Safety device

Application filed December

To all whom it may concern: ... .,..: ,

Be it known that Γ, Robert L. Morrow, a citizen of the United States of America, residing at Meriden, ,Connecticut, have in5 vented new and useful Imp rove merits in Safety Devices, of which' the' following is a specification. .

My invention has for its object to provide means to prevent accidents, such as the loss 10 of fingers and hands, and the mutilation thereof, on machines and tools, such as. are in general use in mills and.factories throughout the country; a particular instance being power-driven circular wood-cutting, saws, 15 which are. responsible for a great many of these accidents. The attempts that have been made to overcome this problemwhave consisted usually in : providing mechanical guards covering the saw. which fail· of their 20 purpose, first, because they interfere with the view of the work, and are therefore oftefi removed by the operator; and second, because they do not guard the saw at the point where the work , is being cut, which is the 25 danger point; and often the worker pushes the wood up against the saw. with his thumb behind it, and loses the thumb before he realizes that he is hurt. .

The principal object of my invention is so to provide means'for preventing the' .worker from coining into contact With the saw or other tool, without interfering with'his view of the tool, or access thereto, of the feeding of the work; and 1 have found an 35 effective way to accomplish such object in providing means for giving a certain and unmistakable warning · of the. fact. that - his hand or other part of the body is approaching close to the danger point. A further 40 object of my invention is to give such warning before he has come: into contact with the dangerous moving parts of the machine and before he has been hurt; and.in such a way as to cause him instantly arid involun45 tartly to draw back from the source of danger. A further object of my invention is to give an electric warning by way of shock of burning sensation to the worker if his hand or any other part of his body ap³⁰ proaChes too close to the danger point,- the shock or burn being, of course, of such a nature as not to be harmful in themselves.

With these and other objects in view, my invention consists in the method, cbnstruc³⁵ tion, and combination and arrangement of <2 1,651,900 the accumulated charge. As soon as the circuit is broken, the core of the coil 11 be comes demagnetized, and the armature 12 closes the primary circuit again. This open6 ing and closing of the circuit takes place repeatedly in rapid succession, producing an oscillating current in the primary coil 13, which is transformed in the secondary winding 16 into a very high voltage oscil10 lating current, the voltage depending on the number of turns of wire in the secondary 16 in relation to the number of turns in the primary 13 and the voltage applied to the primary. The secondary 16 would 15 normally have thousands of turns. The terminal 17 of the secondary is connected, as directly as possible, to a conductor disposed adjacent the danger point, or preferably to the source of danger itself,— 20 as illustrated, the saw. Terminal 19 is suit_t ably grounded.

The potential is sufficient so that a spark will jump from the saw or other charged part of the mechanism a distance of about 25 2 inches, in practice, more or less, as the potential is varied, so that when the hand or other part of the body of the worker approaches the saw to within a couple of inches thereof, the saw immediately, gives ³⁰ out a spark and causes a shock and burn causing him instantly and involuntarily to withdraw his hand away from the saw.

The high frequency, high potential used is substantially that used by doctors in the ³⁵ treatment of various maladies, and when applied to the human body, the small amount of current which flows at the high frequency high potential has a beneficial effect rather than otherwise upon the body. 40 The potential being so high, the conductor leading it to the danger point must be carefully insulated, and it is desirable that it be short. As shown, I prefer to make the shaft 3 and flanges 2 holding the saw 45 1 thereon of non-conducting material. The shaft 3 may be provided with a shoulder against which one flange 2 abuts and the other may be held on and the saw clamped by means of a flanged threaded cap or sleeve 50 9, screw-threaded upon the end of the shaft, and between the shaft and the flanges 2 forming a seat for the latter. This cap or sleeve 9 is of conducting material, and is in contact with the saw 1, and may have ⁵⁵ formed thereon an exposed contact point 32 which projects outwardly and makes contact with a suitable fixed contact member 18 connected with the terminal 17 of the coil.

In order to provide a definite and effec⁶⁰ tive ground, the table is preferably covered by a metal plate 25, which extends to within about 2½ inches of the saw,, and is connected with a metal plate 26 on the floor surrounding the table on which the operator ⁶⁵ stands. The plates 25,i 26 are connected electrically, as by wire to the negative side of the high frequency coil.

While I have described my invention as applied to a wood-cutting saw, it is to be fully understood that it is applicable to ⁷⁰any form of dangerous tool where a high frequency high potential can be maintained at or near the danger point and insulated from the ground.

The operation of the device is as follows: ⁷⁵

When the saw or other tool is started up for use, the current is also caused to flow through the primary circuit 21, 22, causing the interrupter 12 to operate in the manner described, so that a high frequency, high ⁸⁰electric potential is induced in the coil 16, and led by the conductor 17 through the contact 18 to the contact point 32, and through the sleeve 9 to the saw itself, thus charging the latter with the high frequency, ⁸⁵high potential. This high frequency high potential is maintained upon the saw, without interference in any way with the working of the saw, and without hampering the worker in any way. The operator stands ⁸⁰upon plate 26 and in feeding the work to the saw his hand generally touches plate 25, both of these being connected to the negative of the high frequency coil; thus the operator is “ grounded.” If, and when, ⁸⁵his. hand or other part of his body approaches within a predetermined distance, say two inches, more or less, of the saw, due to the high frequency, high potential of the saw, a spark jumps from the saw to the ¹⁰⁰hand or nearest part of the body of the worker, giving him a shock or burning sensation which causes his muscles to involuntarily contract, and causes him to withdraw from danger on receipt of this warning and ¹⁸⁵before he is hurt.