Electricity: motive power systems – Braking – By auxiliary electric generator or by magnetic attraction or...
Patent
1983-06-03
1985-07-09
Dobeck, B.
Electricity: motive power systems
Braking
By auxiliary electric generator or by magnetic attraction or...
83DIG1, 83522, 340680, 318490, H02P 300
Patent
active
045284881
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention concerns a safety drive for a working machine driven by an electromotor and displaying a moving tool which is potentially hazardous, as well as a input shaft for the tool, an electromotor with an output shaft, a drive mechanism connecting the output shaft with the input shaft, and a switch to activate the electromotor.
The invention was designed particularly with a view to its application in circular saws, but can also be employed for other tools, for example, electric lawnmowers which operate with a rotating blade.
UNDERLYING STATE-OF-THE-ART
Machines of this type, some of which are equipped with very quickly rotating tool parts, present the danger that after the electrical drive motor is shut off the tool will continue to run for some time, which may result in bodily injury when the tool is handled without due caution. The most recent safety regulations therefore demand that, for example, the circular blade of a table-top circular saw must come to rest within 10 seconds after the machine is shut off.
To be sure, there is no lack of technical solutions intended to fulfill this demand; in reasonably priced work machines, particularly for household work, the incorporation of these costly technical measures can affect the price at which the machine is sold. In the production of these machines an attempt is made to largely employ moderately priced, serial components, which applies particularly to electrical drive motors; these components are selected from marketable standard series and are produced in accordance with all the new technical requirements, thus generally causing a sizeable price increase.
DISCLOSURE OF INVENTION
The objective of the present invention is, therefore, to create a safety drive for a work machine driven by an electromotor, which safety drive fulfills the demand that the tool part have a short overrun period once the motor has been shut off, and which can be constructed from the simplest and most conventional components.
This objective is fulfilled in a safety drive of the initially described type by an electric generator which is provided with a drive element and is positioned in the area of the drive mechanism in such a way that it can be engaged with the drive mechanism, and by an activating device connected with the switch of the electromotor, which device engages the generator with the drive mechanism when the switch is disengaged. In choosing the small generator, a series-produced, reasonably priced drive generator is preferred, which at the simplest would need to be equipped only with a clamp and a corresponding belt pulley for suitable interaction with a drive belt. In the case of circular saws, it is in general desirable for the the saw blade to extend beyond the table plate in order to assure the highest possible cutting level with the giving saw blade. This naturally demands that the axis of rotation of the blade, viewed fro the lower side of the table plate, can be brought as close as possible to the working surface of the table plate. This is hardly possible with a coaxial positioning of the electromotor, since in any case the motor must have a greater diameter than a belt pulley of minimum diameter on the tool drive shaft. The use of a belt drive is therefore of added advantage under these circumstances.
The warning light fed by the generator can be advantageously placed on the blade protecting bonnet of a circular saw, it being possible to use both the bonnet fastener and the splitting wedge as parts of the current line to the warning light. On the other hand, it is possible, as is the case with other working machines, to place the warning light directly in the operating handle for the motor switch.
In many working machines, including circular saws, it customary to design the activating element for the motor switch in the form of a stick-like switch lever whose upper end projects out of the machine frame. Under the invention it is possible to provide this switch lever with a corresponding activating rod, by means of which the moveably
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patent: 2564413 (1951-08-01), Vossen
patent: 2766416 (1956-10-01), Myles et al.
patent: 2969130 (1961-01-01), Logan
patent: 3109164 (1963-10-01), Happe et al.
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patent: 4132932 (1979-01-01), Morton et al.
Byrne John J.
Dobeck B.
Kile Bradford E.
O'Brien Kevin M.
Ro Bentsu
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