Shop Measurement

In-process measuring, five-axis capability, and laser scanning can all provide benefits when implemented correctly

February 1, 2011

New measuring technologies for the shop.

During manufacturing as well as immediately following machine work, parts must be measured to ensure that the proper quality is met. This means that a company’s measurement and metrology department is an important hub of activity.

However, as technology evolves, this department no longer needs to be the clean-room of the past. Now measuring also can be done directly on the shop floor. Three methods for doing this are laser tracking, five-axis measuring, and in-process measuring.

Laser Tracking

The use of portable, 3-D measurement and imaging systems continue to increase, however, harsh shop environments can reduce these device’s lifespan and reliability.

To address this concern, FARO Technologies recently expanded its line of laser trackers with a new spherically mounted retroreflector (SMR) that is extremely durable, the company reports.

According to FARO, the device’s accuracy is equal to or better than a traditional glass-panel SMR, while having the added advantage of being break-resistant.

These new targets are available in three models: standard accuracy, long range, and high performance. Each one has higher accuracy than previous break-resistant SMRs from the company, and the long-range and high-performance models have the ability to track up to 55 m.

“Regardless of how accurate your laser tracker is, the quality of the measurements is directly affected by the precision of the target,” said Ken Steffey, FARO director of product management – Laser Tracker products. “These new break-resistant SMRs contain a single element retroreflector with a gold coating. Since the retroreflector is constructed of a single element, there are no separate glass panels that can shift or break over time.”

The company also has introduced its new line of patented, break-resistant, window SMRs. The window covering has been designed to keep the reflective optics clean.

Five-axis Measurement

Coordinate measuring machine (CMM) inspection throughput can be increased threefold by using five-axis rotary positioning and “head touch” capability for high-speed point capture with minimal CMM movement, says manufacturer Renishaw.

The company’s new PH20 head, which is used with the TP20 touch-trigger probe, can perform five-axis inspection in small CMMs for the first time by optimizing the working volume of the measurement platform. The head is available for new CMMs, as well as retrofit machines using shank or quill mounting. The head can use most existing inspection programs for indexing heads without modification and requires no compressed air.

“The PH20 is significant because it makes five-axis inspection practical and accessible for almost all CMMs,” explained Renishaw’s U.S. National Sales Manager Denis Zayia. “Unlike conventional touch-trigger measurement, which relies on speeding up the movement of the CMM’s three axes to measure quickly, [this model] uses head motion to minimize CMM movement, and the associated dynamic errors, at higher measurement speeds.”

The probe head saves measurement time by synchronizing its motion with the CMM between measurements. This “inferred calibration” technique determines head orientation and probe position in a single operation, allowing subsequent measurements at any head angle.

In-process Measurement

NC cylindrical and tool grinding machines often are equipped with a touch probe mounted on a tilting fixture in the machine workspace when tight workpiece tolerances are required to meet high process reliability. It is common to see touch probes used on surface grinders for in-process measurement of workpieces with long dimensions, for example, to ensure optimum process control. 

On lathes, touch probes commonly are used when workpieces have to be measured in small-batch production.  A touch probe also can be used to inspect turning tools for wear and breakage directly in the machine.

In-process measurement requires a touch probe with high repeatability and a high number of probing cycles.  Signal quality and trigger-point repeatability are key. 

According to manufacturer Heidenhain, the TS 249 touch probe can be used in both grinding machines and lathes.

This touch probe provides trigger signals that are ready for immediate processing by the control.  There is no need for an amplifier interface between the device and the control. 

For more information, visit www.faro.com, www.heidenhain.us, and www.renishaw.com.