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Revised rules for robot safety

Sept. 1, 1999
The newly revised robot-safety standard now requires minimum safety criteria, and companies may have to retrofit some

The newly revised robot-safety standard now requires minimum safety criteria, and companies may have to retrofit some

Robotic cells like the one seen here for arc welding must include devices designed to protect operators and passers-by from the hazards of automated manufacturing. Manufacturers of the equipment, as well as integrators and users, select among a variety of machine-safeguarding devices, including barrier guards, which must be free of sharp edges and securely attached. On the cell shown, a Versa 1 from Genesis Systems Group, an access door to the cell must be closed in order for the worktable to index.

The Robotic Industries Association (RIA) has released its new robot-safety standard, ANSI/RIA R15.06-1999. This newly approved American National Standard replaces the 1992 edition of the robot-safety standard and provides significantly more information and guidance in properly safeguarding personnel from injury in robotic-production applications. Sponsored by the RIA, the North American trade association for the robotic industry, the standard has continued to expand safety awareness throughout the robotics industry.

Publication of the new standard marks the completion of an extensive four-year development period. It included the active participation of more than 50 people on the drafting committee. The committee goals were to:

  • Make the standard more userfriendly and easier to understand
  • Improve the safety of personnel and the safeguarding of robots and robotic systems
  • Address real-world issues regarding robot applications, including protecting personnel from the hazards presented by automated manufacturing while still meeting the production requirements of modern industry.

All you need to know R15.06-1999, titled American National Standard for Industrial Robots and Robot Systems— Safety Requirements, provides valuable information to both the experienced integrator and the novice user. The information applies to multiple applications—welding, cutting, machine tending, assembly, material handling, and others. It serves as a source for "one-stop shopping" for appropriate safeguarding equipment and techniques for robotic applications.

For anyone familiar with the old standard, the difference in the new standard is striking. New sections address safe-guarding-device requirements and installation. The format and organization has been changed to make it easier to read and understand.

The standard now offers a choice in safeguarding strategies—a prescribed method for risk assessment. The tasks of teaching a robot and of verifying the task program have been clearly separated, with specific safeguard requirements delineated for each task. Also, to improve understanding, the term "space," referring to the robot's workspace, has replaced the engineering term "envelope."

Performance requirements
Safeguarding devices are now discussed in considerable detail. One complete section calls out performance requirements for specific types of devices. These requirements must be met by the device manufacturer for the device to qualify for use in a robotic-safeguarding application. Another section describes in detail the requirements for installing the devices and the possible uses for the devices.

Those responsible for the design and maintenance of robotic work-cells need to become familiar with the new provisions of this standard. Unlike previous editions, the standard now requires minimum safety criteria, and retrofit of some existing systems may be necessary.

In addition to being in compliance with the version of the standard that was in effect when a workcell was installed, it must also be "guarded such that intrusion into the restricted space will interrupt the automatic cycle of the robot task program." This provision establishes a baseline for what minimally acceptable safeguarding is necessary in a robot application. An NFPA 79-compliant emergency stop is also required, as are additional provisions for pendants used inside the workcell and precautions to be used in applications where high-speed Attended Program Verification (APV) is allowed.

Selection criteria, circuitry integration, and installation requirements are detailed for a number of safeguarding devices, both mechanical and presence sensing. Included are most common safeguarding devices, barriers, light curtains, and safety mats, as well as some less common safeguarding devices, two-hand controls, area scanners, light beams and RF capacitance systems. Installation issues such as dynamic limiting, bypassing, muting, and presence-sensing device initiation are addressed. Determining safety distance is also discussed and this section includes updated tables. Drawings in an annex help users understand safeguard-installation issues.

Specific safeguarding requirements
Barrier guards need to be free of sharp edges and be able to be securely attached.

Mechanical devices need a physical link between the energy source of a hazard and the locking mechanism to allow removal of the key (for key-interlocked devices) only when the hazard has been controlled. They must also provide a mechanical lock for the guard at the point of access that can only be unlocked by the key.

Electrical devices, such as safety switches, shall provide a method to unlock the device in the event of power failure and provide a method to monitor the state of the locking mechanism.

Safety light curtains must be marked with their maximum response time, maximum angle of divergence, minimum object sensitivity, and protected height. They need to visibly indicate a fixed blanked area; if not, the user shall verify that blanking is being used, including the number, size, and location of the blanked beams.

RF/capacitance devices need to have a sensitivity adjustment to allow for authorized adjustment of the field and must not be adversely affected by external fields such as those created by welding.

Safety mats must have a minimum object sensitivity that detects a 30-kg (66-lb) weight on an 80-mm (3.125-in.) diameter circular disk placed anywhere on the mat sensing surface. Mats need to be securely mounted to prevent inadvertent movement or removal and installed so as to minimize tripping hazards, typically achieved by use of ramped edging. Maximum response time should be less than 100 msec, measured over the system operating-temperature range.

New installations closely scrutinized
Plans for new robot-workcell installations need to include a number of new or better-specified provisions. The standard now requires minimum safety-circuit performance, intended to increase in performance reliability as the severity of potential injury from associated hazards increases. Also new is the requirement for two distinct stopping circuits, one dedicated to emergency stop, the other used for signaled stops from safeguarding devices or operator interventions.

The section on Risk Assessment now includes detailed information and criteria for performing a satisfactory risk assessment. A suggested methodology with detailed mechanics is offered as an annex to the standard. For those not wanting to perform a risk assessment, and in response to comments from the 1992 standard, an option for a prescribed method of safeguarding has been added. This section walks the user through a sequence of safeguarding steps that will result in a properly safeguarded installation.

Finally, the new robot safety standard has detailed specific safeguarding steps to protect the teacher when working in the safeguarded space of the robotic workcell.

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