Occupational Safety and Health Administration (OSHA) Health and Safety in Robot Environments
Industrial robots are programmable multifunctional mechanical devices designed to move material, parts, tools, or specialized devices through variable programmed motions to perform a variety of tasks. Robots are generally used to perform unsafe, hazardous, highly repetitive, and unpleasant tasks. They have many different functions such as material handling, assembly, welding, machine tool load and unload functions, painting, spraying, and so forth.
Studies indicate that many robot accidents occur during non-routine operating conditions, such as programming, maintenance, testing, setup, or adjustment. During many of these operations the worker may temporarily be within the robot's working envelope where unintended operations could result in injuries.
OSHA Instruction PUB 8-1.3 SEP 21, 1987 Office of Science and Technology Assessment
Subject: Guidelines for Robotics Safety
1. Ensure that this change is promptly forwarded to each State designee.2. Explain the technical content of this change to the State as requested.3. Inform the State designees that they are encouraged to make available Appendix A or similar guidelines to State plan personnel and appropriate employers.
E. State Consultation Projects.
1. Regional Administrators shall forward a copy of this instruction to each consultation project manager and explain the technical content where requested.2. Consultation Project Managers shall ensure that the information in Appendix A is provided to appropriate employers and ensure that copies are available for distribution to the public upon request.
The purpose of this instruction is to inform OSHA compliance officers and employers and employees about safety concerns that have arisen with the growing use of robotics systems in manufacturing. Industrial robots can be used to perform hazardous tasks but in doing so they can create new hazards. With the burgeoning use of robots in industry, it is feared that without adequate guarding and personnel training, injury rates for employees working with robots may increase.
Current guidelines for robot safety include the American National Standards Institute (ANSI) ANSI-RIA R15.06-1986, "American National Standard for Industrial Robots and Robot Systems - Safety Requirements," and the National Institute for Occupational Safety and Health (NIOSH) December, 1984 Alert "Request for Assistance in Preventing the Injury of Workers by Robots." Copies of the ANSI Standard are available from the American National Standards Institute, Inc., 1430 Broadway, New York, NY 10018. The NIOSH Alert was prepared by its Division of Safety Research, 944 Chestnut Ridge Road, Morgantown, WV 26505.
This instruction provides general introductory material describing the features of robots and robotics systems which present unusual hazards and will describe some of the more common safety systems employed to alleviate these hazards. The ANSI Standard defines consensus provisions for the construction, reconstruction, modification, installation, safeguarding, care, testing, and start-up of robots and robotics systems as well as training for robot and robotics systems operations and maintenance personnel. The NIOSH Alert contains safety recommendations that are based on its field evaluation of the first identified robot-related fatality in the United States.
Introduction
Robots are reprogrammable, multifunctional, mechanical manipulators that typically employ one or more means of power: electromechanical, hydraulic, or pneumatic. Industrial robots have been used chiefly for spray painting, spot-welding, and transfer and assembly tasks. A robot performs its tasks in a physical area known as the robot operating work envelope. This work envelope is the volume swept by all possible programmable robot movements. This includes the area where work is performed by robot tooling.
A robot can have one or more arms which are interconnected sets of links and powered joints. Arms are comprised of manipulators which support or move wrists and end-effectors. An end-effector is an accessory tool specifically designed for attachment to a robot wrist to enable the robot to perform its intended task. Examples of end-effectors include grippers, spot-weld guns, and spray paint guns. The ANSI R15.O6-1986 Standard defines an industrial robot system as that which includes industrial robots, end-effectors, and any equipment, devices and sensors required for the entire robot system to perform its tasks.
OSHA Instruction PUB 8-1.3 SEP 21, 1987 Office of Science and Technology Assessment
Most robots are set up for an operation by the teach-and-repeat technique. In this technique, a trained operator (programmer) typically uses a portable control device (commonly referred to as a teach pendant) to manually key a robot and its tasks. Program steps are of the up-down, left-right, in-out, and clockwise-counterclockwise variety. Robot speeds during these programming sessions are required to be slow. The ANSI Standard currently recommends that this slow speed should not exceed 10 in/sec (250 mm/sec).
The very nature of robotics systems operations has introduced a new type of employee into the industrial workplace, the corrective maintenance worker. This individual is normally present during all operations of a robotics system and is responsible for assuring continuing operation - adjusting speeds, correcting grips, and freeing jam-ups. The corrective maintenance worker may also be the trained programmer who guides a robot through the teach-and-repeat technique. It is necessary for this individual to be near the robot from time to time, which raises concerns about his or her safety and the safety of other workers who may also be exposed.
Recent studies in Sweden and Japan indicate that many robot accidents do not occur under normal operating conditions but rather during programming, adjustment, testing, cleaning, inspection, and repair periods. During many of these operations, the operator, programmer or corrective maintenance worker may temporarily be within the robot work envelope while power is available to moveable elements of the robot system.
This guideline describes some of the elements of good safety practices and techniques used in the section and installation of robots and robot safety systems, control devices, robot programming and employee training. A comprehensive list of safety requirements is provided in the ANSI R15.06-1986 Standard.
TYPICAL ACCIDENTS
The following are documented accidents involving robots that occurred recently in Japan, Sweden, and the United States:
- A worker attempted to remove an imperfectly formed piece from a conveyor with both hands while the operation limit switch of a material feed and removal robot remained in its active position. The worker's back was forced against the robot.- After adjusting a metal shaving machine, an operator was caught between the machine and a just-extended arm of a material feed and removal robot.
- A welding robot went functionally awry and its arm flung a worker against another machine.- A worker removed the cover of an operating assembly robot to retrieve a fallen part and caught his hand in the robot's drive train.- A worker attempted to retrieve a part needed in an ongoing assembly without shutting off an assembly robot's power supply. His hand was caught between the robot's arm and the unit being assembled.- A robot's arm functioned erratically during a programming sequence and struck the operator.- A fellow employee accidentally tripped the power switch while a maintenance worker was servicing an assembly robot. The robot's arm struck the maintenance worker's hand.- An operator performing troubleshooting on a metal plater robot maneuvered the robot's arm into a stopped position. This triggered the robot's emergency stop mode which delayed venting of a pneumatic air storage device. When the return mode was activated, the robot's arm moved suddenly and jammed the operator's thumb against a structural member.- An automatic welder robot operator made a manual adjustment without stopping the robot. He was hit in the head by one of the robot's moving parts when the next batch of weldments arrived.- A materials handling robot operator entered a robot's work envelope during operations and was pinned between the back end of the robot and a safety pole.
Safety Systems
The proper selection of an effective robotics safety system must be based on hazard analysis of the operation involving a particular robot. Among the factors to be considered in such an analysis are the task a robot is programmed to perform, the start-up and the programming procedures, environmental conditions and location of the robot, requirements for corrective tasks to sustain normal operations, human errors, and possible robot malfunctions. Sources of robot hazards include:
An effective safety system protects operators, engineers, programmers, maintenance personnel, and others who could be exposed to hazards associated with a robot's operation. A combination of methods may be used to develop an effective safety system. Redundancy and backup systems are recommended, particularly if a robot can create serious hazardous conditions.
Guarding Methods:
1. 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.
2. 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.
3. 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 inter locked 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.
4. 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. Proximity detectors operating on electrical capacitance, ultrasonics, radio frequency, laser, and television principles are currently undergoing reliability testing in research laboratories because of recognized limitations in their capability of detecting the presence of personnel. Although some of these devices are already available in the safety equipment marketplace, care must be used in their selection to insure adequate safety and reliability. At this time, such proximity detectors are not recommended for such use unless a specific analysis confirms their acceptability for the intended use.Effective presence sensing devices stop all motion of the robot if any part of a worker's body enters the protected zone. Also, they are designed to be fail-safe so that the occurrence of a failure within the device will leave it unaffected or convert it into a mode in which its failed state would not result in an accident. In some cases this means deactivation of the robot. Factors which are considered in the selection of such devices include spatial limitations of the field, environmental conditions affecting the reliability of the field, and sensing field interference due to robot operation.
5. Emergency Robot Braking
Dangerous robot movement is arrested by dynamic braking systems rather than simple power cut-off. Such brakes will counteract the effects of robot arm inertia. Cutting off all power could create hazards such as a sudden dropping of a robot's arm or flinging of a workpiece.
6. Audible and Visible Warning Systems
Audible and visible warning systems are not acceptable safeguarding methods but may be used to enhance the effectiveness of positive safeguards. The purposes of audible and visible signals need to be easily recognizable.
Control Devices: The following characteristics are essential for control devices:
Installation, Maintenance And Programming: Good installation, maintenance, and programming practices include the following:
Training: Effective accident prevention programs include training. Some points to be considered in training programs include:
(Link: https://www.osha.gov/SLTC/robotics/additionalinformation.html)
(Link: https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=1703)
National Consensus
Note: These are NOT OSHA regulations. However, they do provide guidance from their originating organizations related to worker protection.
American National Standards Institute (ANSI)
R15.06-1999, Industrial Robots and Robot Systems - Safety Requirements. Provides requirements for industrial robot manufacture, remanufacture and rebuild; robot system integration/installation; and methods of safeguarding to enhance the safety of personnel associated with the use of robots and robot systems. This second review further limits the potential requirements for any retrofit of existing systems, revises the description of control reliable circuitry, and reorganizes several clauses to enhance understanding.
TR R15.106-2006, Technical Report on Teaching Multiple Robots. Robotics Industries Association (RIA). Provides additional safety information relative to teaching (programming) multiple industrial robots in a common safeguarded space in an industrial setting. It supplements the ANSI/RIA R15.06-1999 robot safety standard.
B11.TR3-2000, Risk Assessment and Risk Reduction - A Guide to Estimate, Evaluate and Reduce Risks Associated with Machine Tools. Provides a means to identify hazards associated with a particular machine or system when used as intended, and provides a procedure to estimate, evaluate, and reduce the risks of harm to individuals associated with these hazards under the various conditions of use of that machine or system.
International Organization for Standardization (ISO)
ISO 10218-1:2006, Robots for industrial environments - Safety requirements - Part 1: Robot. Robotics Industries Association (RIA). Specifies requirements and guidelines for the inherent safe design, protective measures, and information for use of industrial robots. It describes basic hazards associated with robots, and provides requirements to eliminate or adequately reduce the risks associated with these hazards.
◦Note: ISO 10218-1:2006 does not apply to non-industrial robots although the safety principles established in ISO 10218 may be utilized for these other robots. Examples of non-industrial robot applications include, but are not limited to: undersea, military and space robots; tele-operated manipulators; prosthetics and other aids for the physically impaired; micro-robots (displacement <1 mm); surgery or healthcare; and service or consumer products.
Canadian Standards Association (CSA)
Z434-03, Industrial Robots and Robot Systems. Applies to the manufacture, remanufacture, rebuild, installation, safeguarding, maintenance and repair, testing and start-up, and personnel training requirements for industrial robots and robot systems.
American Welding Society (AWS)
D16.1M/D16.1, Specification For Robotic Arc Welding Safety. Identifies hazards involved in maintaining, operating, integrating, and setting up arc welding robot systems.