Factories contain numerous hazards, such as rotating cams and moving levers. Without any protection, personnel are directly exposed to these hazards, making accidents highly probable. Adding protective devices, such as protective shields to isolate moving parts from personnel, can effectively reduce accidents, but it cannot completely prevent them, as these devices can still be removed or opened.
To prevent such situations from occurring, a device linked to the equipment can be added to the protective cover. Firstly, the equipment cannot start if the protective cover is opened or removed; secondly, even if the equipment is running, it will stop immediately if the protective cover is opened. This is a safety interlock, a widely used technical measure for controlling hazards in the field of industrial safety.
Deconstruction of the definition of "interlocking"
Interlocking refers to mechanical, electrical, or other types of devices used to prevent dangerous machine functions from operating under specific conditions (usually when protective devices are not closed).
Figure 1 shows a common type of cam-based interlocking device. The number 3 , representing a special mechanical stroke, functions as the actuator. When the protective device 1 moves to the left, actuator 3 triggers the execution system 5 , and simultaneously, the output system 6 responds. The entire assembly 2 , composed of 3 , 5 , and 6, constitutes a standard interlocking device.
Four categories of safety interlocking devices
EN ISO 14119 , "Safety of machinery - Design and selection principles for interlocking devices connected with protective devices", is currently the only standard applicable to the use of protective devices and interlocking devices in conjunction with machinery, replacing the original EN 1088 as the harmonized standard under the Machinery Directive 2006/42/EC .
In view of the more advanced interlocking devices brought about by the advancement of science and technology, EN ISO 14119 has abandoned the classification in EN 1088 and generally divides interlocking devices into two types: mechanical interlocking and non-contact interlocking, and then further subdivides them into types 1 to 4 according to whether they have coding .
Both Type 1 and Type 2 are mechanically driven interlocking devices. Type 1 interlocking devices are activated by triggering a cam, which can be triggered by almost any solid device, so it is not a coded switch. Type 2 interlocking devices, on the other hand, have coding requirements. Generally, this type of switch has a special locking tongue, which can be imagined as a key. Only locking tongues that match the operating head structure can open the interlocking device.
For example, Pilz's mechanical safety switch PSENmech belongs to the Type 2 interlocking device. PSENmech consists of a body unit and an operating head. The latch has a special shape to trigger the switch body. Ordinary rulers, blades, or other similar objects cannot correctly trigger the switch. The contacts conform to the forced disconnect structure. Therefore, it is a mechanical contact switch with coding.
Type 3 and Type 4 are both non-contact interlocking devices. The example of the triggering principle of Type 3 interlocking device lists common non-contact sensing devices such as electromagnetic, capacitive, and ultrasonic sensors. Since they are non-coded, the form of the operating head is not unique. Although Type 4 interlocking device is also a non-contact switch, it needs to be triggered by a magnet, RFID , or other operating head with a certain code .
For example, Pilz's PSENcode contactless safety switch belongs to the Type 4 interlocking device category. The PSENcode series of safety coded switches are contactless switches based on RFID sensing. This RFID can achieve different coding types, and because it has coding capabilities, it belongs to the Type 4 interlocking device category. PSENcode has a completely enclosed structure, effectively preventing dust and liquid ingress, making it suitable for applications with high cleanliness and hygiene requirements, and allowing for some installation deviation.
In addition to the concepts of mechanical, non-contact, coded and non-coded, the EN ISO 14119 standard also provides a detailed description of safety door interlocks with or without protective locking. Pilz will bring you content related to safety door interlock protective locking in the next installment of this series.
