Safeguarding your processing machinery

Choosing the right safeguarding method can be difficult with so many options available. How do you know whether a simple barrier will do the trick or whether you need a more complex system involving safety mats and light curtains?

The table below provides a brief look at some of the most popular methods of safeguarding. Each method is broken down to give you a look at how they work best and their benefits and drawbacks. The intent of this article is to provide you with some basic information and steer you in the right direction to get more information about a particular device that may or may not work in your application.

Barriers and guards

• How it works

  Barriers physically restrict access to prohibit personnel from entering a guarded area. They can be moveable or permanent barriers that are installed around the perimeter of dan-gerous machinery to ensure personnel do not enter a dangerous area while the machine is in operation. Guards are smaller devices that prohibit personnel from putting fingers in hazardous areas in moving machinery.

• Best applications

  Areas that require little or no access by person-nel. For example, surrounding a totally auto-mated system that requires no maintenance.

• Worst applications

  Areas where restricted access makes the job more difficult or time consuming. This usually invites or encourages bypassing the barrier or guard, which can cause injuries.

• Benefits

  Very positive deterrent to access. No questions about functionality. Also can serve as a visual deterrent to access with colours and warning messages.

• Drawbacks

  Some type of construction will be required. By the nature of what they are intended to do they can become a nuisance if the application parameters change and access becomes necessary. Bulky.

Interlock switches

• How it works

  Interlock switches are installed on points of access barriers or perimeter guards to signal the machinery to stop when the barrier access is opened, ensuring the area is safe when the operator enters.

• Best applications

  Where personnel have full view of the guarded area from the location of the interlock device.

• Worst applications

  Large work cells where full view of the guarded area is not possible from the location of the interlock device. A second person could close the barrier, reconnect the interlock and restart the equipment.

• Benefits

  Relatively inexpensive. Easy to understand.

• Drawbacks

  Some are easily bypassed. Distribution and control of unique interlock keys can be difficult with multiple devices.

Area scanners

• How it works

  These are optical devices that send out in-frared light and look for it to be reflected back to the source. A protected area is scanned and the device learns the patterns of the reflected light of an unoccupied area. If someone then enters the guarded area, the reflected light changes, which triggers the device to send a stop command to the associated hazard.

• Best applications

  Wide open spaces with little or no obstructions. A single scanner can cover a fairly large area as long as it can 'see' the entire area with the lack of obstructions. Clean areas without a lot of dust, dirt and debris.

• Worst applications

  Tight spaces. A scanner would typically not be cost effective for a small tight space. Areas with a great deal of equipment or obstructions that would reflect the light back to the source. A scanner cannot see behind an obstruction, which would create the need for multiple scanners to see the entire area. Again, this can be ineffective from a cost standpoint. Areas with items that a person would be likely to climb up on, such as an elevated work platform above the guarded walking surface. In addition, dirty environments are not suitable for optical devices.

• Benefits

  A single unit can cover a fairly large area. Little manual labour required for installation.

• Drawbacks

  Very sophisticated and complicated device requiring a high level of expertise to install and maintain. Requires a computer to program. All the problems associated with optical devices, such as false trips due to dirty lenses, varying levels of reflectivity due to the colour or finish of the object. Inability to see behind ob-structions. Looks at a fixed plane and cannot see above or below that plane. Varying object sensitivity based on the object's distance from the sensor. Danger of installing a unit with an incorrectly learned area.

2-hand control devices

• How it works

  These are typically used as machine activation control devices and are built in such a way that both of the operator's hands must be used simultaneously to initiate the action. The positioning of the device ensures that the operator's hands are in the pre-determined area upon activation of the equipment.

• Best applications

  Confined space, repetitive cycle equipment requiring human interface on each cycle. Areas where hands are in close proximity to a confirmed hazard.

• Worst applications

  Larger equipment where additional personnel could interface with the machine. Areas where full view of the equipment or hazard is not possible from the operator station.

• Benefits

  Very positive device. Easy to understand.

• Drawbacks

  If mechanical in nature, can cause repetitive motion injuries. A timed activation with two individuals can be accomplished to defeat the purpose.

Light curtains

• How it works

  A photoelectric transmitter projects an array of synchronised, parallel infrared light beams to a receiver unit. When an object blocks one or more beams the light curtain controller sends a stop signal to the guarded machine.

• Best applications

  Light curtains can be used for point of operation guarding or as perimeter guards. They are commonly used on mechanical and hydraulic power presses, moulding presses, stamping, forming, riveting, eyelet and automated assembly machinery where the operator is in close proximity to the hazard and the hazard can cease quickly.

• Worst applications

  Light curtains do not function well in dirty environments and applications in which a great deal of debris is in the air (grinders, water jet cutters, etc). The floating debris and water will set off the light curtains, causing frequent machine downtime and operator frustration.

• Benefits

  Offer reduced operator fatigue when compared with mechanical barriers, sliding gates and pull-back restraints. Allows free access to machinery for repairs and maintenance. Simplify routine tasks like machine set-up, maintenance and repair by reducing the need for solid guards.

• Drawbacks

  All of the problems associated with optical devices, including false trips due to dirty lenses, varying levels of reflectivity due to the colour or finish of the object. Also the detection plane is narrow - once past the light curtain, the machine can be restarted.

Safety mats

• How it works

  Presence-sensing mats are used where specific area guarding is required. When someone steps on a safety mat, a signal is sent to a control box, which, in turn, sends a stop signal to the machine.

• Best applications

  Safety mats can be used for point of operation guarding or as perimeter guards in a variety of environments, including areas with high traffic and heavy amounts of fluids. Applications include robots, manufacturing work cells, food processing equipment, and automated assembly equipment, to name a few. Mats also work well in environments with excessive amounts of dirt, grease, oil and water.

• Worst applications

  Where little or no danger exists when the machine operates in close proximity to the operator. For example, punch presses requiring the operator to step back on every cycle.

• Benefits

  Offer reduced operator fatigue when compared with mechanical barriers, sliding gates and pull-back restraints. Simplify routine tasks like machine set-up, maintenance and repair by reducing the need for solid guards. Durable and reliable, Larco safety mats can be used in a variety of environments, including areas with high traffic and heavy amounts of fluids. They are more rugged than other safeguarding methods and more flexible, offering a variety of options for any application. Mats also act as a visual deterrent - unlike other devices they are not invisible to the operator and are easy to understand. Also, no adjustments are necessary - once properly installed, mats require no maintenance other than the occasional sweeping.

• Drawbacks

  Require installation labour, including drilling and cleaning. Larger mats require more handling during installation due to bulk.