On the Development of Protective Devices for Bending Presses

Brake presses are machines which are widely found in the manufacturing industry. They enable metal sheets and plates to be bent in multiple ways so as to shape a wide variety of parts. The very principle by which these machines function creates a pinch and crushing zone for operators notably as far as their hands and fingers are concerned. In the last 30 years work both at the research and industry levels has sought to develop protective devices to protect workers from these hazards. This paper recounts research projects conducted in the last 30 years at École de Technologie Supérieure (ETS). Historically, the first publication, a research report, described the state of the situation in the 1990s in terms of safety of brake presses found in the transport equipment and machine manufacturing industry in Quebec. It was found that a small percentage of the brake presses surveyed were properly equipped with adequate safety devices. The research showed a number of problematic situations arising in industry such as complex shapes (for example, cones, tubes, boxes with multiples bends) which render use of protective devices available at the time difficult and even unfeasible. Furthermore, it was shown that accessories such as supports for workpieces and back gauges can contribute to safety. To address the issue of the low prevalence of protective devices on brake presses, a research project was undertaken to study the feasibility and applicability of light curtains on these machines. The study showed that the mode of operation of the light curtain as well as the geometry of the workpieces were crucial factors which determined the feasibility of light curtains as effective protective devices on brake presses. Difficulties in using these devices in certain cases were uncovered. A further research project sought to develop a different and more flexible protective device on brake press to alleviate these difficulties. The concept was based on computer vision. A bracelet was to be worn by the operator. A system of cameras captured images of the operator’s hands and a computer algorithm calculated in real time the position of the hand with respect to a defined hazard zone. The concept was proven to be effective. Computer time needed to be shortened in order to make the system feasible in a real setting. Machine safety needs also to be addressed from a risk assessment and reduction viewpoint. A research project thus sought to develop a risk evaluation methodology based on fuzzy numbers. This approach addressed the issue of lack of reliability both machine and human-related in assessing probability of occurrence of hazardous events. A risk reduction methodology was also developed which helps to identify action priorities in an analytical way. Further work is needed to tackle various issues such as field study to assess the state of brake press safety advances in the last 20 years, study of novel technology as protective devices such as smart gloves as an extension of the previous work mentioned herein and validation of fuzzy methodology in particular in relation to human reliability.