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| Date:
05/15/97 |
Bulletin Title:
Safety - Technical |
Responsible Activity:
Occupational Health and Safety |
Bulletin No.:
131 |
| Subject:
ROBOT SAFETY STANDARD |
Supercedes:
Corporate Robot Safety Guidelines Dated 01/19/94 | ||
This standard is designed to ensure the safety of personnel when operating, maintaining and servicing robots. It should be understood this standard may be revised as a result of technical developments, practical experience or new applications. Under such circumstances, a deviation to the standard shall be approved in writing by the appropriate Division Safety Engineer and approval forwarded to the Corporate Safety Office.
The standard described in this bulletin applies to robot installations without regard to robot manufacturers or processed task.
The following is a list of common terms used in discussions involving robots: (Some of these definitions are excerpts from other published lists of definitions.)
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Robotic Industries Association definition of Industrial Robot "Reprogrammable, multifunctional manipulator designed to move materials, parts, tools or specialized devices through variable programmed motions for the performance of a variety of tasks." |
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Barrier A physical means to prevent personnel from reaching the restricted envelope and associated hazards. |
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Non-Mechanical Limiting Devices - Control devices such as, but not limited to, limit switches, relays, pull plugs or blocking valves may be utilized provided the device and associated controls are capable of stopping the robot motion under rated load and speed conditions within the restricted envelope or space. Non-mechanical limiting devices shall be designed to achieve control reliability, as defined in ANSI B11.19 (see following). Robots must still be outfitted with mechanical stops. |
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Control Reliability - Safety devices and related control systems shall be designed and constructed so that a single failure or fault within the system does not prevent the normal stopping action from being applied, or does not create an unintended cycle, but does prevent initiation of a successive cycle until the failure is corrected. This requirement shall apply to all newly manufactured robots and robot systems within eighteen months of the issue date of this standard. The requirements of this standard shall apply to existing robots when remanufactured or rebuilt. Safeguarding methods used to protect workers in existing robot/worker shared workstation applications shall be retrofitted with control reliable circuitry and components (see Attachment 1, #4). |
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Emergency Stop An electrical circuit that overrides all other robot controls, removes drive power from the robot, and causes all moving parts to stop. |
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Enabling Device A manually operated device, which when continuously activated, permits robot motion. Releasing the device shall stop robot motion. |
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Mechanical Hard Stops Adjustable limiting devices capable of stopping the motion of the robot under rated load, maximum speed conditions and at maximum extension. Hard stops shall be adjusted to minimize robot movement to a space slightly larger than that required to perform the program task(s). |
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Motion Hold A state of operation of an industrial robot in which power has been removed from the prime movers of the robotics mechanical arm and brakes have been engaged on those axes so equipped. Removal of power to the prime movers shall be accomplished through a mechanical means and must be initiated at the main control location after safety circuits have been reestablished. |
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Multifunctional The capability to perform a variety of work duties in a single operating location. |
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Reprogrammable The ability to change performance duties without physically modifying the inherent design of the control physical structure and/or its power source. |
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Retractable Hard Stop A cycling hard stop which meets all of the requirements of a mechanical hardstop. Retractable hard stops and associated control circuits must be designed and constructed to be control reliable (see previous terminology). Retractable hard stops will be hardwired and not depend on computer hardware or software. |
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Retractable Pins A physical pin which restricts the base rotation of a robot to a fixed position. The pin is capable of holding the robot and preventing base rotation if motor power is applied. The stop position is controlled by the robot program and monitored in the safety circuit. |
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Robot Restricted Space - That portion of the maximum space to which a robot is restricted by mechanical stops. Robot movement may be further limited by retractable hard stops or non-mechanical limiting devices. The boundaries of the restricted space are defined by the mechanical stops and will not be exceeded in the event of any foreseeable failure of the robot or its controls. |
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Single Point of Control The ability to initiate robot motion from only one control source that cannot be overridden from any other source. |
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Variety of Tasks Inherently capable of performing assignments that span more than one special area of application types such as material handling, machine loading, welding (arc & resistance), coating, machining, etc., with little or no basic robot design change. |
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Variable Programmed Motions The capability to vary stopping point locations and/or path trajectories of the tool center point in space by the act of programming the work sequence of the manipulator. |
Employees whose assigned task involves working with robots shall have sufficient instruction prior to work assignment to permit them to work with or around robots without endangering themselves, others or equipment. Records of all personnel completing robot training shall be maintained.
4.1 Training can be provided by the robot manufacturer (recommended), or by qualified Company personnel approved by the plant safety engineer.
5.1.1 The robot restricted space and the work station shall be guarded. Hinged gate sections shall be interlocked into the electrical circuit which will, when disconnected, prevent or stop the robot and related equipment from operating in the normal run or automatic mode. Disconnecting an interlock shall not be a substitute for power lockout.
5.1.2 Even though the robot is programmed to operate in a smaller area (robot operating space), the guarded area shall incorporate dimensions and distances to protect the restricted space of the robot and allow adequate clearances to teach the robot and maintain equipment.
5.1.3 The robot control console shall be located outside the safeguarded space. It shall be positioned to allow the employee to operate the console without being exposed to the robot and with the robot in view.
5.1.4 Guarding shall be designed to prevent access to the robot restricted space during automatic operation.
5.1.5 Where it is not possible to enclose the robot working area with barrier guarding, control reliable devices shall be utilized which prevent the robot from moving into an operator's work area and/or the operator from moving into the robot's restricted space (i.e., presence sensing devices, pressure sensitive mats, retractable hard stops, etc.). Procedures for authorized and controlled entry shall be posted in the area. See attachment #1 for Safety Requirements for Robot/Worker shared work station.
5.1.6 Where routine maintenance (not programming) is to be performed on the robot, while the machinery/equipment normally served by the robot is operational, these machines shall be guarded from inadvertent entry. They shall be locked out prior to any physical exposure to machine action.
5.2 All entry points into robot cells shall be posted with a sign bearing the legend "Restricted Authorized Personnel Only."
6.1 The guarding method (barrier, presence sensing etc.) shall be approved by the plant safety engineer.
6.2 Applicable barrier guards enclosing a robot envelope and work station shall be designed, fabricated and installed in accordance with Ford Manufacturing Standard KZ3X1. Barriers guards shall prevent personnel from going over, under, around or through. Guard openings shall comply with Table O-10 of OSHA 1910.217.
6.3 All entry points through barrier guards (i.e., hinged gates) shall be appropriately interlocked with approved safety devices. (See Ford Manufacturing Standard EP1 for Guidelines.)
6.4 Barrier guard height shall be determined by the potential hazards and approved by the plant safety engineer, but in no case shall guarding be less than 60 inches from the floor.
6.5 Presence Sensing Devices should be interlocked to interrupt the run circuit and cause a motion hold condition when the sensing field is intruded. Wiring of the presence sensing device shall conform to Ford Manufacturing Standard EL4, 4.1.5.
7.1.1 It shall not be possible to restart the robot until the emergency stop device has been manually reset. Resetting the emergency stop device shall not cause the robot and/or associated equipment to operate. Restarting shall be possible only at the start control panel.
7.1.2a All operator control stations capable of initiating robot motion shall have Emergency Stop devices. Any Emergency Stop actuation shall cause immediate interruption of motion of the robot and related equipment for any further sequence or actuation steps. Restoration of the work station to normal operation will require a restart to resume automatic operation.
7.1.2b Unless provisions are included in the robot and tooling design that maintains the manipulator pose in a mechanically fixed state and releasable objects held in steadfast containment by the endeffector when drive power ceases and stored energy is dissipated, the use of Emergency Stop devices in operating and programming modes should be approached with caution. Where these design conditions do not prevail, an alternative such as motion hold control button for use in an emergency situation shall be considered acceptable. In this instance, restart of the operation must comply with the same conditions of "noautorestart" after emergency condition causes are cleared.
7.1.3 Emergency Stop pushbutton(s) shall be red in color and Motion Hold pushbutton(s) orange. Either are to be the palm or mushroom type head.
7.1.4 All control devices shall be clearly marked and labelled as to their purpose.
7.1.5 Loss of Power - End effectors shall be designed and constructed so that a loss or change of electrical, hydraulic, pneumatic or vacuum power shall not result in a hazard. If this is not feasible, then other methods of safeguarding shall be provided to protect against hazards.
7.2 Closing a safety interlock shall not cause the robot and/or associated equipment to operate. Restarting the equipment shall only be possible at the station or main control panel after ensuring personnel are clear of equipment, out of the envelope area and that all related safety devices are operating properly.
7.3 All electrical safety devices shall be hardwired into the machine operation control circuit and function through electromechanical contacts and shall not be PLC logic dependent only. Refer to Ford Manufacturing Standard EL3X.
7.4 All safety function circuits, including emergency stops, enabling devices, and axis drive disabling circuits, shall be designed, constructed and applied such that any single component failure shall not prevent the stopping action of the robot and prevent the initiation of a subsequent cycle.
8.1 The teacher shall have single point of control.
8.2 If programming cannot be accomplished without exposure to hazards of associated machines and/or equipment, appropriate safeguarding shall be provided to prevent exposure of the teacher to a hazardous environment.
8.3 Detachable teach pendants, keyboards, programming tapes, etc., shall be properly secured to prevent alteration of programs by unauthorized personnel.
8.4 When teach mode is selected, the velocity of the robot shall be reduced to a slow speed so that any part of the robot shall not exceed 250 millimeters/second (10 inches/second). It shall not be possible to run the robot at full program speed using the pendant control.
8.5 Only one person shall be inside the guard enclosure when a robot is in a teach mode and being programmed. Any deviation must be approved by the appropriate division safety engineer.
9.1 All teach pendants shall be equipped with an enabling device.
9.2 The teach pendant shall be equipped with controls which require constant pressure for robot movement when used in teach/programming mode.
9.3 Pendants shall be designed with single point of control protection, so that when the robot is under pendant control, initiation of robot motion shall be prevented from any other source.
9.4 A pendant shall include a robot emergency stop button.
10.1 Energy Control/Power Lockout procedures shall be provided and enforced for all robot installations as detailed in Human Resources Bulletin SafetyTechnical Bulletin No. 100, (latest edition).
11.1 If safeguarding controls, devices and/or procedures are in place to prevent inadvertent access to the work station automation and other robots in a multiple robot system, then provisions to enter the safeguarded area by trained and authorized personnel for tip dressing or similar routine tool maintenance are permitted. A safe Procedure must be approved by the plant safety engineer and posted in the area.
The following requirements are mandatory when a robot and employee share a work station.
1. The system must be provided with operator control(s) interfaced to the robot controls and an approved infrared presence sensing device. Initiation of the operator control(s) shall be required for each cycle and must reset the presence sensing device before initiating the robot cycle into the shared work station.
2. An approved presence sensing device must be mounted on the operator side of the work station. This device must be interfaced with the operator control(s) and the robot circuitry so that any intrusion of the sensing field, after the robot cycle has been initiated with the operator control(s), will result in an emergency stop condition of the robot and related equipment.
3. The work station must be designed so the position of the robot at maximum extension does not extend beyond the presence sensing device. (The employee is ahead of the presence sensing device.) This can be accomplished by providing proper distance between the robot and the employee or by providing hardstop devices that will restrict the robot's movement to a position behind the presence sensing device.
4. Where a presence sensing device is being used to restrict the robot space and also restrict the operator from entering the robot's restricted space, the presence sensing device shall be retrofitted to be control reliable on existing robot/employee shared work stations.
5. The process operation sequence must be controlled so that the robot and employee are not working in the shared work area at the same time.
Printed Copies are for
Personal Reference Only.
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© Copyright 1995-2003 Ford
Occupational Health & Safety |
