Page 46 - MetalForming-Feb-2018-issue

Press Safety
Starts with Proper Guarding
A—Stampers sometimes mount the light curtain too high, as shown here. Also, this application shows the bottom
8 to 10 in. of the light curtain blanked to allow scrap and parts to exit through the rear, which has left the backside of the press unguarded.
...that protects personnel without compromising productivity. Here’s a deep-dive into the fundamentals of light- curtain technology, along with tips for its proper application in the pressroom.
BY TODD WENZEL
When applied properly, light curtains provide met- alformers with an effective, easy-to-use press-safe- guarding scheme that will not negatively affect productivity. Unfortunately, we often see light curtains mis- applied, leading to operators working with a false sense of security as hazards remain unguarded.
Light curtains comprise an array of transmitters that emit infrared light toward a mating receiver that features an array of sensors tuned to receive the transmitted light. Control- reliable solid-state controls in the lights cause the transmitters to produce brief pulses of infrared light in a sequence, cycling from one end to the other. Those same controls monitor the sensors in the receiver and can react if an expected light burst is not received, indicating that an object has passed between the transmitter and receiver.
To ensure proper application of light curtains as pres- ence-sensing guards in a press cell, stampers should first understand these fundamental concepts:
• Control reliability
• Safety distance
• Minimum object sensitivity, and
Todd Wenzel is president of TCR, Inc., Wisconsin Rapids, WI: 800/676-2240; www.stampingsystems.com.
• The use of complementary physical guards and addi- tional light curtains to prevent operators from reaching around, under or over the sensing field.
Control Reliability
In layman’s terms, a control-reliable control includes cir- cuits comprised of redundant, checked components. No one component is used in any decision that impacts safety; two must act in agreement. Also, the control cycles and monitors all control elements to ensure that they are oper- ational. If two of the checked components disagree on a decision, the system opens the safety relay to stop the press.
Therefore, light curtains must employ control-reliable control circuitry that monitors the light’s logic elements. (All modern light curtains that we are aware of meet this standard.) Further, for applications requiring hands-in-die production, OSHA requires that the press also employ a control-reliable control; the ANSI standard also requires, in all cases, control-reliable controls on presses.
44 MetalForming/February 2018
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