Robot Hazards
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Robot Hazards
Introduction: the aim of this assignment is to gain general awareness and an understanding of the legal requirements and responsibilities that are involved in the safe working practices associated with robotic assisted manufacture. This is to be achieved by the identification of associated hazards with robotic applications and provide an understanding of how these hazards are overcome.
Typical sources of hazards associated with robotic operations within the working environment include.
Crushing
Shearing
Striking
Entrapment / entanglement
Process hazards such as toxic fumes, welding flash, lasers, dust, coolant, high-pressure water jet, unguarded abrasive wheel etc.
Fire – if the robot is functions by use of hydraulics
As a matter of good system design all moving parts of the robot system should by design or enclosure eliminate / minimise all possibilities of the above from happening
The source for theses types of hazards can be caused by
Unknown / unintentional or un-covenanted movements – this could be in the form of unpredictable movements whilst the equipment is being maintained or at the reinstatement of power. Other causes may be due to the corruption of software, or damage to the any of the peripherals or programmable electronics.
End effecter malfunction, which may result in a component ejection hazard, which can be due to a malfunction of the control system, or programming error.
Both of the above may occur as a result of a pneumatic or hydraulic equipment dump fault, as either may have a reservoir and could be subjected to sudden movements of one or more actuators when a jam-up is freed.
Hazards may arise from problems when interfacing with other machinery and equipment, especially if the associated machines and equipment are out of programmed sequence with that of the interfacing electronics.
The numerous safety devices that are associated with robotic operations are implemented to only allow access to the robot when the machines movements have fully stopped and or prevent access to the machine during normal operation thus the possibility of the hazards mention above will be reduced or even eliminated. The devices used to accomplish this include:
Safety Mats
Pressure-sensitive mats and floors are devices with a sensitive upper surface so that the pressure applied by a person standing on them will cause dangerous motion to stop. Care should be taken to ensure that access couldnt be gained without actuating the mat.
Interlocks
Interlock are used to allow Access to the enclosure when the robot and associated equipment has fully and prevents it from resuming until the safeguards reinstated
Examples of interlocking devices include:
Guard-operated interlocking devices designed for use in safety systems
Key-interlocking devices (trapped key-interlocking) is a common method. In the case of hydraulic and pneumatic equipment, the lock would need to be on a valve actuator. The key cannot be removed from the robot controller (or valve actuator) lock to open the gate lock until a safe condition is established
Solenoid locks, this is an electromechanical device activated by an electrical signal. When the signal is received the locking bolt is withdrawn, allowing the access gate to be opened or a second key to be released which in turn releases the gate.
Light Beams and Light curtains
These are the most commonly used sensing devices. They operate by detecting an obstruction in the path taken by a beam or beams of light (a curtain of light).
The light may be visible or invisible (infra-red), and may be continuous or modulated (a scanning system).
Light curtains have three basic uses in safeguarding systems:
* as a trip device where the light curtains are usually arranged in a vertical format
* as a presence-sensing device where the light curtain is usually arranged in a horizontal format
* a combination or zoning system where two or more may be used as sensors and/or trip devices to provide a more complete or selective protection against access to the moving robot or associated dangerous machinery
The biggest drawback with a light curtain though is that it cannot protect against an ejection hazard, of tools or work pieces being handled by the robot.
Laser scanning devices
These are single devices which function by the use of a scanning laser beam to view and map an area.
This works by use of a two-dimensional sensing zone, this zone is programmable thus enabling it to recognise any stationary equipment within the scanning zone.
Guards / Physical Barriers
The standard barrier used to prevent access to a robot consists of a perimeter fence that is made from 2 m-high rigid panels securely fastened to the floor or to some convenient structure and positioned so that it is not possible to reach any dangerous parts of machinery.
The possibility of component ejection should also be considered when designing this type of barrier. Fixed transparent barriers may be adequate. For most purposes, a hollow section steel framework in-filled with mesh is satisfactory.
Where regular access is required, the fencing may be provided with sliding or hinged interlocked access gates; and/or an opening protected by a trip device.
Brakes or hydraulic/pneumatic stop valves
Should be incorporated to prevent the robot from moving or cause the gripper to release the load when power is removed. Such as that in the event of an emergency stop.
Brakes should be provided where there is the danger of gravity fall of a robot arm due to removal of power. It should be capable of supporting the weight of the robot arm and the weight of the largest tool or work piece likely to be used. Brakes may also be used as a back-up system to other forms of safeguarding,