5,341,036
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`Aug. 23, 1994
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`USOO5341036A
`[11] Patent Number:
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`[45] Date of Patent:
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`_
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`Ulllted States Patent
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`Wheeler et al.
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`[19]
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`[54] TWO HAND OPERATED MACHINE
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`CONTROL STATION USING CAPACITIVE
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`PROXIMITY SWITCHES
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`Assistant Examz'ner—Fritz M. Fleming
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`Attorney, Agent, or Firm-—Larry I. Golden; D. Russell
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`Stacey; Larry T. Shrout
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`[75]
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`Inventors: Keith D. Wheeler; Stanley H.
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`Edwards’ Jr" both of Raleigh’ N'C'
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`Square D Company, Palatine, 111-
`[73] Assignee:
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`[21] Appl. No; 805,422
`_
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`{Z2}
`F’-led‘
`Dec‘ 11’ 1991
`[51]
`Int. C1.5 ............................................. .. H01H 9/26
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`[52] U.S. Cl. .................................... 307/328; 361/179;
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`361/189; 340/573; 192/131 R; 192/129 A
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`[58] Field of Search .............................. .. 307/ 1 16-1 1 8,
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`307/308, 326, 328, 140, 141.4; 361/ 179-18 1,
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`139, 230; 200/500, 51-35; 340/551. 552, 551,
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`563, 573; 323/5, 7, 1; 192/129 R-132 R
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`References Cited
`Us‘ PATENT DOCUMENTS
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`5/1963 Camfield et al.
`................... 361/189
`3,089,985
`
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`2/1971 Weidenfeld
`3,560,800
`307/115
`3,7s4,s191o/1973 Muller
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`361/189
`7/1975 Geremia ..
`3,895,269
`
`
`307/116
`6/1977 H012 ......H
`4,031,408
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`
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`361/139 X
`4,074,602 2/1973 Brower
`
`
`351/181
`4,412,268 10/1983 Dassow
`
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`307/116
`4,767,940
`8/1988 Turtle ......
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`307/139
`5,168,173 12/1992 Windsor ..
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`
`5/1993 Panter ............................... .. 361/181
`5,212,621
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`
`Primary Examiner-—A. D. Pellinen
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`ABSTRACI‘
`[57]
`A machine operator control station circuit which uses
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`capacitive proximity switches to replicate the function
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`of mechanical switches used in prior art control sta-
`tions. A monitoring circuit for monitoring the “on”
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`state of the capacitive proximity switches used in a two
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`hand industrial machine control Station is disclosed The
`circuit also reduces the chance of unintended operation
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`of the machine being controlled as a result of emitted or
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`conducted radio frequency interference which might be
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`detected by the capacitive proximity switches. An isola-
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`tion transformer provides an isolated power supply for
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`the monitoring circuit. The monitoring circuit includes
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`a first capacitive proximity switch for, detecting the
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`presence of one of the machine operator s ha.nds, and a
`second capacitive proximity switch for detecting the
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`presence of the other of the machine operator’s hands.
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`Each proximity Switch has a monitoring circuit for
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`m°“‘t°mg the length °f “me the p’°xmmy swmh
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`remains in the activated or “on” state. The monitoring
`circuits Of the first and second proximity switches are
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`connected together such that both switches must be
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`activated within a set time window in order to activate
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`the machine Conn-01 circuit
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`10 Claims, 6 Drawing Sheets
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`USTRIALMACHINE
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`SAMSUNG EXHIBIT 1015
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`U.S. Patent
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`Aug. 23, 1994
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`Sheet 1 of 6
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`(5153526)
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`4
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`I NDUSTRIAL
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`MACHINE
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`U.S. Patent
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`Aug. 23, 1994
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`Sheet 2 of 6
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`5,341,036
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`L1 L2
`O
`C
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`DC
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`POWER SUPPLY
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`85
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`INDUSTRIAL
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`U.S. Patent
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`.m3aehS
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`6
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`5,341,036
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`A!§,ms8EIv
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`\\\o\m_\\\\\\tm_\mN_
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`m.o_.._
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`U.S. Patent
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`Aug. 23, 1994
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`Sheet 4 of 6
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`U.S. Patent
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`Aug. 23, 1994
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`Sheet 5 of 6
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`/ V /
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`<— FREQUENCY (KHz)——-
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`FlG.6
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`U.S. Patent
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`Aug. 23, 1994
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`Sheet 6 of 6
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`5,341,036
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`Page 7 of 13
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`25
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`1
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`TWO HAND OPERATED MACHINE CONTROL
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`STATION USING CAPACITIVE PROXIMITY
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`SWITCHES
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`FIELD OF THE INVENTION
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`The present invention relates to industrial machine
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`controls which require two hand operation to meet
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`O.S.H.A. standards, and particularly to industrial ma-
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`chine controls using capacitive proximity switches as a
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`means for the machine operator to activate the machine.
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`BACKGROUND OF THE INVENTION
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`O.S.H.A. requirements for many industrial machine
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`controls specify that the operator must use both hands
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`to initiate operation of the machine. This requirement
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`was established to prevent possible hand injuries to the
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`machine operator. Most machine control stations of this
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`type employ two palm button mechanical switches. The
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`two palm buttons must close the operating circuit to
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`cause the machine to operate. The force required to
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`press the palm buttons is variable with each palm but-
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`ton, however, it is sufficient enough to give the operator
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`a “tactile fee ” indicating to him that the switch has
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`been activated. U.S. Pat. No. 4,412,268 to Dessow dis-
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`closes an industrial machine control station employing
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`two proximity switches which replicate the function of
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`the more
`conventional palm button mechanical
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`switches for controlling an industrial machine. In Das-
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`sow’s device the machine operator is required to touch
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`a sensing plate to operate the machine. The control
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`circuit of Dessow does not provide for proximity
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`switch failure monitoring. It is also noted that the ma-
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`chine control station disclosed in the patent to Dassow
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`has output contacts which are connected in series with
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`the line power to the machine being controlled. As a
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`result, the high current carried by the output contacts
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`significantly increases the chance of welding such
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`contacts closed which could result in the machine being
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`controlled continuing to run after the operator has re-
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`moved his hands from the operator station. Dassow’s
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`output circuit is also controlled by an anti-cheat timer
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`which would appear to provide a pulsed output to the
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`machine. A pulsed output would require adjustment to
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`match the machine’s operating time cycle. The patent to
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`Dassow also discloses the provision of proximity
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`switches which are tuned to different frequencies for
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`the purpose of preventing “inadvertent operation as a
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`consequence of operating the first switch”,
`i.e. unin-
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`tended activation of one of the two proximity switches
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`caused by interference from the other switch. However,
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`the patent to Dassow does not address or even recog-
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`nize the problem of unintended simultaneous activation
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`of both capacitive proximity switches which is caused
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`by the presence of emitted or conducted radio fre-
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`quency interference.
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`SUMMARY OF THE INVENTION
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`A first object of the present invention is to provide a
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`more ergonomic operator station by eliminating the
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`physical contact pressure required to activate prior art
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`machine controls of the type using two palm button
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`switches. This is achieved by incorporating two capaci-
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`tive proximity switches, spaced apart one from the
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`other at a distance comfortable for the machine opera-
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`tor, and mounted in a machine control station. The
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`capacitive proximity switches do not require physical
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`contact by the machine operator to be activated or
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`5,341,036
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`2
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`turned “on”. To activate the capacitive proximity
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`switch the machine operator places his hand in the
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`sensing field of the switch. Therefore,
`the machine
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`operator is not subjected to the repetitive pressing of
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`palm button switches required with prior art devices.
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`Since there is no physical pressure required to acti-
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`vate a capacitive proximity switch, the machine opera-
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`tor will have no tactile feedback to indicate that the
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`switch has been activated. Accordingly, a second ob-
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`ject of the present invention is to provide an indicator
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`light source in the capacitive proximity switch circuit
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`for providing the machine operator with a visual indica-
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`tion that the capacitive proximity switch has been acti-
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`vated. In the preferred embodiment of the present in-
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`vention, this indicator light is placed at a point in the
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`machine control station that is easily visible to the ma-
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`chine operator.
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`A third object of the present invention is to provide a
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`capacitive proximity switch monitoring circuit which
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`will prevent the machine control station of the present
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`invention from operating ‘the machine to which it is
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`connected if either capacitive proximity switch should
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`fail in the “on” state, or have an object placed in its
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`sensing field for an extended period of time. In the
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`preferred embodiment of the present invention, a moni-
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`toring circuit is provided for each of the two capacitive
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`proximity switches. Each monitoring circuit includes an
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`interval timer relay which monitors the length of time
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`the capacitive proximity switch is in the “on” state. The
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`interval timer relay has a normally open contact which
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`controls an output control relay. The output control
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`relay provides normally open and normally closed
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`contacts to the input circuit of the machine control. If
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`the capacitive proximity switch is “on” for a period of
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`time longer than the interval timer relay is programmed
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`for, its normally open contact will open. This in turn
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`will deenergize the output control relay causing its
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`normally open contact to open and thereby open the
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`output circuit of the machine control station. The nor-
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`mally open contact of the interval timer relay will re-
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`main open until the interval timer relay has been reset.
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`The interval timer relay can only be reset when the
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`capacitive proximity switch is returned to the “off”
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`state or a failed “on” switch has been replaced with a
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`new capacitive proximity switch. Therefore, if someone
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`places an object in the proximity sensing field or the
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`capacitive proximity switch should fail in the “on” state
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`the interval timer relay normally open contacts will
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`open causing the output control relay to deenergize and
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`therefore open the machine control output circuit pro-
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`hibiting machine operation.
`Each of the sensor monitoring circuits are electrically
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`coupled together such that the machine operator must
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`activate both capacitive proximity switches within a
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`specific time window in order to initiate the machine
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`operation. This time window is determined by the first
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`interval timer relay to be activated. If both capacitive
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`proximity switches are not activated within this time
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`window they must both be returned to the “off” state to
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`reset their respective interval timer relays. If both inter-
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`val timer relays are not reset the machine control output
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`circuit cannot be activated.
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`A fourth object of the machine control station of the
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`present invention is to provide an isolated output from
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`the machine control station to the machine such that
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`any voltage required to operate the machine may be
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`controlled by the operator at the machine control sta-
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`5,341,036
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`tion. This is accomplished by providing isolated nor-
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`mally closed and normally open output terminals associ-
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`ated with each capacitive proximity switch for the con-
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`trol power to the machine being operated. The isolated
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`outputs also permit this machine control circuit to be
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`retrofitted to machines having O.S.I-I.A. approved anti-
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`tie down and anti-repeat circuits.
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`A fifth object of the machine control station of the
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`present invention is to provide a continuous, non—pu1sed
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`output to the machine being controlled. This is accom-
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`plished by using a timer bypass relay to control the
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`isolated output contacts. The timer bypass relay is ener-
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`gized only when both capacitive proximity switches are
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`activated within the time window. The timer bypass
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`relay will remain energized as long as both capacitive
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`proximity switches remain activated.
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`A sixth object of the present invention is to provide a
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`machine control station employing capacitive proximity
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`ence from most conducted or emitted radio frequencies.
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`It has been determined that a capacitive proximity sen-
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`sor can be activated by conducted or emitted radio
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`frequencies that are at or near the internal oscillator
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`frequency of the sensor. Certain types and shapes of
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`enclosure enhance the detecting capabilities of capaci-
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`tive sensors and thereby increase the probability of
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`inadvertent activation by radiated radio frequency in-
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`terference. In the machine control station of the present
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`invention, the possibility of radiated radio frequency
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`interference activating both sensors simultaneously is
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`minimized by providing for the two capacitive proxim-
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`ity switches having internal operating frequencies
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`which are sufficiently separated as discussed in greater
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`detail in the detailed description of the preferred em-
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`bodiment hereinbelow. Capacitive proximity switches
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`may also be inadvertently activated by conducted radio
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`frequency interference. The possibility of simultaneous
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`activation of the two capacitive proximity switches by
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`conducted radio frequency interference is minimized in
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`the present invention by the provision of an isolation
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`transformer placed in its power input circuit. In either
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`case the status of the capacitive proximity switch is
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`displayed to the operator by the indicator lights pro-
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`vided by the present invention.
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`Other features and advantages of the invention will
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`become apparent to those skilled in the art upon review
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`of the following detailed description, claims and draw-
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`mgs.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 is a schematic of an AC cmpacitive proximity
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`switch monitoring and indicator light circuit for a ma-
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`chine operator control station constructed in accor-
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`dance with the present invention.
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`FIG. 2 is a schematic of a second embodiment of the
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`capacitive proximity switch monitoring circuit of a
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`machine operator control station constructed in accor-
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`dance with the present invention for use with DC cir-
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`cuits.
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`FIG. 3 is a graph of the relationship of the frequency
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`sensitivity curves of the two capacitive proximity
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`switches utilized by the present invention with respect
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`to a radio frequency field strength expressed in volts per
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`meter.
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`FIG. 4 is a cross-sectional view of a portion of a
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`machine operator control station constructed in accor-
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`dance with the present invention which is illustrative of
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`4
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`the relative positioning of the enclosure and sensing pad
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`embodied by the control station.
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`FIG. 5 is a graph of the relationship of the frequency
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`sensitivity with respect to the field strength, expressed
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`in volts per meter, of a capacitive proximity switch
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`having its sensing plate positioned in approximately the
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`same plane as the surface of the enclosure of a machine
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`operator control station constructed in accordance with
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`the present invention as compared to having the sensing
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`plate positioned above (outboard) the surface of the
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`enclosure or below (inboard) the surface of the enclo-
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`sure as it is positioned in the preferred embodiment of
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`the surface of the enclosure or below (inboard) the
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`surface of the present invention.
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`FIG. 6 is a graph of the relationship of the frequency
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`sensitivity with respect to the field strength, expressed
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`in volts per meter, of the two capacitive proximity
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`switches having their sensing plates positioned below
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`(inboard of) the plane of the surface of the enclosure, as
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`they are positioned in the preferred embodiment of a
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`machine operator control station constructed in accor-
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`dance with the present invention, as compared to hav-
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`ing their sensing plates positioned in approximately the
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`same plane as the surface of the enclosure.
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`FIG. 7 is an isometric view of an enclosure for a
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`machine operator control station constructed in accor-
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`dance with the present invention.
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`Before one embodiment of the invention is explained
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`in detail, it is to be understood that the invention is not
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`limited in its application to the details of construction
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`and description or illustrated in the drawings. The in-
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`vention is capable of other embodiments and of being
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`practiced or being carried out in various other ways.
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`Also, it is to be understood that the phraseology and
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`terminology used herein is for the purpose of descrip-
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`tion and should not be regarded as limiting.
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`DESCRIPTION OF THE PREFERRED
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`EMBODIMENT
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`An AC electrical circuit 10 for a two hand industrial
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`machine operator control station having capacitive
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`proximity switches which replicate the function of palm
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`button mechanical switches used in prior art control
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`stations is shown in FIG. 1. The circuit 10 is designed to
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`prevent an industrial machine 13 from operating if ei-
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`ther of the two capacitive proximity switches 14, 42
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`should fail in the “on” state, or if an object is placed in
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`the sensing field of either capacitive proximity switch
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`for an extended period of time. The circuit 10 is also
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`designed to reduce the chance of inadvertent simulta-
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`neous activation of the capacitive proximity switches 14
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`and 42 by an emitted or conducted radio frequency.
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`Referring to FIG. 1, the circuit 10 includes an isola-
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`tion transformer 12 having terminals L1 and L2 for
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`connecting to an external AC power source and a pri-
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`mary 12’ and secondary 12". The isolation transformer
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`12, through the secondary 12", provides an isolated AC
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`power supply to the circuit 10, a first AC 2-wire capaci-
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`tive proximity switch 14 which can be activated (closed
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`or placed in the “on” state) by the presence of one of the
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`machine operator’s hands within its sensing field, a
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`capacitive proximity switch monitor comprising a first
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`interval timer relay 18 having a normally open electri-
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`cal contact 22, a first output control relay 26 having a
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`first normally open electrical contact 30, a second nor-
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`mally open electrical contact 34 and a normally closed
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`electrical contact 36, a first indicator light source 38, a
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`second AC 2-wire capacitive proximity switch 42
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`Page 9 of 13
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`6
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`The second normally open contacts 34 and 62 of first
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`and second output control relays 26 and 54 respectively
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`are the isolated output terminals for connecting the
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`machine control station to the circuitry of the industrial
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`machine 13 to be operated. The normally closed
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`contacts 36 and 64 of first and second output control
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`relays 26 and 54, respectively, are isolated outputs for
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`connecting to an O.S.H.A. approved anti-tie down cir-
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`cuit.
`It will be apparent to those skilled in the art that if a
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`machine operator activates both capacitive proximity
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`switches 14 and 42 within the preselected time interval
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`determined by the first interval timer relay, 18 or 46, to
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`be activated, the first and second output control relays
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`26 and 54 respectively will be energized, closing the
`first normally open contacts 30 and 58 of the first and
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`second output control relays 26 and 54, respectively,
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`thereby energizing timer bypass relay 70. Energizing
`the timer bypass relay 70 closes its first and second
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`normally open contacts 74 and 78, respectively, thereby
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`keeping the first and second output control relays 26
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`and 54, respectively, energized when the contacts 22
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`and 50 open after the expiration of the time intervals
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`determined by the relays 18 and 46, respectively. There-
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`after, as long as both first and second capacitive proxim-
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`ity switches 14 and 42, respectively, are simultaneously
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`held in the “on” state,
`the second normally open
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`contacts 34 and 62 of first and second output control
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`relays 26 and 54 respectively will be closed and the
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`normally closed contacts 36 and 64 of first and second
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`output control relays 26 and 54 respectively will be
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`open permitting a non-pulsed control signal to be sent to
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`the industrial machine 13.
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`It will also be apparent to those skilled in the art that
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`if the machine operator does not activate both capaci-
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`tive proximity switches 14 and 42 within the time win-
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`dow defined by the first interval timer relay to be acti-
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`vated, the first interval timer to be energized will cause
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`its associated normally open contact 22 or 50 to open
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`thereby deenergizing the associated first or second out-
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`put control relay 26 or 54 respectively. This will in turn
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`cause the first and second normally open contacts and
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`the normally closed contact associated with the deener-
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`gized output control relay 26 or 54 to return to their
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`normal state, thereby preventing the industrial machine
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`from operating.
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`The interval timer relays 18 and 46 can only be reset
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`by deactivating or turning off their respective capaci-
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`tive proximity switches 14 and 42. It will be apparent to
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`those skilled in the art that if either of the interval timer
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`relays 18 or 46 is not reset after the relay 70 has been
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`deenergized, the associated output control relay 26 or
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`54, respectively, will remain deenergized while their
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`respective associated normally open isolated output
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`contacts 34 or 62 will not close nor will their respective
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`normally closed contacts 36 or 64 open, thus the ma-
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`chine 12 is prevented from operating.
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`It will be noted that in the preferred embodiment the
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`preselected time intervals during which contacts 22 and
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`50 remain closed after the interval timer relays 18 and
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`46, respectively, are energized are determined by the
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`selection and adjustment of the timer relays 18 and 46
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`and for most applications the intervals will be set to be
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`the same for both relays.
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`An alternate embodiment of the present invention for
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`use in DC circuits is shown in FIG. 2. The circuit 82
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`works in the essentially same manner as the AC moni-
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`toring circuit 10 of FIG. 1 and uses the many of the
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`5
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`which can be activated by the presence of the machine
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`operator’s other hand within its sensing field, a second
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`interval timer relay 46 having a normally open electri-
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`cal contact 50, a second output control relay 54 having
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`a first normally open electrical contact 58, a second
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`normally open electrical contact 62 and a normally
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`closed electrical contact 64, a second indicator light
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`source 66, and a timer bypass relay 70 having a first
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`normally open electrical contact 74 and a second nor-
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`mally open electrical contact 78.
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`Still referring to FIG. 1, the first capacitive proximity
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`switch 14 is connected in series with the first interval
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`timer relay 18 such that the relay 18 is energized when
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`the first capacitive proximity switch 14 is activated or
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`turned “on” by the presence of one of the machine
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`operator’s hands. The first interval timer relay 18 moni-
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`tors the length of time the first capacitive proximity
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`switch 14 is activated, or in the “on” state. When the
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`first interval timer relay 18 is energized, its normally
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`open contact 22, which is connected in series with and
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`between the first capacitive proximity switch 14 and the
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`first output control relay 26,
`is closed and remains
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`closed for a preselected interval of time; however,
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`contact 22 will immediately open if relay 18 becomes
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`deenergized. Closing contact 22 energizes the first out-
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`put control relay 26 which causes its first and second
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`normally open contacts 30 and 34, respectively, to close
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`and its normally closed contact 36 to open. The first
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`indicator light source 38, a neon light in the preferred
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`embodiment, is connected in series across the line with
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`the capacitive proximity switch 14 and is energized
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`when the first capacitive proximity switch 14 is acti-
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`vated and remains illuminated as long as the first capaci-
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`tive proximity switch I4 is in the “on” state.
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`Still referring to FIG. 1, the second capacitive prox-
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`imity switch 42 is connected in series with the second
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`interval timer relay 46 such that the second interval
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`timer relay 46 is activated when the second capacitive
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`proximity switch 42 is activated or turned “on” by the
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`presence of the other of the machine operator’s hands
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`within its sensing field. The second interval timer relay
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`46 monitors the length of time the second capacitive
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`proximity switch 42 is activated, or in the “on” state.
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`When the second interval timer relay 46 is activated its
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`normally open electrical contact 50, which is connected
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`in series with and between the second capacitive prox-
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`imity switch 42 and the second output control relay 54,
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`is closed and remains closed for a preselected interval of
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`time; however, contact 50‘ will immediately open if
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`relay 46 becomes deenergized. Closing contact 50 ener- 50
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`gizes the second output control relay 54, causing its first
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`and second normally open contacts 58 and 62, respec-
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`tively, to close and its normally closed contact 64 to
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`open. The second indicator light source 66, a neon light,
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`is also energized when the second capacitive proximity
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`switch 42 is activated and remains illuminated as long as
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`the second capacitive proximity switch 42 is in the “on”
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`state.
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`The first normally open contact 30 of the first output
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`control relay 26 and the first normally open contact 58
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`of the second output control relay 54 are connected in
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`series with the timer bypass relay 70. The first normally
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`open contact 74 of the timer bypass relay 70 is con-
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`nected in parallel with the normally open contact 22 of
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`the first interval timer relay 18 and the second normally 65
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`open contact 78 of the timer bypass relay 70 is con-
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`nected in parallel with the normally open contact 50 of
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`the second interval timer relay 46.
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`5,341,036
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`Page 10 of 13
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`5,341,036
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`7
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`same components described in the first embodiment
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`with the following exceptions. A DC power supply 86
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`provides DC power for the monitoring circuit 82. The
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`first AC 2-wire capacitive proximity switch 14 of the
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`previously described embodiment is replaced with a
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`first DC 3-wire capacitive proximity switch 90. The
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`first indicator light source 38 of the previously de-
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`scribed embodiment is replaced with a first indicator
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`light source 94, and in this embodiment is preferably a
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`light emitting diode (LED). The second AC 2-wire
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`capacitive proximity switch 42 of the previously de-
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`scribed embodiment is replaced with a second DC 3-
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`wire capacitive proximity switch 98. The second indica-
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