Safety doors are primarily used to prevent machinery from operating under specific conditions (usually referring to situations where the safety device is not closed) to minimize the risk of danger. If the safety door switch itself is not installed correctly, causing its interlocking function to malfunction, this "failure to act when it should" is clearly undesirable. Therefore, the first priority when using safety switches is to use them correctly.
Requirements for fixed safety switches
Proper installation is a prerequisite for ensuring the normal functioning of safety switches. Here are some requirements for installing fixed safety switches:
Fasteners themselves need to be reliable and stable enough.
Specialized tools are required for removal, such as hex screws or star screws. Phillips head screws / slotted screws are not recommended because in some cases, these screws can be easily opened with a fingernail or personal equipment.
Fasteners need to be prevented from coming loose on their own, and when appropriate, the need for elastic washers or screw glue should be considered.
It is necessary to prevent damage caused by foreseeable external impacts, and the installation location should be determined according to the actual situation, such as away from the horizontal surface where people walk and forklifts frequently pass.
Mechanical switches need to be operated within a specified range, especially mechanical latches, whose length is fixed. If the installation distance is not calculated properly, frequent operation can easily cause physical damage to the switch.
Safety door switches are not permitted to function as mechanical stops or barriers for protection. This is also to avoid damage to the switch body and operating head, minimize unnecessary physical impacts, and prevent safety malfunctions and reduced service life.
Safety doors are primarily used to prevent machinery from operating under specific conditions (usually referring to situations where the safety device is not closed) to minimize the risk of danger. If the safety door switch itself is not installed correctly, causing its interlocking function to malfunction, this "failure to act when it should" is clearly undesirable. Therefore, the first priority when using safety switches is to use them correctly.
In practical applications, some operators, for the sake of convenience, intentionally leave the safety switch constantly signaling even when the safety protection is open. For example, they might attach an extra operating head to the switch body, rendering it inoperable. To eliminate safety hazards caused by improper operation, the ISO 14119 standard specifically describes "supplementary measures to minimize the possibility of obsolescence of interlocking devices," which are the safety switch anti-shielding measures we often refer to.
Main measures to prevent shielding of safety switches
The physical location of the installation is "out of reach or visible but not touchable".
Consider installing components in places inaccessible to personnel, or directly installing protective covers on the outside of the interlock switch to prevent disassembly or movement, as shown in the figure. Whether it is a mechanical interlock in the left figure or a non-contact interlock in the right figure, there is a chance to prevent it from being shielded by protective covers.
Installation physical location – “invisible”
The interlocking switch itself is installed in a concealed manner, making it difficult to identify and disassemble.
Its inherent anti-blocking capabilities – “high coding level”
Is it possible to improve the shielding capability of the safety door switch components themselves?
As shown in the diagram below, depending on the product characteristics, such as general mechanical latch-triggered switches, ordinary magnetic switches, and hinge switches, they all belong to the low coding level, and their operating heads can have 1 to 9 different coding variations. For high coding levels, more than 1,000 different coding variations can be achieved. For example, the PSENcode series of unique coding type switches only require the operating head to sense and identify the corresponding switch body.
For high-risk situations, high-coding-level switches can be selected. If medium- or low-coding-level switches are still required in high-risk situations, additional protective measures will be necessary.
Additional measures to prevent shielding of safety switches
In addition to the previously mentioned measures of selecting appropriate switch installation locations and switch coding levels to minimize the possibility of obsolescence of interlocking devices, selecting non-removable fasteners or securing methods is also an option to consider. For example, using covers or permanent fasteners (such as welding, adhesive, one-way screws, or rivets) for protection.
Of course, choosing a suitable safety controller can also serve as a means of preventing shielding in certain situations. For example, pre-embed some state tests and periodic tests in the logic, and once the monitoring detects an anomaly, it will stop the dangerous movement of starting the machine.
