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Benefits Of Improved Multisensor Measurement

Benefits Of Improved Multisensor Measurement

Multisensor systems have evolved considerably over the years as the component technologies for motion control, optics, lighting and cameras have improved. Tim Sladden, Quality Vision International, tells us more.

Multisensor coordinate measuring machines that combine vision, touch and laser sensors have been used in manufacturing quality control for nearly 20 years. Many still recall the early days of multisensor systems when the primary sensor worked well, but the additional sensors – sometimes added almost as an afterthought, offered limited capability and poor accuracy.

Today’s multisensor systems have advanced to the point that all sensors now offer full capability and accuracy. Limitations inherent in earlier designs have been removed through more careful integration of the sensors with the measuring axes.

Improvements in the metrology software are the greatest enabler of comprehensive multisensor capability. Measuring software has evolved in ways that allow each sensor to be truly integrated and measure with consistent uncertainty at all times.

Along the way the economic benefits of multisensor measurement systems have become clear: reduced capital and calibration expenses, shorter learning cycles, added flexibility and convenience, and most important – lower overall uncertainty in the measurements.

Figure 1

Manufacturing Processes Improved

To highlight the full range of capabilities of today’s multisensor measuring systems, let’s look at three types of parts and how their manufacturing processes have been improved by using multisensor measurement.

In Figure 1, we see a femoral implant being measured with a calliper. This is not that simple orthopaedic implants are among the most complex-shaped devices being machined today – there is simply no way to measure the critical dimensions and form of these parts with a single sensor system.

For starters, the highly polished surfaces of knee implants are extremely sensitive. Even casual contact by a tool or gauge could damage the surface finish, causing friction that could lead to improper fit and ultimately pain in the patient receiving the implant. To measure these parts, a variety of non-contact or minimally invasive tools – vision optics, lasers or very light contact probing force – are needed.

More importantly, femoral implants consist of a series of curves controlled by profile tolerances, each of which is simultaneously constrained by the material condition of one or more datum features. These geometric dimensioning and tolerancing (GD&T) conventions enable the designer to specify the form of the part exactly, but make verifying the part a challenge. To properly measure this part, the measurement points must be collected, and then fitted to the CAD model in their entirety in order to ensure all material conditions are properly evaluated. Data from tactile, scanning, laser and optical sensors needs to be integrated with the CAD model, and powerful software is needed to perform the GD&T evaluation.

Modern System

Enter the modern multisensor system. A system with telecentric optics, through-the-lens laser, and a micro-scanning probe can measure the outside dimensions, profiles and curves without damaging the part, and compare the data directly to the CAD model.

The manufacturer of this part faced high re-work and scrap rates, in spite of careful machining, polishing and measurement. Compounding the issue were disputes about dimensional conformance between different measurement techniques.

Multisensor measurement solved the first problem, by accurately measuring the critical features without damaging the part. True multisensor software enabled the data to be fitted to the CAD model and applied the GD&T standards properly.

This combination enabled the manufacturer to eliminate disputes about measurement accuracy between different gages, and ultimately reduce the number of finishing steps needed to produce the part to customer specs. All of which reduced scrap and re-work costs substantially.

Our next example is a large casting with a variety of machined surfaces, mounting holes and bearing ways on each of its four sides. This part has more than 50 discrete dimensions that must be controlled to ensure fit and function within the assembly it is part of. Many of these dimensions relate to datums on opposite or adjacent sides of the part. Ideally, the part would be measured in one set-up, without having to re-stage the part to enable measurement of all its surfaces.

While access and tolerance issues make a tactile scanning star probe (Figure 2) the ideal sensor for the bearing tracks, other features such as the small blind holes on the adjacent face are best measured using video, while surface flatness measurements on the mating surfaces are best made using a laser. The custom made flip fixture in this photo automatically indexes the part to present each side to the sensor array for measurement. This casting is a component in a complex assembly that relies on machined-in precision for the reliability of the overall mechanism. Thus, measurement is critical to the overall quality of the end-product.

For the maker of this part, multisensor measurement offered a number of benefits. Most significant was the time savings of being able to confirm all dimensions on one system, rather than having to program, stage and measure on several different systems, then combine and compare the data to determine if the part met spec. Another significant benefit is that the multisensor system offered the same uncertainty regardless of the sensor used.

In our third example, we see another complex machined casting – in this case, hydraulic transmission housing. This part presents a challenge to measure in a single set-up. Not only are there dimensions along the outer stems and top flange, there are dimensions on the seal surface and spline more than six inches deep inside the part. To access all these features in one orientation, long working distance optics and a LWD laser are needed to reach features at the bottom, as well as scanning probe capability to measure inside dimensions on the stems and interior profile.

Once again, the combination of scanning probe, laser and video measurement makes quick work of measuring this complex part. The laser quickly gathers a large pattern of data from the mating surface on the top flange. Flatness on this seal surface is critical. The scanning probe measures the interior profile in several locations, as well as the inside diameters of the in-flow and out-flow stems to calculate interior volume and flow rate characteristics. The long working distance laser also reaches to the boss on the inside of the spline for a flatness measurement, and long working distance optics quickly measure the gear teeth and ball bearing positions in the ball spline.

Each of these three examples illustrates the value inherent in a high quality multisensor measurement:

In all cases, it was possible to measure the entire part on one measuring system – saving the cost of buying and maintaining multiple measuring systems, and eliminating the differences in uncertainty between differing measurement technologies.

The range of sensors available enabled the key dimensions to be measured using the best sensor type for the feature without compromising efficiency or accuracy. Deployable and long working distance sensors help eliminate interference between sensors and minimise offsets that use up valuable measuring range.


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Automated Dimensional Metrology Improves Productivity

Automated Dimensional Metrology Improves Productivity

As machine tool technology continues to evolve, it is possible to create intricate, detailed parts from a wide range of materials. A critical part of a manufacturing process for such parts is verification that they comply with the specifications on their design drawings. With management focus on minimising costs and maximising throughput, manufacturers would want to avoid any bottlenecks from the measurement process. This is where use of CNC measuring systems that include automation of part handling can keep up with those demands. By Fred Mason, Senior Vice President of Marketing for Quality Vision International, the parent company of Optical Gaging Singapore Pte. Ltd.

No matter how accurate the tools are for making parts, their important dimensions need to be verified to ensure they meet quality expectations, so they will fit and function appropriately as parts of higher level assemblies. Numerous measurement technologies are used for quality control and process monitoring in today’s manufacturing environments. Automation of the inspection and measurement of the parts while in-process or post-process provides a number of benefits that relate to increased productivity across the supply chain.

No longer is it acceptable to have parts queued up outside a quality lab while production schedules are tight. Today manufacturers want to have the measurement process close to where the parts are being made. CNC measuring machines such as the OGP SmartScope range of multisensor metrology systems from Quality Vision International, automate the measurement of parts brought to the systems, which can be right in a work cell. In those environments the machinist who makes the parts measures them too. Simply load a batch of parts on to the measuring machine and press the start button. With a versatile multisensor measuring system, optical imaging, laser scanning, and touch probing can all be part of a single measurement process on a single machine. That range of technologies allows numerous features of various sizes and resolutions across any surfaces of the part to be measured without operator intervention. Any out of tolerance dimension is flagged for rapid, visual acceptance testing.

Many SmartScope systems are operated on multiple shifts measuring batches of parts loaded on and removed from the systems by their operators. Although measurement of those parts can be fully automatic once they are on the measuring machine, the overall throughput can be improved, and associated costs reduced using robotic and motorized pallet loading and unloading under program control.

There are numerous implementations of automation for part handling with automated measuring systems. In the simplest case a robot or cobot can be fitted with an end effector designed specifically for the part being measured. Individual parts can be picked up from a tray or box, moved to, and positioned on a measurement system. Programming of the robot can trigger the measuring system to initiate a measurement sequence as soon as it moves away from positioning the part. In addition, the measuring system can trigger the robot to return and pick up the part at the end of the measurement routine. Depending on the outcome of the measurement, acceptable parts can be placed or dropped into the “good” tray and out-of-tolerance parts can be placed or dropped into the “reject” or “rework” tray. In addition, a traffic light can signal that a measurement sequence is in process or completed.

Depending on the size and complexity of the part, it may not be necessary for the robot to place the part on the measuring machine, move aside, then return to pick up the part. An optical measuring machine with a large imaging area and telecentric optics, like the company’s SNAP systems, allow a robot to continue to hold the part while it is in the measuring area. The optical telecentricity ensures that part dimensions are imaged and measured accurately no matter where the part is within the system’s viewing area.

For CNC measuring systems where individual parts being measured are moved relative to each measuring sensor during a measurement sequence, it can be advantageous to automatically load pallets of parts at a time. Batches of parts can be placed on the measuring machine’s stage manually or by a motorized pallet loader. As with the example described above for a single part, insertion of a pallet can signal the measuring machine to initiate a routine, and completion of the measurement of the final part can signal the pallet loader to extract the pallet and insert the next one.

CNC measuring systems measure numerous features on complex parts without any user participation. Applying automated part loading and unloading can automate the front and back end of the overall measurement process, improving throughput and reducing operator to operator variability. The overall supply chain can see improved productivity from reduced costs and increased throughput with metrology automation.


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An Insight Into The Utilisation Of Measurement Sensors In Manufacturing Processes

An Insight Into The Utilisation Of Measurement Sensors In Manufacturing Processes

Manufactured parts need to be measured to ensure they meet the original design intent. Modern manufacturing techniques allow complex parts to be designed with numerous critical dimensions. A key element in precision metrology is having the right measurement tool for the job. Modern measurement machines use a variety of sensors to collect measurement data. Metrology software analyzes the measurement data, and through numerical and graphical reports, allows the user to make confident decisions about the part design and manufacturing processes. By Terry Herbeck, Vice-President of Asian Operations at OGP

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