Even with a thorough management system, unexpected accidents can happen. It is difficult to completely prevent accidents and troubles simply by educating workers and engineers to ensure thorough safety management. What is important here is not only human safety management, but also "aiming to establish safety by machine". This time, we will introduce the safety management of machines along with the "safety categories" that are deeply related to machine control systems.
About "safety category" to see how safe a machine is
"Safety category" is an indicator of safety measures based on the results of risk assessment. The safety category is divided into five levels, B, 1, 2, 3, and 4, from the bottom, and the feature is that the required safety functions become stricter depending on the level. Below is an overview of each safety category.
Safety category B
Safety Category B requires the realization of the basic functions of the machine control system. Of particular importance is durability against environmental stress. Corrosion by chemicals, interruption of control circuits, stress caused by mechanical vibration, etc. must be addressed. Since it is the most basic category, it is quite possible that safety functions will be impaired if any defect occurs in a machine of Safety Category B.
Safety category 1
In addition to meeting Category B requirements, this is the stage where more reliable safety functions are required. For example, we are required to introduce parts that have been used in a wide range of applications and that have been confirmed to be highly reliable and safe. A Safety Category 1 machine that meets this requirement has a lower probability of damage to the safety function due to failure than a Category B machine.
Safety category 2
As with Safety Category 1, it is required to meet the requirements of Category B. At the safety category 2 stage, inspection equipment and inspection result output functions are required. It should be designed to allow safety checks within the machine at appropriate intervals. If the inspection function performs normal checks when starting the machine or when a dangerous situation occurs, the machine meets the requirements of Category 2. However, any failure between checks could result in a loss of the safety function of the entire machine.
Safety category 3
In addition to meeting the requirements of Category B, this is the stage where conditions such as "a single defect must be detected" and "safety functions must not be impaired even by a single failure" are required. By satisfying this condition, the safety function operates properly even in the event of a single failure, so the machine maintains a high degree of safety. However, it is possible that undetected faults accumulate in the machine and adversely affect safety functions.
Safety category 4
In addition to meeting the requirements of Category B and following well-examined safety principles, fault detection capabilities exceeding Category 3 are required. It is necessary to design so that the safety function is always maintained even if some failure occurs. By fulfilling this condition, faults in the machine can be detected in a timely manner, and minor and serious hazards that may affect the surroundings can be prevented before they occur.
Machine safety functions and control systems are built around these safety categories. In order to minimize the damage caused by unexpected accidents and failures, indicators represented by safety categories are necessary.
Safety education for workers and engineers is extremely important, but the current situation is that it is difficult to establish a high level of safety with that alone. The safety category is an important indicator for ensuring safety through machine control. By introducing and operating machines with a high level of safety category, it is possible to create a workplace that does not rely on human safety management.