With the resurgence of manufacturing in the United States has come a high demand for flexible quality inspection systems in the production environment. To keep up, CMM’s and other flexible measurement systems have had to get much faster without sacrificing accuracy. That has led the top manufacturers of metrology equipment to introduce high-speed machines capable of being placed directly on to the shop floor.
Many of these machines are used in an inline scenario, but many others are used “near line,” supporting multiple operations and products with a single inspection apparatus. While these technologies are being applied to vision and form measuring technology as well, for the purpose of this article we will focus mostly on CMMs.
As these next generation higher performance, high-technology machines begin to proliferate in the manufacturing environment, the need to address the safety concerns associated with them has been a critical factor in their implementation. The safety, while most importantly is concentrated on the personnel running it, also focuses on protecting the investment in these technologies from wayward participants.
There are several ways to approach this and many of them are factors of the environment in which they must withstand and the training level of the planned operator. With a “shop floor rated” CMM, the approach might be a simple safety mat, light curtain or zone/area sensor tied to the internal safety circuits of the machine.
In many cases it isn’t just the proximity, speed or environment that seals the decision in how the flexible inspection equipment is implemented; budgets sometime play a critical role in the approach one company takes compared to another. In many cases, a shop floor rated machine can be a substantial investment compared to a standard lab-grade machine, but adding a low-cost enclosure can sometimes meet the critical needs of the application without having a severe impact on one’s budget. In most cases, this is a simple aluminum extrusion based enclosure that can include lighting, air conditioning and interlocked doors to keep personnel out while the machine is in cycle. So depending on the route taken, the appropriate protection can then be decided by performing a thorough risk assessment. It is generally the role of the end user or integrator that performs these implementations on their behalf and there are many resources to assist in this process.
In other cases, it is the material being inspected that requires an additional level of capability. The ergonomics and safe handling of larger work pieces can be of serious concern. Many of these larger work pieces require the assistance of an overhead crane, forklift or other lifting devices. In these cases there is a need to add some type of shuttle or conveyance system that allows for the loading and unloading of the work piece outside of the machine volume. This not only helps the operator have better access to the loading/unloading operations, but it shields the machine from potential damage caused by a part that might get away from its handler.
As machines become more automated and connected to the Internet of Things (IoT), making these machines even more productive and efficient, the technology also allows machines to operate autonomously (or semi-autonomously) where workers may be near a non-running machine on the shop floor and then the machine turns on via program or through communications with surrounding support systems. This can happen remotely with little or no notice, creating even more potential for a hazardous condition if the protections were not put in place to prevent injuries.
A Closer Look at Accidents
In a series of investigations in Sweden and Japan, regulatory agencies discovered many accidents involving autonomous, or robotic type systems, did not occur during normal operating conditions. Instead, the majority of accidents happened during “programming, program touch-up or refinement, maintenance, repair, testing, setup or adjustment.” (https://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_4.html) This had led the lead agency here in the United States, OSHA, to develop strong standards on how these types of systems must be implemented in the workplace. CMMs now fall into the same category as robots, since in essence they use the same (CNC) technology to drive the motion, and in some cases can have the same speed and kinetic energy of them. The design criteria generally causes them to fall into the category of “Gantry” robots, though designs vary by manufacturer. This has forced many manufacturers to adjust their designs and even in some cases, slow the machines down or reduce the energy to below acceptable levels for injury.
When one or more of these machines are operating in-line, near-line or on the shop floor, one way to combat costly and deadly injuries is to implement strict operational guidelines across the organization. Operators, engineers, programmers and maintenance personnel should adhere to any and all safeguarding procedures put in place. They also need to communicate as a group when working, programming or performing routine maintenance which requires personnel to be within the “danger zone” of a particular system.
Other machines that might be more suited for the lab generally require a full environmentally sealed enclosure with interlocked doors, as mentioned above, providing a micro-climate in the manufacturing space. This scenario addresses a multitude of concerns, not just for safety, but also contamination from surrounding processes. However, having a closed environment sometimes means service and maintenance personnel might be in even closer proximity to a machine more often, providing more opportunity for accidents and injuries to occur.
Many CMMs are now built with safety features incorporated directly into the machine design. For example, when a stylus is hit accidentally, the CMM will immediately stop automatically. There are other physical safety provisions available such as a light curtain safety switch or safety pressure mat, but the best form of safety is personal and situational awareness. Following simple safety rules like not standing near or leaning against a machine in standby mode will make the workspace safer at zero cost. Not placing items inside the machine volume or on the guideways where it can become a projectile when hit with force is another way to prevent serious injury from potential flying objects.
Manufacturers now must ensure the machine operator, along with any other person who may be near one of the CMMs at any time, is thoroughly trained in emergency shut down procedures as well as machine start-up procedures after the machine is interrupted during operation. For instance, if power is interrupted during operation, will the machine turn back on automatically when power is restored? The machine turning back on and operating unexpectedly could lead to great bodily harm to anyone in the vicinity, if the proper procedures and protections are not developed, implemented and enforced. Shortcutting these or any safety procedures can lead to loss of productivity and serious injuries.
Finally, mechanical failures of course are unpredictable yet can cause serious damage and injury when they occur. One way to combat this possibility is by performing regular maintenance to your machines and ensuring they are in a safe operating condition. If the machine or the safety apparatus is not performing properly, taking it off-line for repairs may cost time and some money, but those costs are miniscule compared to injuries or death occurring because of a faulty machine. It’s best to make sure the machine is in proper operating condition and have a back-up plan for when the machine needs to be off-line for repairs. Remember, safety comes before everything else, and without safety you risk having nothing. Q