Electrical transmission or interconnection systems – Personnel safety or limit control features
Patent
1998-06-24
2000-05-09
Gaffin, Jeffrey
Electrical transmission or interconnection systems
Personnel safety or limit control features
361179, 361189, 324512, 324756, H03K 5153
Patent
active
060607963
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a protective circuit for monitoring an object which can move between two end positions, for example a displaceable safety door of an electric machine.
2. Description of the Background
From experience and according to the state of the art, protective circuits of this type are well known. Here, protective circuits are provided to monitor the displacement of an object from a first end position to a second end position by means of end switch activation. For example, this type of protective circuit monitors safety doors, safety grids, or the like, of electric machines such as presses, punching devices, milling machines, lathes and lifts. It has to be ensured that the aforementioned machines can only be operated after correct closing of the safety door or the like by means of appropriate switching devices, for example in order to avoid injury hazards for operators. Normally two-handed operation is required for switching the machine into the respective dangerous mode, which is supposed to ensure that both the operator's hands are busy and that it is impossible for example to reach into the dangerous area with one or the other hand. However, at the same time, it is to be made sure that the operator cannot enter the dangerous area with other parts of the body, like for instance his legs, or with his clothes. However, it is also possible that this type of machine is activated through one hand activation of a switch, particularly a push button, so that the operator's other hand might be able to reach into the dangerous area. For this reason, machines of this type have safety doors, safety grids, light curtains or the like, which only allow the machine to be operated when these components are either placed in the correct closed position (safety door or grid) or correctly switched on (light curtain). With such protective circuits, it is necessary that any manipulation of the object to be moved or the associated end switches and machine activating device be made impossible. Furthermore, it is desirable that the protective circuit works faultlessly so that only under these circumstances a connection with the consumer, i.e. switching on of the dangerous operating mode, is allowed, but that on the other hand, in case of kind of failure occurs inside the circuit, the connection is reliably avoided. Electric protective circuits known thus far either do not meet all safety criteria or they are so complicated and their construction so costly that they require very high expenditures and that the complexity of construction has in fact to be considered a safety hazard.
EP-A-105 054 presents a protective circuit for monitoring an object which can move between two end positions, for example a displaceable safety door of an electric machine with at least two end switches that monitor the end position of the object.
SUMMARY OF THE INVENTION
Starting from this state of the art, it is an object of the invention to provide a multi-purpose protective circuit for monitoring an object which can move between two end positions, which is of very simple and distinct design and which can consequently be produced economically, which also in particular cannot be manipulated, and the monitoring is designed so as to be independent of the start command.
To achieve this object, a protective circuit with the characteristics of claim 1 is proposed.
Consequently, the protective circuit mainly consists of at least two end switches monitoring the end positions of an object, at least one switch for activating a first reservoir for a first charge potential and an oscillator, in particular a multivibrator is connected to a known driver bridge which is connected to a consumer, for example the electric machine, the oscillator being linked to a second reservoir for a second charge potential which keeps the oscillator active for a predetermined period of time as long as the end switches are undergoing a change of state.
For a protective circuit according to the invention it is th
REFERENCES:
patent: 3947734 (1976-03-01), Fyler
patent: 4631722 (1986-12-01), Voss
patent: 4661880 (1987-04-01), Futsuhara
patent: 5081406 (1992-01-01), Hughes et al.
patent: 5345138 (1994-09-01), Mukaidono et al.
Klees Christoph
Schmitz Frank
Gaffin Jeffrey
Schneider Electric SA
Zura Peter
LandOfFree
Protective circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Protective circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Protective circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1067889