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Unit II Coordinate Measuring Machines (CMM).pptx

Coordinate Measuring Machines (CMM): Types of CMM such as bridge, gantry, portable and horizontal arm, types of probes including touch trigger, scanning and optical probes, applications in reverse engineering and inspection.

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Unit II Advanced Metrology and Industrial Inspection Systems
• Coordinate Measuring Machines (CMM): Types of CMM such as bridge, gantry, portable and horizontal arm, types of probes including touch trigger, scanning and optical probes, applications in reverse engineering and inspection. • Optical and Non-Contact Metrology: Machine vision systems including image processing basics and industrial inspection applications, profile projector and toolmaker’s microscope, 3D scanning technologies such as laser scanning and structured light. • Thread and Gear Metrology: Thread parameters such as major diameter, minor diameter and pitch diameter, introduction to optical and CMM-based thread measurement, gear metrology including gear errors • Surface Metrology: Surface texture and parameters such as Ra, Rz and Rt, modern surface measuring instruments including stylus-based instruments, optical surface profilers.
Historical development and evolution of CMM technology • The first CMM is generally attributed to the industrial machine tool manufacturer Ferranti in 1959. The first of these CMMs was sold a year later in 1960 to the Western Electric plant in Winston-Salem, North Carolina, USA. The company reported a reduction in its measurement times from 20 minutes down to just one minute. • Five years later in 1965, an Italian company called Digital Electronic Automation (DEA), which is now part of Hexagon, sells the first gantry style CMM. • The first computer interface for a CMM came in 1967 developed by Data Corporation on behalf of Sheffield Corp. Three years later in 1970, Sheffield Corp goes on to provide the first commercially viable computer controlled CMM with automated inspection and servo driven X, Y, and Z axis. • In 1972, the dynamic touch trigger probe was invented, and the following year was the first continuous contact scanning probe. • In 2001, Hexagon acquires Brown and Sharpe, PC-DMIS, Leica Geosystems, Leitz, Optiv, Quindos, Romer, and TESA Technology (and others) to become the world’s largest supplier of metrology solutions.
• The term coordinate measuring machine refers to the instrument/machine that is capable of measuring in all three orthogonal axes. Such a machine is popularly abbreviated as CMM. • A CMM enables the location of point coordinates in a three-dimensional (3D) space. It simultaneously captures both dimensions and orthogonal relationships. • Another remarkable feature of a CMM is its integration with a computer. The computer provides additional power to generate 3D objects as well as to carry out complex mathematical calculations • A coordinate measuring machine (CMM) is a device that is based on the principles of 3- Dimensional Coordinate Geometry principles i.e., a Cartesian coordinate system with XYZ axes. • A CMM (Coordinate Measuring Machine) is a precision measuring machine used to check the size, shape, and position of parts.
• It works by touching (or scanning) a component with a probe and recording the exact X, Y, and Z coordinates of points on the surface. Using these points, the CMM tells us whether a part is within tolerance or not. • CMMs are widely used in manufacturing and quality control because they provide high accuracy, repeatable results, and reliable inspection of complex parts. • While optical and white light sensors do exist, mechanical and laser sensors are the most often utilized types of probes in CMM’s. • The probe location may be managed manually by an operator or it may be managed by a computer, depending on the equipment. A CMM machine is a device that uses coordinate technology to measure the dimensions of machine or tool components. • You may be able to measure the target and record the measured data depending on how sophisticated the CMM machine is.
Basic Construction and Working A standard CMM consists of three mutually perpendicular axes (X, Y, and Z) which enable movement in three-dimensional space. Since these three axes are perpendicular to one another, the machine's measuring space (work volume) is cuboidal. The main components include: X-axis: Provides longitudinal movement. Y-axis: Provides lateral movement. Z-axis: Provides vertical movement. Probe: Mounted on the Z-axis to touch or scan the workpiece. Drive Motors: Each axis is driven independently by a precision motor. Linear Measuring System: Precision scales continuously measure the exact position of each axis. Computer/Controller: Collects coordinate data and performs dimensional calculations.
Working Principle The workpiece is securely placed on the CMM table. The probe moves along the X, Y, and Z axes under computer control. Each axis has a precision measuring system that continuously records its position. When the probe touches the workpiece surface, the machine instantly records the X, Y, and Z coordinates. By collecting many such coordinate points, the software calculates: Length Diameter Height Angle Flatness Circularity Position Profile Other geometric dimensions and tolerances
Types of CMM Structures •Bridge CMM: Uses a moving or fixed table with a 3D moving bridge framework; it provides high accuracy for standard-sized machined parts. •Gantry CMM: Features upright pillars resting directly on the floor to accommodate exceptionally massive components like automotive bodies and aerospace chassis. •Portable CMM: Uses an articulated arm design that operators can move around or place directly on large workpieces for flexible shop-floor measurements. •Horizontal Arm CMM: Features a horizontal spindle ideal for inspecting sheet metal, long car parts, or environments requiring side access
Bridge CMM A Bridge Type Coordinate Measuring Machine (CMM) is the most commonly used type of CMM in industrial metrology. It consists of a precision granite table with a bridge structure supported by two vertical columns. The probe moves along the X, Y, and Z axes to accurately measure the dimensions and geometry of a workpiece. and placed on the table.
Construction Built on a precision granite surface plate for high rigidity and thermal stability. Two vertical uprights support the horizontal bridge (X-axis beam). The measuring probe moves in three mutually perpendicular directions: X-axis: Horizontal movement of the bridge or carriage. Y-axis: Movement of the table or bridge depending on configuration. Z-axis: Vertical movement of the probe. About 95% of bridge CMMs use air bearings, providing friction-free motion, smooth movement, and minimal mechanical wear. Working Principle The workpiece is placed on the granite table. The probe moves along the X, Y, and Z axes. When the probe touches the workpiece, the machine records the coordinates. Thousands of coordinate points are collected. The software analyses these points to determine dimensions, form, position, and geometric tolerances.
Features Most popular and widely used CMM configuration. Excellent accuracy, repeatability, and stability. Available in various sizes and accuracy grades. Suitable for inspecting small to medium-sized precision components. Advantages Very high measurement accuracy. Excellent repeatability over long periods. Rigid bridge structure minimizes vibration. Air bearings provide smooth and friction-free motion. Easy to relocate within a factory after proper calibration. Disadvantages Limited accessibility because the bridge uprights restrict access to the workpiece. Heavy components must be lifted onto the granite table using cranes or forklifts. Loading large workpieces may increase the risk of accidental collision with the machine. Not ideal for extremely large or very heavy components.
• Gantry CMM • A Gantry Type Coordinate Measuring Machine (Gantry CMM) is a large-scale version of the Bridge CMM designed for measuring very large, heavy, and bulky components with high precision. Unlike bridge CMMs, the workpiece remains on the factory floor while the gantry structure moves over it, eliminating the need to lift heavy components. Construction •Mounted directly on a rigid factory floor foundation. •Consists of four, six, or more vertical columns supporting large horizontal beams. •The X-axis carriage moves along the horizontal beams. •The Z-axis probe moves vertically and may have a travel of 1.2–4 m. •Measuring ranges typically vary from: • 1 × 2 × 1 m • Up to 4 × 10 × 3 m • Larger sizes are available for special applications.
Working Principle Large workpieces are placed directly on the shop floor. The gantry structure moves over the component. The probe travels along the X, Y, and Z axes. Coordinates of the workpiece are recorded. Computer software creates a precise 3D model and performs dimensional analysis. Features Designed for very large and heavy components. Floor-mounted with a dedicated rigid foundation. Excellent structural rigidity and stability. Large measuring volume. Easy access around the workpiece. Highly accurate despite large measuring ranges. Suitable for both contact and non-contact probes.
• Advantages Ideal for large and heavy workpieces. Components can be loaded directly using overhead cranes. No need to lift heavy parts onto a measuring table. Easy access for programmers and operators during inspection. Measurement process can be observed from all sides. Surface plates for smaller components can also be placed inside the gantry. High accuracy and repeatability over large measuring volumes. Suitable for shop-floor inspection. Disadvantages Requires a large installation area. High initial investment cost. Expensive foundation construction. Difficult to relocate after installation. Permanent installation in most factories. Higher maintenance cost than smaller CMMs. Applications Aerospace industry (aircraft structures, wings,) Automotive industry (vehicle body, chassis, ) Shipbuilding industry Heavy engineering components Die and mould inspection
Advantages Portable and easy to carry. Measures large and fixed workpieces. Reduces inspection time. Suitable for on-site measurement. Easy to set up and operate. Improves productivity. Supports CAD comparison and reverse engineering. Disadvantages Lower accuracy than fixed CMMs. Accuracy depends on the operator. Sensitive to vibration and temperature changes. Requires regular calibration. Limited measuring range for some types. Advanced systems are expensive. Applications Automotive component inspection. Aerospace component measurement. Tool and die inspection. Heavy engineering and large machinery. Reverse engineering. Manufacturing quality control. Railway and shipbuilding industries. Maintenance and repair (MRO).
Portable CMM A Portable Coordinate Measuring Machine (Portable CMM) is a lightweight, movable measuring system used to inspect the dimensions and geometry of components directly on the shop floor, production line, or at the installation site. Unlike conventional fixed CMMs, portable CMMs can be transported to the workpiece, making them ideal for measuring large, heavy, or immovable parts. • Working Principle • The portable CMM is positioned near the workpiece. • The operator moves the probe or scanner to the required measurement points. • The system continuously records the X, Y, and Z coordinates of each point. • The software converts these coordinates into dimensions, geometric tolerances, and 3D models. • Results are instantly compared with the CAD model or engineering drawing.
Types of probes including touch trigger, scanning and optical probes • The probe is the main sensing element of a Coordinate Measuring Machine (CMM). It detects the position of points on the workpiece surface and sends coordinate data to the computer for dimensional measurement. • A probe is usually mounted on the machine's Z-axis (quill) and comes into contact with the workpiece during measurement.
Probe Assembly • A probe assembly consists of the following components: • Probe Head – Connects the probe to the machine quill and allows positioning. • Probe – The sensing element that detects the workpiece surface. • Stylus – The tip that comes into contact with the workpiece. Probe Touch Trigger Touch → Stop → Measure Scanning Touch → Move → Measure Continuously Optical No Touch → Light/Camera → Measure
Touch Trigger Probe A Touch Trigger Probe is a contact-type probe that records the coordinates of a point only when the stylus touches the workpiece. Each contact generates an electrical signal that is sent to the CMM controller for measurement. Working Principle The stylus moves towards the workpiece. The stylus touches the surface. Internal sensors detect the contact. An electrical trigger signal is generated. The CMM stores the X, Y, and Z coordinates. The probe moves to the next point. Applications •Hole diameter measurement •Slot inspection •Boss and pin measurement •Flatness inspection
• Analog Scanning Probe (Scanning Probe) An Analog Scanning Probe is a contact probe that maintains continuous contact with the workpiece while moving over its surface. Unlike a touch trigger probe, it collects thousands of measurement points continuously. Working Principle • The stylus contacts the workpiece. • The probe moves continuously along the surface. • It records coordinates continuously. • A complete surface profile is generated. Applications •Turbine blades •Camshafts •Crankshafts •Automobile body panels •Sheet metal parts
Optical (Non-Contact) Probes An Optical Probe is a non-contact probe that measures the workpiece without physical contact. It uses laser light or a vision (camera) system, making it suitable for delicate, small, and complex components. Laser Probe Working Principle A focused laser beam is projected onto the workpiece. The reflected light is received by a sensor. The position is calculated using the triangulation principle. The CMM computes the coordinates Applications Plastic parts Rubber components Thin sheet metal Reverse engineering Surface profile measurement .
Vision-Based Probe Working Principle Uses a high-definition camera instead of a stylus. Captures images of the component. Software measures dimensions by processing the image (pixel analysis). Can generate multiple measurement points in one image frame. Applications Electronic components Printed circuit boards (PCB) Micro-components Medical devices Precision miniature parts
Applications in reverse engineering and inspection
• Reverse Engineering is the process of creating a 3D CAD model from an existing physical component when the original engineering drawing or CAD file is not available. • The CMM measures thousands of points on the component surface. These points are converted into a point cloud, which is then used to create an accurate CAD model. This CAD model can be modified, analyzed, or used for manufacturing a new component. • Applications of Reverse Engineering Legacy Part Reproduction • Many industries use old machines whose spare parts are no longer available. A CMM measures the existing worn part and creates a CAD model to manufacture an identical replacement. •Design improvement and optimization. •Tool and mould manufacturing. •Product development. • A worn textile machine cam is scanned using a CMM. The measured data is converted into a CAD model, which is used to manufacture a new cam using CNC machining.
Inspection is the process of checking whether the manufactured component matches the dimensions,. Applications of Inspection 1. Dimensional Verification The CMM measures: Length Diameter Hole location Distance between holes Flatness Perpendicularity 2. First Article Inspection (FAI) The first manufactured component produced from a new production line is inspected to ensure that it meets all design requirements before mass production begins. 3. Quality Control Practical Example (Inspection) Example: Gearbox Cover Plate for a Rotavator A newly manufactured gearbox cover plate is inspected before assembly. Working: The cover plate is placed on a bridge-type CMM. A touch-trigger probe measures: Bolt hole locations, Centre distances, Flatness of the mounting surface, Overall dimensions The measured values are automatically compared with the CAD model. The software generates a colour-coded deviation map: Green → Within tolerance Yellow → Slight deviation Red → Out of tolerance Result: Any warping, shrinkage, or dimensional error is detected before assembly, reducing rejection and improving product quality.