelope, toward the front of the table. If possible, the
part's major axis should be approximately parallel to the machine's major axis.
The major axis defines the axis about which the other two axes are defined. The minor axis is perpendicular
to the major axis. In an XY working plane, X is the major axis and Y is the
minor axis. While most features to be measured are in the top surface, one of
the holes to be measured lies on the rear surface (ZX plane). It is necessary
that the horizontal (forward facing) probe tip reach this hole. This will
probably require that the demo block be elevated above the
granite table.
