Few barriers between humans and machines would be the desired position. But in many applications, the required safety must be guaranteed using movable guards while always keeping an eye on production efficiency. Safety gates, as an automation solution, including management of access permissions (via a ‘digital key ring’), represent safety concepts that offer both: protection and efficiency.
But what does ‘required safety’ mean? As a first step, users should weigh up the protection or safety gate monitoring they actually need because there are a variety of solution approaches available, both for safeguarding an accessible safety gate and for monitoring maintenance flaps, ie, non-accessible gates, for example.
For users, against tampering
Whichever safety solution one uses, it must be accepted by their users, otherwise tampering is inevitable. Userfriendliness is limited unnecessarily if safety is oversized. It’s exactly this issue of ‘defeating safeguards’ that’s a key aspect of EN ISO 14119. The standard defines guiding principles for the design and selection of safety gate systems and offers practical guidance on preventing tampering. It divides interlocking devices into categories, distinguishing between four types. There are types 1 and 3, ‘Interlocking devices with uncoded actuator’, requiring additional protective measures against tampering. There are also types 2 and 4, ‘Interlocking devices with coded actuator’, used most frequently. Mechanically operated position switches belong to type 2. A coded actuator is a specially designed actuating element that belongs to an assigned switch. The type 4 devices include coded magnetic sensors or sensors with RFID technology.
Coordinating safety components and solution
The standard’s excerpt already clarifies that the issue of ‘preventing tampering’ is closely connected to the respective application situation, and these are manifold. Therefore, much thought must be given to the type of monitoring and switch type appropriate for the specific situation or safety gate-type – swing and sliding doors, covers, flaps or rolling doors. Additional criteria concerning the actual installation situation must also be considered; whether space is critical, for example, or whether installation must be concealed or out of reach or whether environmental conditions are particularly rugged. Economic efficiency must also be considered, of course.
Dimension of protection: The basis
When the keyword is ‘economic efficiency’, ‘simple’ safety switches come to mind. Generally speaking, these are always an adequate solution when guard locking isn’t necessary to achieve the required safety for humans and machines. In other words, when machines don’t have a dangerous overrun and where basic protection is enough to guarantee sufficient safety.
These ‘simple’ devices can already master many application requirements without guard locking. They can be used to monitor the most diverse types of safety gates without incurring unnecessarily high costs. Various operating principles are available for selection, such as mechanical, non-contact magnetic or non-contact (fully) coded safety switches. Users can also select their dimension of protection in the Pilz PSEN sensor technology portfolio. If both humans and processes are protected, then mechanical safety switches PSENmech are suitable. However, additional measures must be considered during installation (positioning out of reach, concealed or screened). If maximum safety is to be combined with absolute economy, however, then non-contact magnetic safety switches PSENmag or PSENcode come into the frame, as they can also be concealed and can monitor the position of the guard as well as cover general position monitoring.
Hazardous overrun requires greater protective measures
ISO 14119 also specifies: an interlocking device must stop the hazardous machine movement immediately when the safeguard is opened and also prevent a restart as long as the safeguard is open. The question then is, when does an interlocking device with guard locking need to be considered? Whenever there is still danger from the machine after the stop command, i.e., when there is an overrun when machines have rotating knives or flywheels, for example, and on robots. The safeguard is not unlocked until the machine is in a safe state or has completely stopped; the safety gate cannot be opened until the machine no longer presents a danger.
So, whenever the machine still presents a danger after the stop command, ie, the machine still overruns, interlocking devices with guard locking come into consideration and safety guard locking devices, or even modular safety gate systems come into the frame. The latter enables a tailor-made solution. What’s more, with the appropriate expansions, they combine the requirements of safety and industrial security in equal measure, offering an adequate solution, particularly when the issue of access permission is to be considered – keyword: digital key or even keyring.
When process protection, when personnel protection?
Depending on the application, different operating principles can be used with respect to safeguard locking. The fundamental question here is: Are operating personnel to be protected in addition to the process? The distinction between conditional unlocking (personnel protection) and unconditional unlocking (process protection) is made. For pure process protection (i.e., preventing unintended interruption of the production sequence), guard locking in accordance with the open-circuit current principle is sufficient, for example. Guard locking is held in place by a magnet, which is deactivated again for unlocking. For example, this is an operating principle offered by the non-contact safety gate system PSENslock from Pilz. It combines safety gate monitoring with an integrated electromagnet and thus offers safe position monitoring with process guard locking in a single system.
Access calls for additional protection
Suppose operators are required to access a machine or can access it, and at the same time, hazardous overrun movements are still an issue. In that case, personnel protection must be considered in addition to process protection. This is where safeguard locking in accordance with EN ISO 13849-1 is required. The selection of the appropriate interlocking device is then based on the performance level (PL) determined by the risk analysis. In this case, safeguard locking can be achieved by means of the current closed-circuit principle.
In contrast to the open-circuit current principle, a spring is used to activate guard locking, while a solenoid coil is used to open the guard locking. Pilz’s mechanical safety gate system PSENmech enables this safeguard locking up to PL c; up to PL d with fault exclusion. These new electromechanical safety gate switches provide guard locking on the safety gate until the hazardous production process has ended and the plant or machine is stopped safely.
Alongside the current closed-circuit principle, the bistable principle equally ensures safeguard locking. This dual-channel operation of the guard locking only locks or unlocks when both channels have switched safely. It also detects faults such as short circuits, which cause the OSSD outputs (output signal switching device) to shut down but prevent the gate from being opened unintentionally, even in the event of a fault. Pilz implements this principle with the safety gate system PSENmlock, which can provide safe interlocking and safeguard locking up to PL e based on this technology. In conjunction with a controller such as the small configurable controller, the result is a complete safety gate solution, including comprehensive evaluation options.
Industrial security holds the key to safety
In contrast to safety switches, modular safety gate systems allow tailor-made solutions and combine safety and industrial security with the appropriate expansions. Such a ‘building block for safety gate guarding’ offers flexibility and decentralised intelligence for safeguarding a wide range of applications. These systems combine sensors, escape release and handles, as well as control and pushbutton units. The necessary components can be assembled to form an individual solution to suit the relevant application.
Such systems also offer added safety when they integrate access permission. They prevent safety measures from being defeated to (supposedly) make the work easier. Essentially these are intuitive operating systems that come into play here. Modules for access permission are integrated into modern safety gate systems to ensure that only authorised persons gain access to the application, i.e., safety gate monitoring and access control are combined, with industrial security included. It’s possible to ensure that only authorised persons have access to the plant-based on the qualifications and functions of the relevant personnel. Commands such as machine stop, unlock, lock or reset the machine can be controlled following successful authentication. That protects the machine from misuse or tampering and prevents unwanted downtimes.
Managing permissions centrally and efficiently
Together with the configurable safe small controller PNOZmulti 2, also from Pilz, the result is a complete solution that extends beyond safety gate monitoring. In combination with PITreader, it implements efficient permission management: users can configure access permissions for plant and machinery simply via “drag and drop”, using the corresponding software PNOZmulti Configurator.
Complex, hierarchical permission matrices can also be configured in the free user area. Staff members are permitted access to the plant or machine because their job or qualifications are identified. Depending on the company’s size, it may also be sensible to implement group-based permission management. In this case, the various enable are assigned not to individuals but whole groups with the same access rights. At the same time, access rights for a machine type used company-wide, for example, can be recorded and assigned centrally. All permission matrices are transferred to the RFID keys using the reader unit PITreader. This simplifies the assignment and administration of access permissions and, therefore, safety gate management, particularly for companies with multiple sites.
Safety gate with control for efficient access to machines
Modular safety gate systems lend themselves to complete gate applications. With comprehensive systems such as these, applications can be implemented flexibly and individually by combining individual components. If these modular systems also combine safety gate monitoring with access control, the result will be individual safety gate solutions, which efficiently manage access to the machine.
Courtesy: Pilz India