Robot Safety

Venturing within reach of a robot while it is in operation is never a good idea, but at times it is required when servicing or dealing with operational disruptions. Robot Operators may also work in close proximity to a robot at times, for example while loading or unloading feed devices and work pieces. With the speed and power of today's industrial robots it is necessary to safeguard from all possible hazards.

The measures taken to safeguard a robot will entirely depend on the circumstances of its operation and surrounding environment. However any safeguarding put in place will be done so with the intention of keeping people at a safe distance from the robot while it is operating and ensuring the robot and equipment is in a safe state in the instances where access is required. Where possible it is also desirable that the safeguarding permit teaching, programming and configuration of the robot which is normally done with close operator interaction.

The most common safeguards are described below:-

• Perimeter Fencing
  Made from rigid panels which can be fixed to the floor or other suitable points yet must remain removable via a tool only. Where possible the robot and/or work piece must be viewable, however the material used must be suited for the activity undertaken within the enclosure. For example a mesh would restrict access to purely moving parts but would not stop projectile hazards such as the flash from a welding torch. If regular access is required, it must be allowed via a gated entrance with the appropriate safety mechanisms.
• Interlocking Devices
  Such as guard operated interlocking devices, key interlocking devices (transfer of key from control to access gate) or solenoid locks.
• Light Curtains
  If an obstruction is detected within the path of the beam an output is triggered. This method provides instant access to the workspace and multiple instances can provide different safety zones. However they cannot shield against projectile hazards.
• Laser Scanning Devices
  These devices use a single laser beam to map an area and detect any changes which would signify a potential hazard and trigger an output. Normally placed below the working level of the robot.
• Capacitance Device
  Consist of a capacitive loop connected to a high frequency oscillator. Disturbance of the electrical field triggers an output.
• Pressure Sensitive Mats
  Triggers an output if pressure is applied to the surface. Length of stride, speed of approach and system response time must be considered in placement.
• Two Hand Control Devices
  Two hands are required to use this hold-to-run control ensuring both hands are clear of moving parts during operation. The robot should stop when either button is released and modes cannot be changed while the buttons are held down.
• Pressure Sensitive Edges
  Flexible edging strips which can be fixed to the edge of a moving part such as a machine table or powered door where there is a risk of a crushing or shearing hazard. If the moving part comes in contact with an object the flexible sensitive edge is depressed and triggers an output.
• Trip Devices
  Trip wires can be used to trigger outputs.
• Positive Stops
  Limits the movement of a robot to exclude the area required by an operator.
• Brakes
  Used to support the weight of the arm and object in the event of a power failure.
• Emergency Stop Buttons
  Must be located so that they are easily within reach at all times.
• Enabling Devices
  Used in conjunction with other devices to ensure that operation can not begin unless the device is actuated.

It must be ensured that the operational mode of the robot cannot be changed from teach to automatic while someone is present within the working range. This can be achieved by using a mechanism to lock the mode such as a password or key.

Any access gates in the guarding that must remain open to ensure a safe environment should contain a physical means of securing the gate open.

In situations where close proximity to the robot is required while it is moving, speed must be restricted to no more than 0.25m per second at any point of the robot to limit potential impact force and avoid trapping. Again, this should not be controlled by anyone other than the operator in close proximity who must have the means of controlling the robots movement via a hold-to-teach button and an emergency stop button.

Equipment should be placed no closer than 500mm to the robot at full reach (excluding work pieces etc) to avoid severe injury should an operator be pinned against it by the robot.

The software written to control the robot should be protected form unauthorized editing and corruption.

All personnel, be it operators or cleaners, should be trained on procedures around the robot suitable to their role. It is worth considering that should an accident occur that endangers another person's life, even a passer by may attempt to access the workspace. Therefore it is important to make sure they are aware of how to make the environment safe before entering. Highly visible notices, visible markings and clear display of procedures should be made use of along side thorough training.

With any safeguarding methods implemented, constant vigilance is required to avoid 'jumpers' which are methods used by operators or just as likely, maintenance personnel and industry professionals from bypassing the safeguards. Jumpers are more likely where unnecessary amounts of safeguarding have been put in place which begins to infringe on production and makes the role of users unnecessarily complex or frustrating. They are also common in situations where there are regular occurrences of stops as a result of safeguarding devices. Industry experts and Accident Investigators say that jumpers are the cause of nearly every accident within robot cells. The key is to making a cell in which operators, maintenance staff and service engineers work alongside safety measures and not against them.