A compact access and control system has been developed that enables a selection of modules including mechanical trapped key interlocks, electrical safety gate switch interlocks, and electrical operator controls to be integrated into one unit. The system features patented mechanical and electrical connections between every module. It simply clips together and the internal network is self-configuring. With over 4000billion combinations of modules, it can be easily customised for every access and control application.
Wolverhampton-based Fortress Interlocks developed eGard after identifying a need for an intelligent, modular system for machinery guarding applications. The company has traditionally produced heavy-duty interlocking products for a wide variety of industrial applications, specialising in both mechanical and electromechanical interlocking. Its products are used in a diverse range of industries such as power generation and distribution, automotive manufacture, steel, pulp and paper, textiles and material processing.
The original concept behind eGard was to transfer the functionality of interlocking to medium and light-duty industry, an area dominated by lower-capability products than mechanical interlocks, such as simple tongue switches. Preliminary development focused on mechanical trapped-key interlocks and Fortress patented a mechanism for interlinking modular interlocks, paving the way for the new system.
Fortress then developed a range of heavy-duty modular, mechanical trapped-key interlocks, the mGard range, which consists of robust units which control access to enclosed areas. They can be used on their own or with up to ten multiple modules. This range features another patented sequencing system with up to 39,000 different sequences in a ten-module arrangement. Simple to configure, the units can be easily put together, or taken apart.
The company’s mGard range, consisting of door modules, bolt modules and key exchange modules, was then made available with rotary switches attached. When a key is inserted and turned the contacts on the switch are changed. The modules can, therefore, be used to isolate power, controlling access to potentially hazardous areas until a safe condition has been achieved.
The experience gained from the preliminary research and development, and subsequently the development of the mGard range, led to the development of eGard. Now the company’s thinking was to develop a modular system for medium and light-duty applications that went one step further than mGard and featured both mechanical and electrical functionality within every module, providing a complete, customisable access and control system.
The idea was a control system encompassing safe and standard I/O in one simple modular arrangement. The company wanted eGard to be easily fitted to any machine, with electrical connections at one end, minimising wiring. It had to be engineered for Installation Category 4 applications (the high-risk category defined by European machinery safety regulation EN954-1) and comply with international standards. It would be IP65 rated, polymer bodied for corrosion resistance and have stainless wear parts for long life.
The development process
The development process, as with any, produced a number of problems, but the sheer number of interacting parts proved to be a major complication. In addition, the company was used to producing products manufactured from alloys and stainless steel. This was the first product designed with polymer housings, so the design team had to familiarise themselves with polymers, snap fits and ultrasonic welding.
The company used Pro/Engineer CAD software for the mechanical design of the product, along with Pro/Intralink to manage the CAD data, allowing several designers to work on the concept at the same time. To ensure the final product would be affordable, the basic external polymer housing was designed to be exactly the same for each module, despite the fact that there are many different types of module.
Modules include mechanical locks, electrical locks, safety switches, service modules such as indicators and buttons, internal releases, emergency stops, and a selection of actuators suitable for both hinged and sliding doors. As the project advanced the polymer body and base went through many design variants before it was finalised. Now the basic modules can accommodate any type of standard controls such as switches, buttons and lamps, as well as trapped key and electrical interlocks.
The mechanical links utilise the patented mechanism from the first research and development project, although the links run down one side of the module rather than the spine as had been first planned. This allows the electrical connections to run down the other side of the module. The runner bar connects without having to be screwed together. It simply clips together and is then held securely in place by the screw tube that is used to install the product on site. The fixing holes are designed for aluminium extrusions, but the system can be simply fitted to any other machine or gate housing.
A fundamental innovation is a separation of ‘Safety’ and ‘Control’ information, within the PCBs. A set of hard-wired, dual-channel safety circuits is implemented on every module, to allow modules to be configured in any order. The dual safety circuits ensure the safety of the product by shutting down the system if there is a malfunction or Emergency Stop condition. An isolated internal data bus system had to be developed using a series of PIC microprocessors to convey control data. It is this internal network that controls the components such as the switches and lights.
The internal electrical connections were developed to ensure that the network uses a minimal number of terminals to relay the I/O information. The internal network is also self-configuring, for ease of installation and reconfiguring. Each module has a PCB, some with a processor, and at the end of the modular stack is a control module. The processor in each module is programmed to tell it what type of module it is, and the processor in the control module knows where each module is and what its address is.
There are three electrical end modules:
- Safety and Control module;
- Safety Only module;
- AS-interface module
(AS-interface, or AS-i, is a relatively new cabling system that allows machinery safety equipment, such as access gate switch interlocks, to operate in parallel with standard machinery controls on a single network with a common communication protocol).
A cap and Foot are also available if eGard is used for purely mechanical interlocking. With the correct selection of end module, eGard can simply connect to programmable logic controllers (PLCs) and mimic panels, or can be used on an AS-i network.
Developing the crucial software to handle the non-safety data took a great deal of time. In addition, space considerations were different within each type of module and the PCBs feature different components. Fortress was eventually able to design a module PCB with eleven variants that would fit and work within each module.
Fortress also had to develop a new electrical locking system, as space was very limited. In addition, power consumption was a big factor as eGard runs internally at only 5V and space is limited. In one version, power is applied to the solenoid to unlock the mechanical runner bar. Another variant can also work in reverse and when powered can lock the runner bar. These can be used to stop the insertion or release of trapped keys or the tongue from the head.
Fortress put eGard through a failure modes effects analysis (FMEA) to thoroughly test the product and look at how each module could fail. It is the best method for checking the interaction of all the components. This highlighted the problems, allowing the company to make improvements and refine the design.
Fortress hopes that eGard will revolutionise safety in medium and light-duty industries. The finished product’s innovative design, advanced functionality and ease of installation have already appealed to many companies seeking to ensure that their safety equipment exceeds current expectations.