Expanded use of automation and the changing makeup of the industrial workforce are resulting in new workplace safety challenges. OSHA holds that employers are responsible for providing a safe and healthful workplace. Regulations, standards, and common sense, then, dictate machine safeguarding methods and applications.
Switches, relays, and controllers
Machines should not be operated without physical guards in place. Electrical interlocking to ensure that the guard is closed or in position is usually accomplished using safety limit switches, such as Banner Engineering’s SI Series Safety Limit Switches.
“The difference between a standard limit switch and a safety limit switch is the design of ‘positive opening’ normally closed (safety) contacts that are not dependent on springs,” says Mike Carlson, Banner’s safety products manager. “This forced opening of the normally closed contact reduces the possible unsafe failures that could result in loss of the switching action.” He adds: “Using redundant, individually mounted and monitored safety limit switches is recommended for applications that have a high risk of injury.”
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The new Sirius 3SK2 safety relays from Siemens offer as many as six safety functions that are configured with drag-and-drop Safety ES software. Complex safety applications, such as noncontact-area access monitoring through muting, can be easily implemented with the 3SK2 system. Device connectors allow for rapid expansion – for instance, via additional failsafe outputs or 3RM1 motor starters – without the need for additional control wiring.
“The 3SK2 system represents a solution for those applications where a simple safety relay is not quite enough, but a safety PLC is overkill,” says Glenn Symonds, product manager at Siemens Industry. “3SK2 offers simple configuration of safety functions through free assignment of inputs and outputs, selectable time delay, and automated user documentation, all through the Safety ES software.”
Variable-frequency drives with integrated, over-the-network safety reduce the need for contractors and relays. The new Allen-Bradley PowerFlex 527 AC drive from Rockwell Automation offers this capability. Embedded hardware or network-safe torque-off options are available to help protect personnel and assets.
“The PowerFlex 527 drive uses a standard Ethernet/IP infrastructure, which enables networked safety,” says Jimmy Koh, business manager for components drives at Rockwell Automation. “This functionality helps reduce the hardware, wiring, and labor costs associated with implementing a SIL 3/PLe safety solution. It also reduces panel space and allows access to more diagnostic data on machine safety faults and causes.”
Sensors and scanners
Explosion-proof light curtains are beneficial where moving applications such as robots or presses operate in an explosive environment due to paint fumes, dust, chemicals, or pharmaceuticals. The deTec4 Core Explosion Proof safety light curtain from SICK provides protection from moving and explosion hazards and is UL-listed for use in hazardous locations.
“The deTec4 Core provides hand protection to prevent personnel access to the hazardous movement, while the explosion-proof enclosure minimizes the possibility of the ignitable elements combusting by containing the electrical hazards of the safety light curtain,” says Aaron Woytcke, SICK’s national product specialist for industrial safety systems.
Safety laser scanners, which establish zones of protection, are used for collision avoidance, presence detection, and intrusion detection applications. Battery-powered systems such as automated guided vehicles (AGV) can benefit from the small size, light weight, and lower power consumption of the OS32C safety laser scanner from Omron Automation and Safety.
“For complex AGV applications, up to 70 zone combinations are available, each with one safety zone and two warning zones,” says Mike Frey, product manager at Omron. “The two warning zones can be configured to support an audible or visual warning and also the speed of the AGV when an object is detected in the warning zone, allowing the AGV to reduce speed.”
Physical barriers
In warehouses and distribution centers, machine operators need protection from automated processes and equipment such as stretch wrappers and packaging machines. The Defender Cell safety barrier system from Rite-Hite effectively separates workers from these potentially dangerous automated processes.
“Eight-gauge welded steel wire restricts workers from entering work spaces where machinery might be moving,” says Eric Esson, global sales manager of Rite-Hite Machine Guarding. “On the fourth side of the cell, a high-speed, high-cycle automated door – the Defender – protects machine operators from entering the work cell during operation and provides safe and easy access to the work space when the machine is powered down.”