An evaluation of machine guarding techniques for robot guarding
Abstract An increasing number of problems caused by the use of industrial robots should be expected due to the dramatically increasing population of robots today. In this paper, machine guarding functions and techniques are reviewed. The possibilities of transferring the concepts of machine guarding to robotic systems are then analyzed. The analysis shows that most of the guarding techniques are still applicable to industrial robots with modifications to accommodate differences. A set of guidelines for installing safeguarding devices is also presented. Research is need in the areas of guarding techniques for robotic cells, new sensor development, and sensor reliability, fusion, and coordination problems.
Theory and application of a capacitive sensor for safeguarding in industry
A capacitive sensor for the safeguarding of automatically working machines in industry has been developed. It can be used as a complement to more expensive pressure sensitive mats, light curtains or fences. The sensor consists of two electrically conducting planes, insulated electrically from the ambient. The planes are placed opposite each other, one in the floor and one in the ceiling of for example a robot cell. One of the planes is used as the antenna of the transmitter and the other works as the antenna of the receiver. When conductive conditions in the space between the two planes are altered, e.g. a person enters, the signal from the receiver changes and indicates the presence of the person. By the use of a current/voltage-converter followed by a lock-in amplifier as receiver an excellent signal-to-noise ratio is achieved. A sine wave modulated by bandwidth limited white Gaussian noise is used as transmitting signal. This signal reduces the strength of the electric field per frequency unit, radiated by the sensor. The theory for the sensor and the sensor signal handling is presented and some practical experiments are described. The theory is well verified by the experimental results.<<ETX>>
One hundred percent tumor induction in mouse skin after repeated beta irradiation in a limited dose range.
Repeated beta irradiation of the backs of mice three times a week with radiation doses of 250 to 1180 cGy per exposure induced 100% incidence of tumors. The incidence of skin tumors appeared to be determined by the total number of repeated exposures in this dose range. An abrupt delay in tumor emergence was observed when the radiation dose was reduced from 250 to 150 cGy per exposure, indicating the existence of a critical threshold. Mouse skin resembles human skin rather than rat skin in its response to radiation.