1	CMM Inspection Fundamentals Factors that affect CMM measurement performance and the selection of probing solutions
2	Which Inspection Solution Will Suit Your Application?
3	Probing Applications – Factors (1) Manufacturing demands a range of measurement solutions. Why? Machining processes have different levels of stability: Stable Form : therefore control size and position -> Discrete point measurement Form Variation is Significant : therefore form must be measured and controlled -> Scanning
4	Probing Applications – Factors (2) Manufacturing demands a range of measurement solutions. Why? Features have different functions: for Clearance or Location form is not important -> Discrete point measurement for Functional Fits form is critical and must be controlled -> Scanning
5	Discrete Point Measurement (1) Ideal for controlling the position or size of clearance and location features Data capture rates of 1 or 2 points per second Avoids stylus wear Touch-Trigger Probes are ideal lower cost, small size and great versatility Scanning Probes can also be used Passive Probes can probe quickly Active Probes are slower because the probe must settle at a target force before taking the point
6	Discrete Point Measurement (2) Speed comparison
7	Scanning (1) Ideal for controlling the Form or Profile of known features that form functional fits with other parts Data capture speeds of up to 500 points per second Incurs wear on the stylus Scanning allows you to: Determine the feature Position Accurately measure the feature Size Identify errors in the Form or shape of the feature
8	Scanning (2) Scanning a cylinder block
9	Digitising (1) Ideal for capturing large amounts of data about an unknown surface Uses many of the same techniques as scanning Deflection vector of the probe is used to determine the motion vector in which the machine moves next Digitised surface data can be: Exported to CAD for reverse engineering Used to generate a CNC program for re-manufacture
10	Digitising (2) Re-manufacture and Reverse Engineering
11	Which Inspection Solution Will Suit Your Application?
12	Measurement Applications Measurement of size, position and form of precision geometric features Measurement of profiles and complex surfaces
13	Speed and Accuracy High speed data capture - up to 500 points per second Large volume of data gives an understanding of form High point density gives greater datum stability Dynamic effects due to accelerations during measurement must be compensated if high speed scans are to produce accurate measurement results. CMM stiffness critical
14	Complexity and Cost
15	Flexibility
16	The Ideal Scanning System Characteristics of the ideal scanning system: High Speed, Accurate Scanning of the form of known and unknown parts Rapid Discrete Point Measurement when measuring feature position Flexible Access to the component to allow rapid measurement of all critical features on the part Easy Interchange with other types of sensor, including touch-trigger probes and non-contact sensors. Allows the sensor choice for each measurement to be optimised Minimum stylus wear
17	Which Inspection Solution Will Suit Your Application?
18	Dynamic Effects on Scanning Performance (1) The Scanning Paradox… Modern CMMs can move quickly, yet conventional scanning is typically performed at low speeds less than 15 mm sec (0.6 in/sec) Why?
19	Dynamic Effects on Scanning Performance (2) Scanning Induces Dynamic Forces in the structure of the CMM and the probe itself, which will negatively affect measurement accuracy Dynamic Errors are Related to Acceleration of the machine and probe as the stylus is moved over the surface of the component Accurate Scanning requires a Stiff CMM
20	How Do CMM Dynamic Errors Occur? (1) Discrete Point Measurement is done at constant velocity - acceleration is zero at the point of contact with critical damping Consequently there are No Inertial Forces on the machine or probe
21	How Do CMM Dynamic Errors Occur? (2) Scanning requires continuously changing velocity vectors as the stylus moves across the part curved surface Varying Inertial Forces are induced, which cause the CMM frame to deflect Vibration can also a factor when scanning Accurate Scanning requires a Stiff CMM
22	What About Scanning Sensor Dynamics? During scanning, the deflection of the probe varies due to the difference between the nominal programmed path and the actual surface contour The probe must accommodate rapid changes in deflection, without loss of accuracy or leaving the part surface The ideal scanning sensor can accommodate a rapidly changing profile due to: a high natural frequency low suspended mass low overall weight
23	Dynamic Errors in Practice (1) Example 1: Measure a Ø50 mm Ring Gauge at 10 mm/sec (0.4 in/sec) using a CMM with performance of 2.5 + L/250 (2.5 + microns)
24	Dynamic Errors in Practice (2) Example 2: Measure the same Ring Gauge at 100 mm/sec (4 in/sec) on the same (2.5 + microns) CMM
25	The Dynamic Performance Barrier (1) Dynamic errors increase as CMM speed rise
26	The Dynamic Performance Barrier (2) Scanning speeds have to be kept low if tight tolerance features are to be inspected
27	Which Inspection Solution Will Suit Your Application?
28	Articulated or Fixed Sensors? Articulated Heads are a standard feature on the majority of CNC CMMs Heads are the most cost-effective way to measure complex parts Fixed Heads and Probes are best suited to applications where simple parts are to be measured Ideal for flat parts where a single stylus can access all features
29	Articulated Heads – Benefits (1) Flexibility - a single, simple stylus can access features in many orientations Indexing and continuously variable solutions 7.5 degree index is proven to offer maximum flexibility while optimizing calibration times
30	Articulated Heads – Benefits (2)
31	Articulated Heads - Repeatability Indexing repeatability affects the measured position of features Size and form are unaffected Most features relationships are measured ‘in a plane’ Feature positions are defined relative to datum features in the same plane (i.e. the same index position) Datum feature used to establish a part co-ordinate system Therefore indexing repeatability typically has no impact on measurement results, but many benefits
32	Articulated Heads – Benefits (3) Speed - Indexing is faster than stylus changing (done during CMM moves) Dynamic Response - simple, light styli make for a lower suspended mass Costs Simple styli with low replacement costs Small, low cost stylus change racks
33	PH10M Indexing Head - Design Characteristics Flexible Part Access
34	Articulated Heads – Benefits (4) Automation - Programmable probe changing with no manual intervention required Touch-probe, scanning and optical probing on the same machine Stylus Changing - even greater flexibility and automation Optimise stylus choice for each measurement task
35	Articulated Heads - Disadvantages Space - A head reduces available Z travel by a small amount - can be an issue only on very small CMMs
36	Fixed Sensors - Benefits Compact - Reduced Z dimension makes minimal intrusion into the measuring volume - ideal for small CMMs Simplicity - Fixed passive sensors are less complex for lower system costs Note: An Active sensor is more complex and often more expensive than a passive sensor and an articulating head combined
37	Fixed Sensors – Disadvantages (1) Feature Access - Large and complex stylus arrangements are needed to access all part features
38	Fixed Sensors – Disadvantages (2) Programming Complexity - Complex stylus clusters mean more attention must be paid to collision avoidance
39	Fixed Sensors – Disadvantages (3) Machine Size Large stylus clusters consume measuring volume Much larger stylus change racks consume more space You may need a larger machine to measure your parts
40	Fixed Sensors – Disadvantages (4) Speed - Stylus changing takes longer than indexing Up to 10 times slower than indexing Indexing can be done during positioning moves Dynamic Response - Heavy styli increases suspended mass and limits scanning speed even more Accuracy - Complex styli will compromise metrology performance
41	Which Inspection Solution Will Suit Your Application?
42	Why Change Styli? Optimise Your Measurement Repeatability For each feature by selecting a stylus with: Minimum length Longer styli degrade repeatability Maximum stiffness Minimum joints Maximum ball size Maximise the effective working length (EWL)
43	Stylus Changing Many probe systems now feature a Repeatable Stylus Module Changer Access to features that demand long or complex styli Different tips (sphere, disc, cylinder) needed for special features Automated stylus changing allows a whole part to be measured with a single CMM programme Reduced operator intervention Increased throughput
44	SP600 Stylus Changing Stylus Changing
45	Why Change Probes? Not all parts can be measured with one Probe:
46	Probe Changing The Requirement... If the range of features and parts that you must measure demands a range of sensors, then a Probe Changing System is essential
47	ACR3 Probe Changer for use with PH10M Probe Changing
48	Which Inspection Solution Will Suit Your Application?
49	Passive Sensors – Renishaw Patented Technology Simple, Compact Mechanism No motor drives No locking mechanism No tare system No electromagnets No electronic damping Springs generate contact force Force varies with deflection
50	Active Sensors – Renishaw Competitors Complex, Larger Mechanism Force generators in each axis Force is modulated but not constant Deflection varies as necessary Longer axis travels
51	Scanning A ‘Defined’ Surface Most Scanning is Performed on ‘Known’ or ‘Defined’ Features Feature size, position and form vary only within manufacturing and fixturing tolerances
52	Scanning Sensor Design Factors Passive Sensors Contact force is controlled by CMM motor drive Compact sensor that can be mounted on an articulating head Short, light, simple styli Low spring rates
53	Scanning Probe Calibration (1) Passive Sensors Probe characteristics, including stylus bending, are calibrated Simple calibration cycle Sophisticated non-linear compensation
54	Scanning Probe Calibration (2) Constant force does not equal constant stylus deflection Although active sensors provide constant contact force, stylus bending varies, depending on the contact vector Stylus stiffness is very different in Z direction (compression) to in the XY plane (bending) If you are scanning in 3 dimensions (i.e. not just in the XY plane), this is important e.g. valve seats e.g. gears
55	Scanning Probe Calibration (3) \ constant force does not result in better accuracy how the probe is calibrated is what counts
56	Active or Passive Scanning - Conclusion Both active and passive systems achieve the basics - accurate scanning within their calibrated operating range Their performance and costs differ Look at the specification and complexity of the system before making the choice Cost of ownership also make should a huge difference in your decision
57	Questions Yo Ask Your CMM Supplier Do my measurement applications require a scanning solution? Which parts need to be scanned? Which parts can be discrete point measured? If I need to scan, what is the performance of the system? Scanning accuracy at high speeds Total measurement cycle time, including stylus changes and styli calibration If I also need to measure discrete points, how fast can I do this with a scanning probe?
58	Questions Yo Ask Your CMM Supplier Will I benefit from the flexibility of an articulated head? Access to the component Sensor and stylus changing What are the lifetime costs? Purchase price What are the likely failure modes and what protection is provided? Repair / replacement costs and speed of service – Renishaw RBE (Repair by Exchange Program) is the best, fastest and cheapest in the industry and Renishaw probe replacement is plug and play – no CMM service technician necessary
59	You have Questions?