Page 48 - MetalForming-Feb-2018-issue

Press Safety
D and E—Physical barriers, positioned along with light curtains using a manual reset, create a guarded zone that protects the rear of the press. In this case the light curtain is 5 ft. from the hazard. An entire scrap bin can fit inside the zone, easily accommodating scrap without compromising safety. Workers approaching the rear of the bolster must pass through the light curtains, which will enter a fault state and remain faulted until the personnel exit the area and reset the lights with a key.
Barrier guard
The maximum actual measured time value the brake monitor will accept without faulting is a critical portion of the stop time formula. That brake-monitor limit determines the proper placement of the light curtain, not the average stop time measured when installing the light curtains. Take care to place the light curtains at or beyond the distance that the formula deems as safe when the stop time reaches the maximum brake-monitor limit. This protects operators as braking time gradually increases.
Depth Penetration Factor
This factor relates to the light curtain’s MOS and varies depending on the proximity of the emitters and sensors in the transmitter and receiver. Some small objects may go undetected if entering the field between the individual beams. Picture finger tips passing through an open window blind—the left-to-right slats of the blind are analogous to two adjacent beams of light. There is a distance between the beams where a small object (possibly even an operator’s fingertip or hand) can enter the sensing field without detec- tion. The MOS defines how small of an object always will be detected by the light, regardless of where it enters the sensing field.
Additionally, most modern light curtains enable the user to intentionally turn off, or blank, a portion of the curtain. This allows chutes, conveyors or other items pass through the sensing field when required for production. Light-curtain manufacturers publish the MOS of their devices with no beams blanked, and the increased MOS that results with one or more adjoining beams blanked. The ultimate MOS will result in an additional distance the light must be moved away from the hazard beyond that defined by the formula used to calculate the safe distance.
Industry experts, to account for the fact that MOS varies, developed the Depth Penetration Factor as a way to calculate the additional distance the light’s sensing field should be
F—Vertical light curtains with horizontal remote segments pro- tect the front of the hazard. These photos were taken during installation; not shown is additional guarding added later to pre- vent reach from the feed side. An L-shaped barrier extends from the right side so that the part-escapement hole allows tall parts to escape while still being far enough from the line of hazard to protect the operator. This requires the use of a conveyor to bring the parts from the tool out through the guard.
Note: All barriers mount on heavy wall 8-in.-square posts anchored to the concrete. Mesh barriers comprise 1⁄4-in.-thick perforated-steel panels.
from the hazard to safeguard the operator. The end user must first define the line of hazard—the point nearest the operator where the action of the press creates a hazard. The light-curtain installer, then, places the curtain’s sensing field at least as far from that line as the safety distance calculated
46 MetalForming/February 2018
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