To stop users from disabling critical machine sequences, talk stirs occasionally to return to the use of proprietary control boards and code for safety reasons. But does a machine builder's role in designing a system that can't be defeated go beyond a defensible risk assessment and the accompanying due diligence?
"When using any software in a safety application, the machine builder must ensure the highest level of due diligence during the design and validation process," explains Juergen Bukowski, safety program manager, Sick (www.sickusa.com). "Consider the average PLC programmer or user whose job is to get the application running, but doesn't know or understand how to stop it safely. This is a recipe for disaster, since they are not typically involved in the safety concept or trained in failure-mode analysis. Keep safety as an external part of your automation project or process."
In the eyes of OSHA, the end user/owner of the machine is directly responsible for safety of the employees, explains Mike Garrick, product marketing lead specialist for interface, Phoenix Contact (www.phoenixcontact.com). "However, everyone also knows that the machine builder is in the most obvious path of civil litigation of an accident occurring during the use of the machine," he says. "The machine builder absolutely needs to make every effort to make a machine as safe as possible. A machine builder's reputation is important for success, and accidents will only subtract from how the company is perceived."
As part of the machine design, engineers need to help ensure safety while maximizing productivity during the initial setup and installation, operation, maintenance and decommissioning phases of the machine, says Tim Roback, marketing manager, safety systems, control and visualization, Rockwell Automation (www.rockwellautomation.com). "In addition, machine designers also must consider the domain of foreseeable misuse," he says. "This misuse can extend into programming changes to the control or safety system."
Multifunctional gate box MGB is designed to combine all necessary requirements to protect a safety door in accordance with EN ISO 13849 and EN 1088. The core of the modular system is the evaluation module, available with and without guard locking. Combined with a handle module and an optional escape release, MGB is designed to protect almost every safety door.
Diagnostics Add-On Instruction for CompactLogix and ControlLogix controllers, available as a free download, is designed to enable PLC programmers to retrieve detailed diagnostic data from an AS-Interface safety monitor and to be compatible with competitive AS-Interface Safety at Work safety monitors.
NE0A-SCPU01 safety network controller provides 12 safety inputs, two test outputs and six safety outputs, and can be used as a stand-alone controller, safety slave or DeviceNet standard slave. It has preconfigured and TÜV-certified program templates to select based on an application's safety requirements, potentially eliminating programming needs. Users can create safety circuits and save them as templates and reuse them on multiple NE0A units.
Omron Scientific Technologies
Interface and Intrinsic Safety Quick Reference Guide of the company's intrinsically safe products includes switching amplifiers, analog I/O, solenoid drivers, rotational speed monitors and relay and power supplies. The guide allows users to select the correct amplifier for a specific application and showcases unique, out-of-the-panel solutions for intrinsic safety.
E-Box for RAFIX 22 FS-type actuators has a yellow housing cap for e-stop buttons or a gray cap for push buttons or selector switches. E-Box is suited for installation on 40 mm profile rails. Contact modules are available with gold contacts for 35 V and 100 mA or silver contacts for 250 V and 4 A.
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HS5D compact interlock safety switches available with three contacts monitor if the head is separated or improperly mounted on the body. The switches are available with metal or plastic heads; the metal head can be rotated eight ways based on actuator entry, providing mounting flexibility.
L43S and L45S Compact GuardLogix programmable automation controllers (PACs) add diagnostics and information capabilities and single-programming environment previously available only in ControlLogix. GuardLogix PACs can control eight axes of integrated motion over SERCOS. Used in combination with Kinetix 6200 servo drives, users gain advanced safe-speed and safe-direction safety options.