1. Field of the Invention
The object of the present invention is an electric safety locking device adapted in particular, but not exclusively, to machines driven by an electric motor. It results from the ever increasing requirements related to the machine safety and from the difficulty, in some cases, to equip a detachable protective member with a locking device acting according to the principle of positive mechanical action.
2. Background and Material Information
In a locking with positive mechanical action, a moving mechanical protective member necessarily drives another member, by direct contact or by means of rigid elements. It makes it possible to ensure the functioning of the locking device under any circumstances, which is rendered necessary by the standards regulating the machine safety.
However, there are situations where it is impossible, or sometimes not desired, to have a direct action of the protective member on its locking device, precisely during its opening state corresponding to the dangerous situation, either because the opening position of the protective member results in the mere retraction thereof, or because the environment and the use of the machine render this direct action impossible, or for both reasons all together. In particular, this type of situation is very frequent in the field of cooking apparatuses where the protective members usually are lids that it is indispensable, for reasons related to hygiene and utilization, to be able to remove very easily and completely from their machine in order to clean them.
In such situations, an extremely simple electric safety device includes using, for example, either a magnetic switch, so-called FLS (flexible leaf switch, or REED switch), or a Hall effect detector, then constituting a magnetically controlled electronic switch, or a conventional mechanically controlled hard contact switch whose opening, in the absence of the protector, is ensured by an auxiliary mechanical element, such as a spring, for example, or by the effect of gravity forces, or by any other means. In each of these cases, the switch is linked to the frame of the machine and is closed under the effect of a magnet for the two first cases, and of an adapted mechanical element for the third case.
The magnet or the mechanical member are linked to the protector such that they cause the closure of the switch only when the protector is in its safe position. The opening or retraction of the protector cause the re-opening of the switch, except in the case of failure thereof, which results in the machine being stopped. These three types of switches are widespread.
However, they are not the only ones available for use. There are other devices that make it possible to detect the presence of the protective member, and to permit the operation of the machine. One can cite, for example, the inductive sensors, the optical or infrared systems, or the systems with an oscillating coil.