Automating metrology

Automation in manufacturing is not new. Control systems and information technologies have been used for decades to reduce the need for human input or interaction. Automated metrology systems have penetrated every aspect of today’s manufacturing process. During the past 40 years, programmable coordinate measuring machines (CMMs) with direct computer control (DCC) have replaced manual versions and manual inspection processes. These systems were once primarily used to audit the manufacturing process or complete final inspections in quality laboratories.

Today, an emerging trend in the automation paradigm is to incorporate metrology solutions for absolute measurement and inspection on the factory floor. By automating the inspection task and placing it on the shop floor near the point of production, companies can benefit from higher repeatability in their inspection process, increased inspection frequencies, and faster response back into the process through a variety of techniques including direct machine tool feedback.

Outside the world of the CMM, a wide variety of contact and non-contact sensor technology is being combined with numerous motion control frames to create similar advanced, in-process, absolute measurement cells. These sensors are also being combined with manufacturing processes to create an on-machine, metrology enabled, feedback control loop. Robotic in-process measurement and metrology-guided manufacturing and assembly are replacing costly, inflexible tooling.

Using these technologies lowers operating costs, supports consistent throughput, improves lean manufacturing capabilities, and improves product quality. However, an automated system is not a panacea for every manufacturing process nor should automation be considered to replace all human input and interaction. Careful consideration should be given to the application to see if and what level of metrology automation is a good fit.
 

When it makes sense

Automation makes sense in any area with time consuming, labor intensive, and repetitive activities. The danger is in believing that all of these activities could and should be automated without carefully looking at each aspect of the process. Highly complex activities are generally more costly and have considerably less return on investment. They also create a long-term requirement for high-end engineering talent for maintenance and troubleshooting. Advancements in software and hardware connectivity continue to push this boundary, but some tasks do not have the necessary value when replaced with automation.

Automation is not necessarily confined to loading and unloading parts off a machine. Look beyond the hardware within a manufacturing cell at processes that show potential for automation. Repetitive data analysis is one area where a company could automate and see immediate results. Coordinate data gathered from the production line can be immediately processed, analyzed, and disseminated throughout the organization, and used for further hardware automation. For example, a cell with EDMs may be automated without the need for robots. A CMM may be programmed to feed offsets and spark gaps to the machine if the data collection process has been automated.
 

Roadblocks to metrology automation

Although increasing in popularity, automating hardware has limits. Common automated manufacturing systems employ robotic equipment to facilitate part handling. In certain scenarios, such as lights-out manufacturing, fully automated machining cells incorporating metrology tools are the most efficient solutions to improve throughput. However, in some applications, a semi-automated solution incorporating automated and manual processes maximizes throughput. With these systems, a company needs to carefully consider when they make sense, when they do not, and the associated risks and rewards.

Technical limitations in both software and hardware for in-process and shop floor absolute metrology solutions still exist. Environmental conditions, including temperature, vibration, humidity, and cleanliness are often constraining. Integrating a high-precision CMM on the shop floor, for instance, is typically not feasible due to vibrations and temperature fluctuations. After machining, a part may have metal chips and oily residue on its surface. Components in this condition cannot be accurately measured and may damage the measurement device after repeated inspections.

Another limitation may be the cycle time of the manufacturing cell. Longer cycle times lend themselves to a manual or semi-automated solution. For example, a parts handling system is difficult to justify if the robots will only move four times per hour. Additionally, if a cell can manufacture parts in less time than it takes the metrology equipment to inspect them, a parts buffer may be needed to hold the waiting components.

Financial considerations come into play as well. Though many expect a high initial cost, they might neglect to factor in all potential expenses. For example, manufacturers might need enclosures and parts buffers. There could be costs associated with the lack of turnkey software solutions since no standard code exists for communication between the robotics and the CMM. Other important considerations are the lack of experienced personnel to implement the system and the associated integration costs.
 

Semi-automated systems

For some applications, a semi-automated system may be the most cost-efficient and productive solution. The goal for manufacturers is not to completely automate their facilities, but rather to maximize throughput within their application’s parameters. Instead of focusing strictly on automation, a more achievable objective would be to minimize capital expenditures. For example, a manufacturer could run efficiently with two CMMs instead of three. Labor is another cost consideration when deciding between a fully or semi-automated parts handling and inspection system. A company might think it is best to eliminate five low salary positions, but realistically it may need to hire three high salary employees to program, implement, and maintain such a high-tech system.

Though a semi-automated system may require a high level of human intervention, it could be the best solution for the application. Take for example a carousel with four pallets of parts that are automatically loaded into the CMM. Although a person must affix parts onto the carousel, a constant supply of components is ready for inspection. If the CMM operator is required to tend to other tasks, the parts will not sit idle.
 

Other automation options

Incorporating a CMM into a manufacturing cell is only one scenario of an automated inspection system. An array of solutions is available for metrology-assisted operations. Laser trackers integrated with robots are used to inspect, align, and assemble large aerospace parts. Stereovision systems are another viable alternative used to capture part data for large-scale measurement applications. These two non-contact measurement systems are not affected by vibration and dust in shop floor environments.

For those considering an automated parts handling system with integrated inspection, the final decision will be based on the application’s specifications. Some of the initial considerations include the required accuracy, the complexity of the parts, the ability to clean the parts before they are measured, and the preferred technology. Knowing these key points ahead of time will help frame the discussions and facilitate the overall integration process.

Hexagon Metrology
www.hexagonmetrology.us

About the author: Scott Everling is in charge of product/business development, Custom Solutions Group, Hexagon Metrology and can be reached at scott.everling@hexagonmetrology.com or 401.886.2121.