Probing glossary and terminology

What is a probe?

Probing is traditionally associated with contact probes used for dimensional measurement (metrology) on co-ordinate measuring machines (CMMs).

The first application of the original contact probe was in solving complex dimensional QA problems for the Rolls Royce Olympus engines used on Concorde.

A probe is effectively an elaborate switch, designed to trigger on contact with a component surface, providing accurate, repeatable geometric data. Obtaining and interrogating this data throughout the manufacturing process can help to ensure components remain within conformance limits.

Accurate - deviating only slightly or within acceptable limits from a standard.

Precise (repeatable) - exact, as in performance, execution, or amount: accurate or correct.

For more information on probe technology, see the Further reading section, or
(TE411) Innovations in touch trigger probe sensor technology.

Work piece/inspection probe technology

Renishaw's inspection probes are referred to as either kinematic resistive or strain gauge, the latter incorporating patented RENGAGE™ technology.

Kinematic resistive probes

Kinematic resistive probes incorporate a spring loaded kinematic mounting arrangement of rods and balls to position the stylus holder, providing excellent repeatability.

An electrical circuit provides resistance. As force on the stylus increases so does the resistance until a trigger threshold is reached and a trigger signal is generated.

Capabilities

• 1 µm 2σ repeatability derived from fundamental kinematic resistive electrical switch
• Comprehensive size and wireless transmission options
• Industry standard, robust, ‘all-round' products

RENGAGE™ strain gauge probes

Strain gauge probes retain the kinematic mounting arrangement of kinematic resistive probes, but utilise a series of strain gauges to measure contact force on the stylus and generate a trigger signal.

Capabilities

• Best-in-class 0.25 µm 2σ repeatability
• Sub-μm 2D and 3D pre-travel variation
• Solid-state sensing gives robustness and extended life
• Active false trigger filtering
• Rapid multi-axis re-orientations
• Suitable for use with long styli

For more information on probe technology, see the Further reading section, or
(TE411) Innovations in touch trigger probe sensor technology.

Tool setting technology

Tool setting is the process of determining geometric information - such as length, radius, and/or diameter of a cutting tool using a tool setting device and dedicated software. Devices are classified as either contact or non-contact tool setters.

Contact tool setters

Contact tool setting systems require physical contact between the device and the loaded tool. Systems can be further classified as 'plunger' style, 'probe' style or tool setting arm (used for turning centres).

Advantages

• Repeatability and tool-to-tool accuracy
• Robust in machine environments
• Cost-effective
• Measures in different spindle orientations
• Optical transmission available
• Measures diameter of rotating tools as well as length

Considerations

• Can deflect very small tools
• No complex edge checking
• Usually mounted on the table

Non-contact tool setters

Non-contact tool setting systems employ an optical (laser) beam to detect tool presence. Systems can be sub-divided as 'fixed' systems (transmitter and receiver units housed within a single assembly), or 'separate' with individual transmitter and receiver assemblies.

Non-contact systems can also check for breaks and/or chips on a tool's cutting edge.

Advantages

• Will not deflect very small tools
• Measures at high spindle speeds
• Permanently protected optics
• Edge checking detects chipped flutes and inserts
• Multiple measuring points possible

Considerations

• Generally more expensive than contact systems
• Installation more complex: clean air supply required
• Harsh environments and debris can cause application problems and measurement errors with all optical sensors
• Not suitable for fixed tooling

ToolWise™ tool recognition system (broken tool detection)

Broken tool detection is the process used to determine tool condition information such as radial and linear profile and cutting edge condition and is available as a function of most tool setting devices as well as via dedicated tool detection systems. 

Capabilities

• Ultra quick detection times using unique ToolWise™ pattern recognition capabilities
• Flexible system capable of operating over a wide range of tool rotation speeds (200 rpm to 5000 rpm)
• Simple set-up mounted out of the working envelope of the machine

For more information on tool setting technology, see the Further reading section, or
(TE500) Tool setting and broken tool detection

(TE511) Renishaw's non-contact laser tool setting technology

(TE512) Unique 'tool recognition system' detects broken tools with ease

Probe transmission technology

Optical and radio transmission

Optical transmission systems

Optical transmission systems use infra-red light to transmit information between the probe and the interface/controller. Renishaw systems incorporate modular transmission technology to reduce interference from external sources.

Optical systems require a clear 'line-of-sight' between probe and receiver, meaning they are most suited to small/medium machines without complex fixturing.

Typical achievable transmission distance is 6 m.

Radio transmission systems

Radio systems use radio waves to transmit signals from the probe to the interface unit. Transmission from Renishaw systems 'hops' between channels within a designated frequency band to avoid interference from surrounding devices, and incorporates unique identifiers allowing multiple systems to operate in close proximity of one another. Classified as short range devices, Renishaw radio probes meet the requirements for licence-free operation.

Radio systems do not have the 'line-of-sight' requirements of optical systems, making them ideal for 5-axis machining centres and large machines with complex fixturing assemblies.

Typical achievable tranmission distance is 15 m.

For more information on radio transmission, see the Further reading section, or
(TE421) Frequency hopping spread spectrum (FHSS) radio transmission