An eye for measurement
Comments Off November 19, 2010 at 11:36 am by Jill Nelson
We ask Applied Precision’s Scott Reiner about developments in laser and optical measurement
Applied Precision helped a manufacturer of goalie masks, one of which is pictured here, using one of its laser scanners.
Is laser measurement the only type of optical measurement for quality control?
Scott Reiner: Laser is one type of optical measurement for quality control in the manufacturing environment. Other devices that optically measure data points like lasers are white light scanners (fringe projection), which collect high density organized point cloud files, and photogrammetry systems, which measure individual data points on objects with the use of digital cameras. These systems can be used independently or together to achieve high density data on larger objects. Photogrammetry systems are single point measurement systems similar to a CMM however the points collected are referenced on the object being measured by reflective targets. These targets create individual X, Y and Z points in space. These reference targets can be measured by the white light systems to align their high density scan shots to the previously created 3D reference file. The procedure is useful for measuring high density data on the front and back of a car when the user is not concerned with what is in between the two or more areas, or when high accuracy is required on medium or larger objects.
What have been the top three developments in laser measurement devices for manufacturing in the past five years?
SR: The three main developments for short to medium range laser scanners include better camera chip and lens technology advancements offering better resolution of data collection on small details on objects. Steinbichler has excelled at this with the new lens technology on the Comet 5 11M offering resolution down to 18 microns for point to point/data density. Improved calibration techniques have helped achieve better accuracy of each point collected by calibrating the extents of the volume and high end math calculations of the scanners. Signal processing improvements have allowed for better adaptive readings from different surface finishes such as mirror like and shiny black.
What are the key benefits of laser measurement in manufacturing?
SR: Laser measurement offers fast, accurate, complete 3D data collection on complex geometry, compared to the slow single point typical of a granite based CMM. Laser measurement also offers the added advantage of typically being much more portable, which means that you can measure the part on the machine rather than moving the part to the CMM and back if corrections need to be made on the machining equipment. This optical data collection is useful for inspection or CAD model updating when changes are made manually on the shop floor to make parts or tools work for a given application, such as a stamping die with spring back compensation that is beyond what was originally designed into the tool.
What are the different types of laser measurement technologies used in manufacturing and how do they compare?
SR: There are many types of measurement technologies including laser trackers, short-medium range laser scanners (line or dot), long range laser scanners and fringe projection laser scanners to name a few. Each technology is suited to a specific type of measurement; there are no “silver bullets” for laser measurement systems where one system will cover all applications that an organization requires. Most companies try to purchase the system that suits 80 to 90 per cent of their applications. Laser trackers are typically a single point measurement system used on large objects that require accuracy in their inspection as well as having the added advantage of offering in-process inspection where the part can be inspected on the machine before being removed, allowing confirmation that the part is correct before removing it from the machine. These systems are also now being offered with laser scanners to expand the functionality of the measurement tool.
How does measuring part tolerance/specs with lasers compare to other forms of measurement?
SR: While a CMM in a climate controlled room would offer the most repeatable and most accurate results, comparing this with a laser tracker on the shop floor during the summer or winter with the door open in the shop the temperature expansion or contraction would need to be taken into account for shop floor measurements. Portable laser measurement systems would depend on the type of system utilized and some can be temperature calibrated in the environment that they are going to be used. The general rule of thumb for measurement is to utilize a measurement device that is capable of 10 to 20 per cent of the accuracy requirements of the part to be measured, with increased tolerance capabilities of manufacturing processes. This rule of thumb is modified in some cases as the additional amount of data collected through scanner type collection units offers more data density for quality personnel to understand better what is happening with a part versus single point measurement.
Is laser technology for measurement used in small and medium sized manufacturing companies or is this technology typically adopted more by larger firms?
SR: Yes, optical measurement technologies are growing in adoption. As the technology gets more accurate and easier to use, the size of the company is not seen
as a limiting factor of adoption. Specific measurement needs by a company are a larger driver of adoption and if the need is there, the cost is typically justifiable.
What key factors will influence future developments in laser measurement?
SR: For systems to evolve, the demand needs to be there to motivate improvements, as technology companies typically design products only to meet the needs of customer requests. However, the ROI can also drive advancements for the manufacturer. If you compare the technology in a Bugatti Veyron with that of a Chevrolet Volt both are impressive pieces of current automotive technology but the price is different based on the market that each is selling to as well as what each vehicle is capable of: one can go 400 km/h and the other can go 40 miles on a single electric charge. The current state of technology answers most current needs, albeit sometimes with multiple solutions for any given customer measurement requirement. It will be a long time before we see a car that is capable of 400km/h on a single electric charge.
What key changes do you foresee in laser measurement systems for manufacturing?
SR: Most changes in optical measurement will be flexibility, where a single system will be able to do multiple types of measurements, like a laser tracker being able to scan an object’s surface as a long range scanner does and vice versa. Another key change will be increased accuracy in tracking methods for small to medium range systems as well as in-field verification and calibration of the scanners for those that can’t currently. QC
Scott Reiner is the vice president of sales and marketing, Applied Precision Inc., Mississauga, ON.