The primary goal when designing a machine has always been to make its automation process as efficient and cost-effective as possible to complete a task. With their more stringent requirements, safety controls are being held to similar expectations when being integrated into the machine controls. Safety control devices have evolved over the years and now play a crucial role in the interaction between man and machine.
What was once an afterthought, safety aspects can be implemented during the design phase by machine builders and added to older existing machines by end-users. The challenge with implementing safety at any stage of a machine lifecycle is making sure that the safety system is as effective and efficient as possible.
Making safety seamless and user-friendly
The automation process behind the scenes of mid to large machines can be intricate while providing a simple means to operate the machine via a Human Machine Interface or HMI. This allows a complex automation process to be seamless and user-friendly. Safety too can be seamless and user-friendly. The first approach would be to minimise hazards by design. If feasible for the machine and its application, this may reduce the cost of safety since fewer safety components may be required.
If, as in many situations, a hazard cannot be reduced or eliminated purely by design, or if further action is required, safety devices can be integrated. These could include guard monitoring devices that will prevent a machine cycle while a guard is open or presence sensing devices, such as light curtains or safety mats, that will detect an operator.
Integrating safety efficiently
Once a risk analysis is completed to determine what hazards need to be guarded and to which degree of circuit reliability, the question then becomes how to integrate the safety efficiently. As stated earlier, the automation design may be complex throughout the machine, with many components requiring communication to ensure the process runs smoothly. In many instances, this communication takes place in a network protocol that allows data packages to be exchanged throughout the system and can even be visually displayed on a control panel. Safety devices have evolved where they too can be placed on such a network. Knowing immediate information, such as which guard door is open, which E-STOP has been actuated and which safety device has faulted out, can drastically decrease downtime and thus increase productivity. An added advantage to most electronic safety devices is that they can be wired in series without reducing the integrity of the safety circuit.
Many manufacturers of safety devices can allow their devices to communicate on dedicated protocols, such as PROFINET, EtherNet, CANopen and DeviceNet, to name a few. In some instances, a manufacturer may require a gateway to convert their proprietary form of communication to one of the common industrial protocols, allowing a uniform data stream of safe and non-safe information. Another available protocol to use is the Actuator Sensor Interface or AS-i protocol. One of AS-i’s key features is that it is an open language allowing machine builders and end-users to easily mix and match different manufacturers’ AS-I devices and components to meet their various application needs. Another advantage of an AS-I system is its easy wiring which only requires a four-pin snap-on along with any point of its flat cable, greatly reducing the costs in installation time.
Making safety effective and efficient
With these types of technology, safety components no longer need to be completely isolated from the automation system. As an interlock device triggers a safe shutdown, it can send information through a PLC to bring a machine tool to a home position, all while showing its activity in a graphical representation on an easy-to-read screen at an operator station.
The increased efficiency in troubleshooting can easily be seen when this technology is compared with conventional electromechanical devices on mid to large-sized machines. Each access guard needs to be examined individually to determine which is preventing a machine restart when using electromechanical devices. The use of some of the advanced electronic safety devices can quickly and easily inform the operator of a specific fault through integrated LED lights and serial diagnostic signals.
Properly designed and installed safety systems within a machine are no longer a hindrance to the overall process. Education in safety provides a greater understanding and appreciation for its use, and technological advancements make safety implementation easier. The current capabilities of safety devices allow them to be used both effectively and efficiently.