US 2944120 A
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Description (OCR text may contain errors)
July 5, 1960 2. D. RUBEN SAFETY FOOT SWITCH Filed June 12, 19 58 with the hands.
United States Patent Ofi ce 2,944,126 Patented July 5, 1960 SAFETY FOOT SWITCH Zorro D. Ruben, 54s Fern Ave, Elmhurst, Ill.
Filed June 1'2, 1958, Ser. No. 741,542
2 Claims. c1. zoo-s This invention relates to control devices used to start and stop electric motors and other power sources operating certain types of machine tools such as circular saws of the table or bench type, presses, routers or shapers and the like.
More particularly, this invention pertains to an electric motor switch for such machines, the control surface of which is placed near the floor to be depressed by the operators foot or knee when it is desired to start and run such machines. This action by the operator closes the circuit and maintains it closed as long as he maintains his pressure on the control, but, on releasing same, he opens the circuit and stops the tool.
A switch of the above type is generally known and referred to herein as a momentary contact, normally off switch. It is also called, in short, momentary, normally off or simply momentary.
For certain types of work, for example: when an operator must move away from the machine while it is running, it may be desirable for the circuit to remain closed when the operators control pressure is released. Switches meeting this requirement, with depressable control surfaces, are referred to herein, and generally known, as push on, push off switches or simply maintained contact push switches. This type of electric circuit control is depressed once to either close or open the circuit, which then remains either closed or open when the operato-rs pressure is withdrawn although the control surface returns to its normal position. Subsequently, when the control surface is thereafter again depressed, the circuit is thereupon changed to either open or closed respectively and remains so after the pressure is released.
This cycle, as is the case with the momentary switch, is of course indefinitely repeatable. V In other words, every alternate push on this switch either opens or closes the circuit.
These switches are referred to herein as manual switches to distinguish themfrom machine or automatically actuated switches although the word manual -is here to be taken in the broad sense to include human operation with a foot or knee as well as by hand.
The operation of tools by means of either one of the above mentioned switches, when placed on the floor and depressed by a foot or toe, provides one element of safety and convenience in that the cutting toolneed not be moving while the work is being brought into position Thereafter, the toe can start the machine withont necessitating the removal of a hand from the work.
The momentary switch presents an additional element of safety over the maintained contact type in that, in the event of an emergency requiring the power to be shut off, this switch will obviously work faster, since it merely requires a release or withdrawal motion which comes naturally in such an event.
lowing element of hazard when compared with a maintained contact, hand operated switch:
with the operators knowledge.
The operator or a bystander may accidentally step on, or slip, and thus depress the foot control at a moment when either may have his hands in contact with the tool. The switch could also be depressed accidentally by a falling object. For these reasons, foot switches are often provided with hoods to cover the control surface. However the hood in itself could not prevent the operators accidental exertion of pressure on the control if he should be pushed or otherwise lose his balance while his foot is over the control and under the hood.
It is an object of this invention to provide a momentary switch which will prevent the starting of a machine by the unintentional depressing of the switch through a single accidental slip, fall, or step.
It is also an object of this invention to provide a safety control which does not require a hood over the control surface and thus make it unnecessary for the operator to search for asmall opening with his toe or to look down to find the opening each time he must return to the machine after leaving it.
It is a further object of this invention to increase the portability of a control, and of tools using the control, by providing an equivalent and improved safety device without a hood, and of smaller dimensions and weight.
It is a still further object of this invention to provide a safety control which can be operated with a knee as .well as a foot while retaining the above-mentioned improvement in portability. This improvement is desirable whenever the tool itself must rest on the floor, and the operator is required to kneel, as in the installation of flooring.
According to this invention a control device is provided which requires of the operator 8. sequence of four motions, as indicated in the left hand column of the following outline, to start, run and stop a power unit each time after it has been run and stopped.
The right hand column of the outline which follows presents an electric control and circuit effect of each of the operators four motions as required to energize an electric motor to power a tool or other instrument to attain the objects herein.
Operators Motion Circuit Effect of Motion 1. Depresses the control surface from its normal position. Immediately thereafter he- 2. releases pressure from the con trol surface. Immediately thereafter he again- 3. depresses the control surface, 3.
this time starting the tool. He holds the control surface down as long as he wishes the tool to operate, whereupon he 4. releases pressure from the control surface until it is desired once again to start the tool.
1. Circuit remains open.
2. Control surface returns to its normal position automatically and circuit remains open.
Circuit now closes to start the tool motor and maintain it in operation until 4. circuit is opened and tool stops as control surface returns to normal position.
After stopping the tool with motion No. 4 above, the control is recycled with the No. 1 motion to start the tool again.
Motion No. 1 above may be caused by accidentally stepping on the switch in walking about, in sitting down, by slipping, or by a falling object. This would then normally be followed by motion No. 2 above, usually However no harm can havebeen caused to either the operator or the work as the motor was not started. If he does not desire to use the tool immediately the operator can hit the switch deliberately, momentarily (motions 3 and 4), and thus put the tool back on safety. I
It is conceivable, butunlikely, that an object of suf- .ficient weight to depress thecontrol could fall on and person almost invariably is unsatisfied that his first'depression of the control was complete and in trying again he then leaves the switch reset on safety as does the regular operator after each use of the tool.
Once acquainted with the need to depress or kick the switch twice to start, the-extra motion required of the operator consumes only a small fraction of a second.
The above and other objects, advantages, desired mode of operation, and features of the invention are realized in a preferred mechanism for an electric control described in the following specification and drawings where- Fig. 1 is a perspective top view of anelectric control in a normal position with itscircuitconnecting wires out Fig. 2 is a view from the end through which the wires enter;
Fig. 3 is a longitudinal section, showing a switch in view, taken along the 1ine'313 of "Fig. 2;
Fig. 4 is an enlarged side view, partly in section, of one of two known types of switches forming one element of the control;
Fig. 5 is an enlarged side view partly in section, of the other of the two'known types of switches forming a second element of the control;
Fig. '6 is a diagrammatic drawing of the circuit with the control surface depressed and both switches in the circuit closed position;
Fig. 7 is the (same) circuit diagram with the control surface raised in the normal position always subsequent to that of Fig. 6,'and with the circuit open;
Fig. 8'is the circuit diagram with the control surface depressed and the control in the open position always subsequent to that of Fig. 7, and
Fig. 9 is the circuit diagram with the'control surface raised and the control in'the open position always subsquent to'that'of Fig. 8 and preceding that of Fig. 6.
In the drawings the same reference characters indicate the same elements throughout.
A switch mechanism which will produce the circuit effects corresponding to the sequence of the fouroperators motions as set forth in the outline hcreinabove can be constructed most readily and economically with two commercially available switches, a simple housing, and one lever or control pedal common to both switches.
A push on, push off, maintained contact switch 1, and a momentary, normally off switch 2, are wired, in series, on one side of an electric circuit, between a power source and a motor, as shown in the diagram of Figs. 6 through 9. Switches of these types are known and commercially available. For example, both are currently made by Carling Electric, Inc., of West Hartford 10, Connecticut. In their catalog'C, publishedin 1956, their numbers 111- 16P and lll-PM-OFF are examples of switches 1 and 2 respectively.
Switches of'these types, ,as detailed in Figs. 4 and 5, are provided with threaded outer sleeves 3-3 on which hexagonal and ring nuts 4-4 and 5-5 respectively may be assembled. These are :usually placed on either side of a structural wall such as the wall 6 of a housing 7 on which they are thereby mounted. The sleeve, with one nut in place, is inserted through an opening 8 in the wall 6, following which, the second'nut may be screwed on the sleeve and tightened to the wall.
Some of the mechanical details of each switch 1 and 2 are indicated in Figs. 4 and 5 respectively. For example, in Fig. 4, switch 1 is presented in its on position with a contactor 11 held against the "points 12-12 (of which one is shown-in the figure) by a spring :13. This is the positionof this switch as diagrammedin Fig. 7. When the button 14 of switch 1, in the position of Fig. 4, is
depressed, cits contactor 11 moves on? and awayfrom the points 12-12 to'its dotted or off position. This p0sition is'diagrammed inFig.8.
the pivot axis than the other.
The contactor 11 then remains in this position, even after the depressing force is removed from the button, permitting a spring (not shown) to return the button to its normal position as shown diagrammatically in Fig. 9. However, when the button 14 of switch 1 is thereafter again depressed its contactor 11 once again moves over to the points to resume its on position as in Figs. 4 and 6, where it then remainsafter being released as in Fig. 7.
Switch 2, as detailed in Fig. 5,,is normally 01f and, in this position, a spring 15 holds the push button :14 up and the contactorll awayfrom the points 12-12. This is the position of this switch in Figs. 7 and 9.
When a downward force is applied tothe button 14 of this switch, and maintained on same, it overcomes the spring resistance and presses the contactor against the points to make its portion of the circuit. This condition is diagrammed in Figs. 6 and 8.
An opening 8 is provided for each switch so that, when installed in the wall 6 of the housing 7, the buttons 14-14 of both switches'arein aposition to be actuated approximately simultaneouslyby a'lever 10. This lever or pedal is pivotably connectedto the housing 7 by two pivot pins or screws 16-16 rctained in flanges 17-17 formed on the edges of the lever 10. Said pins or screws 16-16 pass into two clearance'holes 18-18 in thesides of the housing 7.
T he lever 10 coveringboth buttons is-obviously provided so that a single force and movement of one foot, hand or knee will, through it, move both buttons 14 at approximately the same time. After being depressed and held down momentarily it is automatically returned to its normal, upper position, as shown in Figs. 1, 2, and 3 by the buttons 14 actuated'by springs under the buttons such as the spring 15 in Fig. 5.
The openings 8-8 into which the switches are mounted may be elongated in-a direction at right angles to the axis of the pivot pins 16-16 or one opening S-may be placed a small distance 'inthis direction further from This asymmetry permits one switchto be'mounted further from the axis than the other. The buton 14 of one switch may also be raised higher than the button 14 of the other.
By these means the lever 10 can move the button of one switch through a greater distance than the other or cause one switch to make or break contact before the other.
'This may be necessary to accommodate for diiferent travel requirements of :the contactors or buttons of the two switches and to assure the electrical sequence desired.
T heswitches are wired into the power circuit with insulated electrical conductors 20-20 which pass through openings 21-21 in the switch housing 7.
The conductors 20-20 are then assembled toterminals of the switch points 12-12, and to the motor and power source, in the manner'indica'ted by the wiring 'dia gram of Figs. 6 through 7.
After assembling and wiring the switches inthe housing 7, the lever control or ped-al, 10 is attached by placing it in positiomlike a saddle, with the flanges 17 over the sides of the housing 7.
Tapped holes in the flanges are placed over clearance holes 18, in the housing, and pivot screws 16 are thereafter inserted into the tapped holes.
The housing 7 is provided with a hickey or extruded hook 22 designed to catch a turned up edge of a cover or closure member 23, which is then assembled to the housing by a screw 24.
Mode :0) operation On completing the assembly'described above switch 1 may be in the position of Fig. 7 or it may be in the position of Fig. *9. If in theposition of Fig. 9 it may be desirable to depress the pedal once and thereafter release it once, thereby putting it and the control in the safety position of Fig. 7 which is the position it will assume each time after having been used to actuate a power unit.
Reference can now be made to the two columns of the outline hereinabove of the sequence of operators motions and circuit effects thereof and to Figs. 6 through 9 in conjunction therewith:
Operators motion No. 1 changes the control from the position of Fig. 7 to that of Fig. 8. Although switch 2 thereby makes contact, switch 1 goes off. The net result is that the circuit remains open and no power is transmited.
Operators release, motion No. 2, thereafter results in the control assuming the normalposition of Fig. 9 with both switches off, the pedal 10 being raised by the spring of switch 2.
Operators second push, or motion No. 3, puts both switches on and the circuit now is closed to permit power transmission for as long as the control pedal is held down as indicated in Fig. 6.
Upon releasing the pedal, motion No. 4, the control surface then returns to the initial and normal position as indicated in Fig. 7 and, although switch 1 remains on, the circuit is broken by switch 2 thereby cutting off the power.
It is desirable that, with motion No. 1, switch 1 should go o a fractional moment before switch 2 goes on in order to prevent the possibility of the slightest surge of power. The button of switch 1 may therefore be raised slightly above that of switch 2 if both switches have the same travel to the point of making and breaking contact. If they do not have the same travel, or if, for example, switch 1 has a greater travel, it may also be positioned farther from the pivot axis of the control lever.
This adjustment will also generally cause switch 1 to go on just before switch 2 with the No. 3 motion or second push. However there is no objection to this effect. The capacity or a switch is usually limited by its resistance to deterioration from the are caused by the separation of the contacts on breaking the current fiow. This is always accomplished by switch l on motion 4. Therefore the capacity of this switch would determine the capacity of the combination.
It should be understood that numerous modifications may be made of the specific and preferred embodiment above described without deviating from the broader aspects of the invention.
'For example, a variety of known mechanisms can be arranged to supply, in a single switch body and with one set of contacts, the cycle of motions and circuit effects now provided so conveniently by two switches. As another example, a switch or switches with toggle or lever actuators or trigger bats may be employed with or without spring returns. A mechanical connection could be provided from the switch control to the control lever 10 with an external spring to return the control lever and the switch control members to the normal position. The control lever 10 could actually be omitted if the two switches were combined into one or if their control buttons were so close together that when depressed by the toe of a shoe they would move together.
(1) Depress control surface: circuit remains open; (2) Release control surface: circuit remains open; (3) Depress control surface: circuit closes;
(4) Release control surface: circuit opens,
thus avoiding accidental operation of a power tool after each operation thereof.
2. In combination, in a power tool controller, two electric switches wired in series on one side of a power circuit and arranged to be actuated approximately simultaneously; one of said switches being a push on, push off, type and the other being a momentary, normally off, type to produce the following, indefinitely repeating, sequence of actuation cause and circuit efiect:
(1) Press said switches: circuit remains open; (2) Release pressure: circuit remains open;
(3) Press said switches: circuit closes;
(4) Release said switches: circuit opens,
thus avoiding accidental operation of a power tool after each operation thereof.
3. In a power tool controller, a manually depressible, automatically returned, control surface actuating an electric switch, said switch comprising at least one set of two contact points and a contactor for each set of points, said points being wired in series on one side of an electric power circuit; means, coacting with said control surface to press said contactors against said points in the following indefinitely repeating sequence:
(1) Depress control surface: all but one of said contactors contact each set of poinnts;
(2) Release control surface: at least one of said contactors does not contact a set of points;
(3) Depress control surface: all contactors contact all sets of points;
(4) Release control surface: at least one of said contactors does not contact a set of points,
thus providing an on-off power cycle requiring a double motion of the controller operator to avoid accidental operation of a power tool after each operation thereof.
References Cited in the file of this patent UNITED STATES PATENTS 2,466,910 Pomerantz Apr. 12, 1949 2,482,540 Furnas Sept. 20, 1949 2,511,217 Mix June 13, 1950