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Publication numberUS2978084 A
Publication typeGrant
Publication dateApr 4, 1961
Filing dateOct 21, 1958
Priority dateOct 21, 1958
Publication numberUS 2978084 A, US 2978084A, US-A-2978084, US2978084 A, US2978084A
InventorsVilkaitis Hugo L
Original AssigneeSafeguard Mfg Company
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Safety interlock
US 2978084 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

April 1961 H. L. VILKAITIS 2,978,034

SAFETY INTERLOCK Filed Oct. 21, 1958 FIG. I

" INVENTOR.

3 HUGO L. V/L m4 lT/S I /6 a7 33 ATTORNEYS United States Patent SAFETY INTERLOCK Hugo L. Vilkaitis, Thomaston, Conn., assignor to Safeguard Manufacturing Company, Woodbury, Conn., a corporation of Connecticut Filed Oct. 21, 1958, Ser. No. 768,594

Claims. (Cl. 192-131) This invention relates to safety devices which control the operation of a machine and more particularly to a safety interlock requiring the presence of the operator or a portion of the operators body in a specific place before the machine can be operated.

It is an object of this invention to provide a safety interlock which is responsive to direct contact with the human skin to control the operation of a machine.

It is a further object of this invention to provide a reliable safety interlock that utilizes the operators body as part of an electrical circuit that controls the operation ofa machine and to do so in such a way as to avoid discomfort and possible injury to the operator by its use.

It is a still further object to provide a safety device which is inexpensive to manufacture, extremely reliable and foolproof in operation.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application of which will be indicated in the appended claims.

In the drawings:

Fig. l is a schematic side view of a press utilizing a preferred embodiment of this invention;

Fig. 2 is a perspective view of a pair of wristlets usable with the preferred embodiment;

Fig. 3 is a perspective view showing an alternate embodiment of a wristlet usable with this invention; and

Fig. 4 is a block diagram of an' electrical circuit usable with this invention.

Referring now to Fig. 1, it is seen that a punch press generally designated as 1 is provided with a poweroperated reciprocating slide 2 which engages a workpiece (not shown) on table 3 when the operator depresses treadle 4 to actuate the drive mechanism. Support pedestal 5 is mounted in front of press 1 and is provided with inwardly extending arm 6 which pivotally supports lever 7 at point 8. Lever 7 is pivotally connected to slide 2 by link 9 at one end and is secured to steel cables 10 and 11 at its other end so that depression of slide 2 pivots member 7 upwardly to draw cables 10 and 11 away from the punch press. Under normal conditions, wristlets 12 and 13 are secured to cables 10 and 11 and are firmly strapped on the wrist of the operator so that depression of treadle 4' operates slide 2 to forcibly withdraw the hands of the operator from the work area in the event that the operator himself fails to do so.

This safety system suffers from the difiiculty that the operator can merely fail" to wear the wristlets, thereby defeating the safety features of the machine while subjecting himself to possible serious injury. To prevent such unsafe operation of the machine and in accordance with the teachings of this invention, applicant provides a safety interlock which prevents operation of punch press ICC 1 unless wristlets 12 and 13 are properly worn by the operator.

Referring now to Figs. 1 and 2, it is seen that wristlet 12 is provided with an electrode 15 on its inner face so that when the wristlet is strapped in place electrode 15 engages the normally moist skin of the operator. Cable 10 is attached to wristlet 12 and carries therewith conductor 16 which leads to an external circuit subsequently described. Wristlet 13 is similar to wristlet 12 and is provided with an electrode 17 which is connected to an external circuit by conductor 18 which can be carried by cable 11. As most clearly seen in Fig. 2, wristlets 12 and 13 are bands of leather which adjustably engage the operators wrist through the action of buckle fasteners 19. As hereafter described more fully, electrodes 15 and 17 are made from dissimilar metals.

Referring now to Fig. 3, it is seen that an alternative embodiment of applicants invention utilizes a single wristlet in which two electrodes 20 and 21 are carried by the adjustable leather band or wristlet 22. Connection to the external circuit is established by conductors 23 and 24 and attachment to a safety cable 25 can be established by eyelet 26 fastened to the wristlet.

Referring now to the drawings in general and particularly Figs. 1 and 4, it is seen that electrodes 15 and 17 are connected to amplifier 30 through wires 16 and 18. It has been found that it is not necessary, however, to utilize separate conductors since the steel pull on cables can be used to transmit the signal. Amplifier 30 is of any common type, the only requirement being that it be capable of sensing the potential between elec trodes 15 and 17 and producing an output responsive to this potential which is of a sufiicient amplitude to operate a safety device. Amplifier 30 is energized from a suitable power source 31 through amplifier power sup ply connections 32 and 33. The output of amplifier 30 is connected to safety device 35 through connections'36 and 37. As most clearly seen in Fig. 1, the safety device generally designated as 35 in Fig. 4 is a solenoid 38. Solenoid 38, when energized, withdraws locking pin 40 from notch 41 in operating bar 42 thereby releasing treadle 4 for movement to operate punch press 1.

In operation, electrodes 15 and 17, when strapped on the wrists of the operator, establish a low potential between them because of the electrolytic action experienced when dissimilar metal electrodes are placed in contact with an electrolyte. The saline nature of moisture normally present on the surface of human skin acts as the necessary electrolyte in this invention. This potential difference will produce a minute current in the input of amplifier 30 which is amplified to actuate the safety device 35 (relay 38 in Fig. 1). The selection of metal for electrodes 15 and 17 can be made from the Table of Electrode Potential Series as set forth in International Critical Tables, volume 6, McGraw Hill Book Company, 1929. Any two metals from this series will exhibit a potential difference between them when in contact with an electrolyte. It has been found, however, that zinc and silver provide the best operating electrodes since they are reasonably inexpensive, not subject to excessive body action corrosion and produce a substantial potential difference by comparison between them. It has also been found that additional metals such as aluminum, gold and rhodium can be utilized with reasonable success.

Fig. 3 illustrates a wristlet containing two electrodes thereby permitting one-hand closure of the interlock circuit to control the operation of a machine. Fig. 3 also most clearly illustrates the use of mesh as the electrode. It has been found that the use of a mesh electrode not only permits intimate contact with the skin, but also can be used to greatly improve the mechanical strength of the 3 wristlet as, for example, by fastening the pull out cable 25 to the mesh.

It is therefore seen that this invention provides a reliable safety interlock that is sensitive to contact with human skin and that is ideally suited for use in a great many safety applications where reliability, comfort to the user, and size are of great importance.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above describedwill become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.

l lai 1. A safety device for power operated machines comprising a plurality of dissimilar metal electrodes, means for positioning said electrodes in contact with the normally moist skin of the machine operator thereby to establish an electrolytic potential between the electrodes, means electrically connected to said electrodes for amplifying the electrolytic potential established therebetween,

and means for controlling the operation of the machine, said last named means being operable by the output of said amplifier thereby to permit machine operation only when said dissimilar metal electrodes are in engagement with the skin of the operator.

2. A safety device for power operated machines comprising a plurality of dissimilar metal electrodes, a wristlet for positioning said electrodes in contact with the normally moist skin of the machine operator thereby to establish an electrolytic potential between the electrodes, means electrically connected to said electrodes for amplifying the electrolytic potential established therebetween,

and means for controlling the operation of the machine, said last named means being operable by the output of said amplifier thereby to permit machine operation only when said dissimilar metal electrodes are in engagement with the skin of the operator.

4 3. A safety interlock for presses and the like having a pair of wristlets that are, cable actuated by the press to withdraw the hands of the operator from the press operating area, said interlock comprising a first electrode positioned in one of the wristlets and engageable with the skin of the operatona second electrode positioned in the other of the wristlets and engageable with the skin of the operator, said first and second electrodes being made of dissimilar metals, an amplifier having input terminals connected to saidelectrodes thereby to amplify the electrolytic potential produced by contact of the electrodes with the normally moist skin of the operator, :1 safety device operable to permit press operation and means connecting the output of said amplifier to said safety device thereby to prevent operation of the press unless the electrodes carried by the wristlets are in engagement with the skin of the operator.

4. A safety device as set forth in claim 1 wherein each of said electrodes is made from a flexible metal mesh.

5. The safety device as set forth in claim 1 wherein said plurality of dissimilar metal electrodes includes at least one electrode made of zinc and a second electrode made of silver.

References Cited in the file of this patent UNITED STATES PATENTS 371,553 France Jan. 26,

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US505561 *Apr 19, 1892Sep 26, 1893 Electrical connection
US1889271 *Apr 22, 1931Nov 29, 1932Zerne Gustav AElectrical contact pad
US2013441 *Oct 12, 1934Sep 3, 1935Brown Joseph WSafety device for power presses
US2815749 *Nov 30, 1953Dec 10, 1957Nathan H FriedmanElectrocardiographic contact attachment
FR371553A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3047116 *Aug 27, 1958Jul 31, 1962Rockwell Standard CoSafety device for power presses
US3289671 *Sep 11, 1963Dec 6, 1966Glenn Troutman EdwinIontophoresis method
US3522868 *Jan 31, 1969Aug 4, 1970Bretford Mfg IncSupplemental safety device for press
US4566457 *Jul 24, 1985Jan 28, 1986Gunter StempleDefibrillator circuit and electrodes therefor
US4965909 *May 19, 1989Oct 30, 1990Mccullough Timothy JSafety control for power operated equipment
US5198702 *Feb 19, 1991Mar 30, 1993Mccullough Timothy JControl and safety system for electrically operated devices
US5272946 *Mar 20, 1992Dec 28, 1993Food Industry Equipment International, Inc.Safety control system for power operated equipment
US5510685 *Jul 22, 1994Apr 23, 1996Grasselli; GiorgioElectric motor control based on conductive contact of machine component with operator for injury prevention
US6813983Jan 16, 2002Nov 9, 2004Sd3, LlcPower saw with improved safety system
US6826988Jan 16, 2002Dec 7, 2004Sd3, LlcMiter saw with improved safety system
US6880440Jan 16, 2002Apr 19, 2005Sd3, LlcMiter saw with improved safety system
US6945148Jan 14, 2002Sep 20, 2005Sd3, LlcMiter saw with improved safety system
US6957601 *Sep 17, 2001Oct 25, 2005Sd3, LlcTranslation stop for use in power equipment
US6994004Jan 16, 2002Feb 7, 2006Sd3, LlcTable saw with improved safety system
US7000514Jul 25, 2002Feb 21, 2006Sd3, LlcSafety systems for band saws
US7077039Nov 12, 2002Jul 18, 2006Sd3, LlcDetection system for power equipment
US7197969Sep 13, 2002Apr 3, 2007Sd3, LlcLogic control with test mode for fast-acting safety system
US7231856Jun 13, 2002Jun 19, 2007Sd3, LlcApparatus and method for detecting dangerous conditions in power equipment
US7377199Jan 16, 2002May 27, 2008Sd3, LlcContact detection system for power equipment
US7481140Apr 15, 2005Jan 27, 2009Sd3, LlcDetection systems for power equipment
US7610836Nov 3, 2009Sd3, LlcReplaceable brake mechanism for power equipment
US7681479Mar 23, 2010Sd3, LlcMotion detecting system for use in a safety system for power equipment
US7707920Dec 31, 2004May 4, 2010Sd3, LlcTable saws with safety systems
US7712403Jul 2, 2002May 11, 2010Sd3, LlcActuators for use in fast-acting safety systems
US7784507Aug 19, 2005Aug 31, 2010Sd3, LlcRouter with improved safety system
US7788999Apr 10, 2006Sep 7, 2010Sd3, LlcBrake mechanism for power equipment
US7827890Nov 9, 2010Sd3, LlcTable saws with safety systems and systems to mount and index attachments
US7827893Mar 14, 2007Nov 9, 2010Sd3, LlcElevation mechanism for table saws
US7832314Nov 16, 2010Sd3, LlcBrake positioning system
US7836804Dec 29, 2006Nov 23, 2010Sd3, LlcWoodworking machines with overmolded arbors
US7866239Mar 14, 2007Jan 11, 2011Sd3, LlcElevation mechanism for table saws
US7895927May 19, 2010Mar 1, 2011Sd3, LlcPower equipment with detection and reaction systems
US7921754Apr 12, 2011Sd3, LlcLogic control for fast-acting safety system
US7991503May 18, 2009Aug 2, 2011Sd3, LlcDetection systems for power equipment
US8061245Nov 22, 2011Sd3, LlcSafety methods for use in power equipment
US8065943Nov 29, 2011Sd3, LlcTranslation stop for use in power equipment
US8087438Jan 3, 2012Sd3, LlcDetection systems for power equipment
US8100039Apr 19, 2010Jan 24, 2012Sd3, LlcMiter saw with safety system
US8122807May 3, 2010Feb 28, 2012Sd3, LlcTable saws with safety systems
US8151675Mar 31, 2011Apr 10, 2012Sd3, LlcLogic control for fast-acting safety system
US8186255Nov 16, 2009May 29, 2012Sd3, LlcContact detection system for power equipment
US8191450Aug 20, 2010Jun 5, 2012Sd3, LlcPower equipment with detection and reaction systems
US8196499Aug 20, 2010Jun 12, 2012Sd3, LlcPower equipment with detection and reaction systems
US8408106Apr 2, 2013Sd3, LlcMethod of operating power equipment with detection and reaction systems
US8459157Jun 11, 2013Sd3, LlcBrake cartridges and mounting systems for brake cartridges
US8489223Dec 23, 2011Jul 16, 2013Sd3, LlcDetection systems for power equipment
US8498732Dec 19, 2011Jul 30, 2013Sd3, LlcDetection systems for power equipment
US8505424Nov 8, 2010Aug 13, 2013Sd3, LlcTable saws with safety systems and systems to mount and index attachments
US8522655Apr 9, 2012Sep 3, 2013Sd3, LlcLogic control for fast-acting safety system
US9038515Aug 29, 2013May 26, 2015Sd3, LlcLogic control for fast-acting safety system
US9044760 *Jul 27, 2011Jun 2, 2015Jeff BuchananWearable safety device for cutting machine
US20020017176 *Aug 13, 2001Feb 14, 2002Gass Stephen F.Detection system for power equipment
US20020017336 *Aug 13, 2001Feb 14, 2002Gass Stephen F.Apparatus and method for detecting dangerous conditions in power equipment
US20020020265 *Sep 17, 2001Feb 21, 2002Gass Stephen F.Translation stop for use in power equipment
US20020059854 *Jan 16, 2002May 23, 2002Gass Stephen F.Miter saw with improved safety system
US20020069734 *Jan 16, 2002Jun 13, 2002Gass Stephen F.Contact detection system for power equipment
US20020190581 *Jun 13, 2002Dec 19, 2002Gass Stephen F.Apparatus and method for detecting dangerous conditions in power equipment
US20030002942 *Jul 2, 2002Jan 2, 2003Gass Stephen F.Discrete proximity detection system
US20030005588 *Jul 2, 2002Jan 9, 2003Gass Stephen F.Actuators for use in fast-acting safety systems
US20030020336 *Jul 25, 2002Jan 30, 2003Gass Stephen F.Actuators for use in fast-acting safety systems
US20030115804 *Mar 14, 2001Jun 26, 2003Goran SundolmFire door and a fire protection system
US20070240786 *Jun 4, 2007Oct 18, 2007Gass Stephen FMotion detecting system for use in a safety system for power equipment
US20120152072 *Jul 27, 2011Jun 21, 2012Jeff BuchananWearable safety device for cutting machine
EP0362937A2 *Sep 28, 1989Apr 11, 1990Giorgio GrasselliSafety control system for power operated equipment
WO1991013285A1 *Feb 20, 1991Sep 5, 1991Barbagli AndreIndustrial protection and safety system
WO2015025069A1 *Aug 12, 2014Feb 26, 2015Sanchez Jose Maria MartinezDevice for preventing work accidents
Classifications
U.S. Classification192/131.00R, 192/131.00H, 200/61.5, 200/61.58R
International ClassificationF16P3/00, F16P3/06
Cooperative ClassificationF16P3/06
European ClassificationF16P3/06