What Are Machine Safety Devices?
Machine safety devices protect operators from mechanical hazards that can cause harm and injury when working with machinery. Examples of dangerous equipment include mechanical presses, CNC machining centers, robots and moving machinery. You use safety devices together with machine guarding to ensure no one can access machinery except through the correct point of operation, which is protected by a safety controller.
Critical Aspects of Machine Safety Devices
Critical aspects of machine safety include reliability and a fail-safe design. This ensures machinery can only be activated when it is safe to do so. Manufacturers carefully engineer machine safety devices with robust components to ensure long-term reliable operation. A particular aspect is ensuring that the design of safety devices is fail-safe. This means that if a component fails, for example, if a contact welds, the device reverts to a safe mode and will not allow machinery to operate.
This is why safety devices cost more than standard devices.
Types of Machine Safety Devices
One of the most common types of safety equipment is the two-hand control actuator. These devices keep machine operators’ hands safe from the risk of inadvertent contact with moving machinery. Other safety devices include light barriers, safety interlocks, safety relays and controllers.
Light Barriers
There are two types of light barriers: the safety light curtain and laser-operated safety scanners. A light curtain has two components: a transmitter and a receiver. Type 4 curtains intended to protect fingers and hands have a beam spacing of approximately 14 to 25 millimeters (between 0.5 and 1 inch), while type 2 light curtains use a wider spacing of 30 mm (1.18 inches). If anything interrupts the light beam, the controller disables the machine controls.
A laser scanner works on a different principle. It transmits a rotating horizontal laser light beam that detects movement within a predetermined danger zone. It does this by measuring light reflecting off personnel or equipment within the zone.
Safety Interlock Switches
Safety interlocks protect machinery access gates by preventing the operation of machinery if someone opens an access gate or tries to access moving conveyor belts. Some safety interlocks incorporate a lockout function that requires a manual reset by the operator.
Safety Controllers
Safety controllers form an integral part of machine safety control systems. They allow engineers to program safety equipment and link multiple safety devices into one controller. A safety controller operates like a PLC but incorporates special safety logic protocols and high-level reliability components.
Safety Relays and Contactors
A safety relay is a multiple-contact mechanical relay operated by a safety device. The relay incorporates a mechanical linkage that prevents operation if one or more contacts fail. Safety contactors follow the same principle, except the contact rating is higher for power transmission. Some manufacturers color their safety relays and contactors yellow to distinguish these devices from standard relays and contactors.
Why You Shouldn’t Use Standard Relays and Controllers as Safety Devices
Standard relays and controllers don’t have the same built-in safety mechanisms that prevent operation in case of a component failure. Also, they don’t necessarily have the same level of reliability nor a guaranteed number of rated operations, a factor that’s crucial with safety devices that must reliably operate every machine cycle. Using the right type of machine safety equipment is crucial for safeguarding machine operators and other personnel.