Coordinate Measuring Machine (CMM) http://en.wikipedia.org/wiki/Coordinate-measuring_machine

Coordinate Measuring Machine (CMM) http://en.wikipedia.org/wiki/Coordinate-measuring_machineKAMARUL ADNANLearning OutcomesAt the end of this lesson, students will be able to:Describe the principle of CMM.State the applications of CMM. Explain the operating methods of CMM.

IntroductionA 'coordinate measuring machine' (CMM) is a device for measuring the physical geometrical characteristics of an object.This machine may be manually controlled by an operator or it may be computer controlled.Introduction (Contd)

CMMIntroduction (Contd)

CMMIntroduction (Contd)Measurements are defined by a probe attached to the third moving axis of this machine.This probe touches the part of interest and allows collecting discrete points on the object's surface.

Introduction (Contd)

ProbeIntroduction (Contd)

Methods of probingIntroduction (Contd)The typical CMM is composed of three axes, an X, Y and Z. These axes are orthogonal to each other in a typical three dimensional coordinate system.Each axis has a very accurate scale system that indicates the location of that axis. All three axes are displayed on a digital readout. Introduction (Contd)Reverse Engineering

Propeller model being probed so that a 3D CAD drawing of the surfaces could be obtained.

Introduction (Contd)Quality Control

CMM used to verify dimensions of machined features

Introduction (Contd)A coordinate measuring machine (CMM) is also a device used in manufacturing and assembly processes to test a part or assembly against the design intent.By precisely recording the X, Y, and Z coordinates of the target, points are generated which can then be analyzed via regression algorithms for the construction of features.Introduction (Contd)These points are collected by using a probe that is positioned manually by an operator or automatically via Direct Computer Control (DCC).

Parts Of CMM MachineCoordinate-measuring machines include three main components:The main structure which include three axes of motion Probing system Data collection and Reduction system - typically includes a machine controller, desktop computer and application software. Parts (Contd)

Fixed Bridge Coordinate Measuring MachineMoving Bridge Coordinate Measuring MachineParts (Contd)

Fixed Table Cantilever Coordinate Measuring MachineColumn Coordinate Measuring MachineParts (Contd)

Probing SystemUses/ApplicationsThey are often used for:Dimensional measurement Profile measurement Angularity or orientation measurement Depth mapping Digitizing or imaging Shaft measurement

FeaturesThey are offered with features like:Crash protection Offline programming Reverse engineering Shop floor suitability SPC software and temperature compensation. CAD Model import capability On contact, the coordinate position are recorded by the CMM controller, adjusting for over travel and probe size.Positioning of the probe relative to the part can be accomplished either manually or under computer control.Methods of operating a CMM are classified as i) manual control, ii) manual computer-assisted, iii) motorized computer-assisted, and iv) direct computer control.Operation of CMMIn manual control, a human operator physically moves the probe along the axes to contact the part and record the measurement.The probe is free-floating for easy movement.Measurement are indicated by digital read-out, and the operator can record the measurement manually or automatically.Any trigonometric calculation must be made by operator.Method of Operating- Manual ControlThe manual computer-assisted CMM is capable of computer data processing to perform trigonometric calculations.Types of computations include determining hole-centre locations.The probe is still free floating to permit the operator to bring it into contact with part surfaces.Method of Operating- Manual Computer-AssistedMotorized computer-assisted CMMs power drive the probe along the machine axes under operator guidance.A joystick or similar device is used to control the motion.Low power stepping motors and friction clutches are used to reduced the effects of collisions between probe and part.Method of Operating- Motorized Computer-assistedDirect computer-control CMM operation like a CNC machine tool.It is computerized inspection machine that operates under program control.The computer also records measurements made during inspection and performs various calculations associated with certain measurement (for example, computing the centre of a hole from three or more points on the hole surface). Method of Operating- Direct Computer ControlBasic Geometric ElementsCircle: Requires 3 points for measurement: By measuring 4 (up to 50) or more points form deviation is determinedPlane: Planar measurements require 4 or more points for form. The intersection of Planes 2 and 3 generate Line 5; Point 6 is the intersection of Plane 4 and Line 5

Basic Geometric ElementsCylinder:To define a cylinder, 5 points are necessary. Calculations provide its axis and diameter. The intersection of the Cylinder 7 and Plane 4 is Line 8.Cone: The cone (or taper) requires at least 6 points for definition. Calculations determine the cones included angle and its axis in space.

Basic Geometric Elements

Sphere: The location of a sphere is found by measuring 4 points is also calculated.

The basic capability of a CMM is determination of coordinate values where its probe contacts the surface of a part.Computer control permits the CMM to accomplish more sophisticated measurements and inspections, such as:a) determining center location of hole or cylinderb) definition of a planec) measurement of flatness of a surface or parallelism between two surfaces, andd) measurement of a angle between two planes.CMM Measurements and AdvantagesAdvantages of using coordinates measuring machines over manual inspection methods include:1) Higher productivity-a CMM can perform complex inspection procedures in much less time than traditional manual methods.2) Greater inherent accuracy and precision than conventional methods.3) Reduced human error through automation of the inspection procedure and associated computations.A CMM is a general purpose machine that can be used to inspect a variety of part configuration. CMM Measurements and AdvantagesA CMM is a general purpose machine that can be used to inspect a variety of part configuration.

CMM Measurements and AdvantagesConclusionWith the prices of desktop computer dropping drastically in the last few years, small manufacturing firms can afford to own a CMM with a computer interface.CMMs are slowly working their way into automation.With the major emphasis being on closed loop process control, CMMs provide the ability to make precise measurements, using the sophisticated hardware, and convert this information using integrated software, into data that is meaningful to the entire automated system.