Advanced Safety Mat Guarding

Uniform activation provides a guarding system that contains no dead zones, giving the user a much safer guarding system.

• By F. Gary Kovac
• Jan 01, 2004

HAZARDOUS areas in manufacturing facilities require a device to protect workers from injury. A popular machine guarding solution is a safety mat system that, when stepped on, initiates a stop signal, preventing injury that may be caused by a piece of hazardous equipment.

Used in safety mats for machine guarding, the Soft Tactile Transducer Sensor (STTS) completes a system creating a hybrid design that combines features to meet and surpass both domestic and international safety standards. Through state-of-the-art design features, this flexible technology sets a new standard for presence-contact sensing and machine guarding. The product and technology was designed to overcome the previous problems of rigid electrode (steel mats), such as rusting, denting, puncture by tools or objects falling onto the mats, shorting out, and limitations on customized sizes and shapes.

STTS mat technology is a tactile sensor that provides information regarding the distribution and magnitude of tactile force applied to its surface. This patented technology involves the continuous and variable measuring of tactile forces of pressure. In some respects, tactile sensing for electro-mechanical devices is analogous to the human sense of touch--information about the amount and distribution of tactile pressure over a surface can be received and transmitted. When an object comes in contact with the sensor, tactile sensing provides information about the object's shape, texture, position, orientation, deformation, center of mass, and presence of torque or slippage. This technology can be applied in any application that requires reliable, intelligent monitoring.

Industrial safety applications benefit from the STTS system's unique capabilities. Safety mats can be homerun wired back to the controller and are continuously pulsed. The mat and wiring is routed through a unique, built-in wire raceway system. This verifies that each safety mat is wired properly and is connected to the mat controller. Unlike open-switch rigid electrode mat systems, the STTS technology pulses and monitors the mat itself. This verifies that the mat wiring has not been bypassed, jumpered, or shorted outside of the control box and prevents against an automatic reset of the control (green) with a disconnected mat system.

Each mat in the safety system is automatically assigned a specific value and address by the controller and must be recognized and verified as the controller monitors the safety zone. This continuous pulsed monitoring system provides a higher level of safety mat guarding. The pulsed system eliminates the possibility of wire tampering or jumpering out of safety mats versus open-switch non-pulsed systems.

The mat safety system should provide an activation threshold (on/off signal) throughout the entire mat surface area. Uniform activation also provides a guarding system that contains no dead zones, giving the user a much safer guarding system.

Uniform activation means that the safety mat has no dead zones on the mat surface--it is 100 percent active.

This new technology also can create an "Intelligent Mat." Traditional safety mat guarding with the addition of a pressure-activated, "on/off" controlled switch sensor, for areas based on force/area (psi). An "Intelligent Mat" provides a broad understanding of the kind of tactile event that is occurring and, in the same way as the standard mat, is scalable because of its analog output and natural psi characteristics. What makes the "Intelligent Mat" unique is that it can be programmed by varying the electrode pattern to determine where the contact has occurred on a multiple position basis (in width "x" and length "y") and the basis of mass point loading ("z").

The STTS technology provides safety mats with an active edge, enabling the user to place the mats side-to-side or end-to-end. Simply sliding an active coupler in place solves cumbersome multiple mat installation problems normally associated with mats. It also eliminates the need for thresholds, closeout, and uniting strips that create dead zones, which increase substantially both product costs and installation time.

By providing greater sensitivity and uniform activation, the STTS technology enhances machine-guarding options. This true and uniform activation threshold is unobtainable with "force-style" mats. Safety mats normally utilize insulators within their switching element as standoffs and around their perimeters as seals. These standoffs or insulators create dead zones and require large amounts of force to activate the mat in that particular area.

STTS technology is providing safety engineers with added flexibility. A modular system can be designed specifically for a project. Equipment can be safely guarded even in the toughest of applications in an efficient and cost-effective manner.

The minimum distance from the danger zone shall be calculated by using the general formula:S = (K x T) + CS is the safety mat minimum distance in inches/millimeters in a horizontal plane, from the danger zone to the detecting edge of the safety mat furthest from the danger zone.

K is a parameter in inches/millimeters per second, derived from data on approach speeds of the body or parts of the body. K = 63 inches/second, or 1600 mm/second.

T is the total system stopping time performance, which includes activating the safety mat, the mat controller output signal-switching device, and the time required to stop the machine and remove risk.

C is an additional distance in inches/millimeters, based on intrusion toward the danger zone prior to actuation of the protective safety mat equipment. C = 48" (1219 mm).

This article originally appeared in the January 2004 issue of Occupational Health & Safety.