Safety Check: Safety with Robotics – A Focus on Barrier and Machinery Guarding
Safety guru, Jary Winstead, covers the basics of robotics in the workplace from a safety perspective.
By Jary Winstead
Date Posted: 10/5/2018
As technology improves factory productivity, companies have to advance safety controls in the workplace. Robotics is not a sci-fi myth, robots are widely used in many manufacturing environments. This advanced automation is even starting to take root in the forest products and pallet industry. An International Federation of Robotics (IFR) report estimated a 16% increase in robotics in the United States in year 2017.
There are a number of organizations that regulate industrial equipment safety and user safety with robotics. These include: the Occupational Safety and Health Administration (OSHA), the American National Standards Institute (ANSI), and the National Safety and Health Institute (NIOSH). OSHA Standards for machinery guarding, the control of hazardous energy, and employee safety training, are adaptable throughout all industrial equipment, including robotics. In the OSHA standards there is not a lot specifically regarding robotics, but with the massive growth in robotics, that is certain to change.
According to OSHA, accident statistics have concluded that four primary types of workplace accidents involve robots:
1. Impact or Collision Accidents. Unpredicted movements, component malfunctions, or unpredicted program changes related to the robot’s arm or peripheral equipment can result in contact accidents.
2. Crushing and Trapping Accidents. A worker’s limb or other body part can be trapped between a robot’s arm and other peripheral equipment, or the individual may be physically driven into and crushed by other peripheral equipment.
3. Mechanical Part Accidents. The breakdown of the robot’s drive components, tooling or end-effector, peripheral equipment, or its power source is a mechanical accident. The release of parts, failure of gripper mechanism, or the failure of end-effector power tools are a few types of mechanical failures.
4. Other Accidents. Other accidents can result from working with robots. Equipment that supplies robot power and control represents potential electrical and pressurized fluid hazards.
This article focuses on the primary issue of machinery guarding as the most common way to ensure workplace safety when robots are deployed.
The following are OSHA Standards that relate to machine guarding. There are two Standards, including the subparts, that relate to guarding in the wood products industry: 1910.212 General requirements for all machines, and 1910.213 Woodworking machinery requirements.
Realizing that industrial space within your operation is more than just valuable, it’s difficult to guard vast spaces without losing valuable space that can be productive. At the same time, companies have to protect employees from dangerous equipment, and meet OSHA standards.
We will break down the guarding into two types of robotics:
1. Traditional Industrial Robotic Systems – These systems, once programmed, do not require workers to work in close proximity to the points of operation. Humans and robots do not occupy the same space, other than during set-up, maintenance, or repair.
2. Collaborative Robotic Systems – These robot systems interact with and share the same workspace with humans.
Traditional Robotic Systems and Collaborative Robotic Systems have the same guarding requirements, but at the same time, have unique guarding differences.
Point-of-operation barrier guards must be designed, constructed, applied, and adjusted so that individuals cannot reach through, over, under, or around the guards and reach the hazard. The closer the barrier is to the point of operation, the smaller the guard opening. Table 0-10 from OSHA 1910.217(f) provides guidance for minimum openings:
The ISO identifies four means of guarding methods for guarding machinery that can be utilized for industrial robotics.
Interlocked Barrier Guard
This is a physical barrier around a robot work envelope incorporating gates equipped with interlocks. These interlocks are designed so that all automatic operations of the robot and associated machinery will stop when any gate is opened. Restarting the operation requires closing the gate and reactivating a control switch located outside of the barrier. A typical practical barrier is an interlocked fence designed so that access through, over, under, or around the fence is not possible when the gate is closed.
Fixed Barrier Guard
A fixed barrier guard is a fence that requires tools for removal. Like the interlocked barrier guard, it prevents access through, over, under, or around the fence. It provides sufficient clearance for a worker between the guard and any robot reach, including parts held by an end-effector, to perform a specific task under controlled conditions.
Awareness Barrier Device
This is a device such as a low railing or suspended chain that defines a safety perimeter and is intended to prevent inadvertent entry into the work envelope but can be climbed over, crawled under, or stepped around. Such a device is acceptable only in situations where a hazard analysis indicates that the hazard is minimal and interlocked or fixed barrier guards are not feasible. Interlocked or fixed barrier guards provide a positive protection needed to prevent worker exposure to robotic systems hazards.
Presence Sensing Devices
The presence detectors that are most commonly used in robotics safety are pressure mats and light curtains. Floor mats (pressure sensitive mats) and light curtains (similar to arrays of photocells) can be used to detect a person stepping into a hazardous area near a robot.
The ISO/TS 15066 guidelines on safety in collaborative robotic systems lists four types of collaborative operation. These robots have integral safety systems built in that may, depending on the hazards, eliminate some guarding requirements. Collaborative systems include:
Safety-rated Monitored Stop
When it comes to the safety-rated monitored stop, the robot system stops before the human operator can access or be exposed to any hazard in the collaborative workspace. Only when there is no human operator, the robot can move as a non-collaborative robot.
In regard to the hand guiding operation, the human operator uses a hand-operated device and the robot system moves based on motion commands of the operator. It is a kind of manually controlled operation in that the operator is in direct control of the robot system’s operation. This is considered automatic operation, not manual operation.
Power and Force Limiting
The power and force limiting method assumes that the human can contact the moving robot system. Hence, we should consider the impact to human body during the risk assessment process. To prevent pain or injury, the application restricts payload and speed. As a result, the robot speed will likely be too low to be useful for high risk applications.
Speed and Separation Monitoring
In order to use the speed and separation monitoring method, external safety devices such as a safety scanner have been used to lower speed as a person approaches the collaborative workspace.
OSHA Standard 1910.212(a)(1) states that one or more methods of machine guarding must be used to protect operators and other employees from hazards, including those created by point of operation, catch point, pinch points, rotating parts, flying chips and sparks. You must keep in mind that the point of operation must include the total footprint of the robot’s operational movement, along with the material being manipulated. (See illustration #1.)
When guarding machines that perform motion tasks, guard opening must prevent a person from placing their body through the guarding. (See table 0-10.)
When the tasks performed by the machine include actions that result in flying debris; sawdust, chips, etc. the guard opening must prevent the debris from going beyond the guarding.
Hazardous Mechanical Motions and Actions
Most all industrial robotics will perform tasks that include motion, and some will perform an action. The basic types of hazardous mechanical motions and actions are:
Minimum Distance Floor to Guarding
The ANSI/RIA R15.06-1999 (R2009) states that to prevent an individual from accessing the hazard by reaching or crawling below the barrier guard, perimeter barrier guards must be designed so that the bottom of the barrier is no more than 300 mm (1 foot) above the adjacent walking surface.
Minimum Distance From Floor Surface to Top of Guarding
The ANSI/RIA R15.06-1999 (R2009) standard states that the top of the barrier must be no less than 1,500 mm (5 feet) above the adjacent walking surface.
The proper guarding is a must when it comes to using robots in the workplace. As you consider robotics and advanced automation in a lumber or pallet plant, safety must be on your agenda.
Editor’s Note: Jary Winstead is a safety consultant, author and trainer who serves a variety of industries including the forest products sector. He owns Work Safety Services LLC and can be reached at SAFEJARY@gmail.com.
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