Warning facility for bone bandsaws

Status:

completed 02/2008

Aims:

In the meat-processing industry, clean bones and meat cuts (such as ribs and chops) with a bone component are cut up manually at high speed with the use of bone bandsaws. In the process, bandsaws repeatedly come into contact with the user's thumbs or hand. Severe irreversible injuries occur as a result. In close consultation with the institution for statutory accident insurance and prevention in the meat-processing industry, a visual warning facility was to be developed and tested which detects the user's fingers in the area +/- 2.5 cm around the saw blade and 15 to 20 cm in front of it, and generates a warning (light signal). The bandsaw was to be switched off only following several violations of the safety zone in the course of a shift. The warning facility was to be combined with a laser which makes the critical danger zone ahead of the saw blade visible. In its commercial implementation, the warning facility was to be implemented in Category 2 to DIN EN 954-1: "Safety of machinery - Safety-related parts of control systems - Part 1: General principles for design".

Activities/Methods:

The first step involved analysis of the temperature conditions on the bandsaw by means of an infrared camera. Different working methods (with gloves, chain gloves, without gloves) and meat temperatures were taken into account. Based upon this analysis, an algorithm was developed for recognition of the hand by means of a passive infrared sensor. The signals were evaluated in a low-cost microcontroller housed in a water-tight enclosure (IP 67). The laser used for demarcation of the warning area was developed by an optical company. The infrared sensor and the laser were to be combined in an enclosure and tested in routine operation.

Results:

Infrared imaging revealed that detection of the hand solely by means of a sensor which responds to the thermal radiation is not possible during work, owing to the use of well insulated gloves. For this reason, a sensor system was developed which is capable of clearly detecting the workpieces at the bone bandsaw in the near infrared range. This enables the workpieces to be distinguished clearly from the gloved hands of the user. False alarms were triggered during work with bare hands, however, since they could not always be distinguished clearly from the material to be processed. For this reason, an infrared sensor was employed in addition which enables the unprotected hands to be distinguished from the material to be processed on the basis of their temperature. As a laboratory prototype, this sensor combination delivers promising results. Following the project, the laboratory prototype is to be developed further by a manufacturer of protective equipment.

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