Sealed variable resistor

Abstract: A sealed variable resistor (2) is made by enclosing a variable resistor and an arm member (6) attached to a shaft of the variable resistor in a sealing container (1), and rotatably supporting a dial knob (9) on a shaft outside the sealing container such that when the dial knob is energized, the arm member moves in association by virtue of magnetic force. The reliability and operability of such a sealed variable resistor are improved by forming the arm member and dial knob into a circular plate, and attaching to the arm member and dial knob at least two magnet pairs (8,10) separate from each other. These render the sealed variable resistor useful in various electrical devices which may be exposed to moisture when in use.

Description: This invention relates to a sealed variable resistor, in particular, to one for use in humid surroundings such as in bathrooms and bathtubs. In electrotherapeutic devices directed to use in such humid surroundings, it is an important issue to assure water-and moisture; proofing for variable resistors as output controllers and power switches in the devices. Although perfect water- and moistureproofing are attainable for oscillators and batteries by enclosing them in waterproofed sealing containers it is very difficult to waterproof perfectly certain elements with movable parts such as variable resistors and power switches. The inventor has previously devised a sealed variable resistor comprising enclosing a variable resistor and an arm member attached to a shaft of the variable resistor in a sealing container, and rotatably supporting a dial knob about a shaft outside the sealing container such that when said dial knob is energized, said arm member moves in association by virtue of magnetic force. This sealed variable resistor is disclosed in Japanese Utility Model Kokai No 40,953/88 and EP-A-262800. This sealed variable resistor however has the disadvantage that it is low in reliability because a decreased adhesive strength between the arm member and dial knob results in undesirable slippage and backlash. The device does have the advantage that it easily realizes the prescribed water- and moistureproofing and also has a smooth operation. An attempt to improve the adhesive strength using stronger magnets however has proved unsuccessful because this tends to cause a contrary effect, i.e. damaging the balance between the arm member and dial knob and leading to a low operability of the dial knob. One object of embodiments of this invention is to provide a sealed variable resistor which is free from the disadvantage of the prior art and attains a superior, high reliability, operability and impact resistance even when relatively weak or small magnets are used. The inventor particularly studied the shape of arm members and dial knobs, as well as studying the arrangement of magnets. As the result, in a sealed variable resistor which comprises enclosing a variable resistor and an arm member attached to a shaft of the variable resistor in a sealing container, and rotatably supporting a dial knob about a shaft outside the sealing container such that when the dial knob is energized, the arm member moves in association by virtue of magnetic force, the inventor discovered that the object may be attained by forming the arm member and dial knob from a circular plate, and attaching to the arm member and dial knob at least two magnet pairs apart from each other. According to the present invention there is provided a sealed variable resistor comprising the features of Claim 1. As the arm member and dial knob are formed into a plate and at least two magnet pairs are attached thereto, the arm member and dial knob can strongly adhere each other even when relatively weak or small magnets are used. Furthermore, since at least two magnet pairs are attached apart from each other, one can operate the dial knob with a relatively small power. Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which : FIG.1 is a vertical cross-sectional view of an embodiment of this invention; FIG.2 is the plan view of the embodiment of FIG. 1 ; FIG.3 is the top plain view showing an arrangement wherein a magnet pair is attached to an arm member and a dial; FIG.4 is the top plan view showing another arrangement wherein two magnet pairs are attached to an arm member and a dial knob; FIG.5 is the top plan view showing still another arrangement wherein three magnet pairs are attached to an arm member and a dial knob; and FIG.6 is the electric circuit of an electrotherapeutic device using a sealed variable resistor embodying this invention. Throughout the accompanying drawings, reference numeral (1) designates sealing container; (2), variable resistor; (3), bracket; (4), the concave on a bracket; (5), the shaft of a variable resistor; (6), arm member; (7), shaft-connecting shaft; (8, 10), magnets; (9), dial knob ; (11), mounting hole; (12), guiding concave; (13), supporting shaft; (14), attaching member; (15), scale; (16), pin; symbol R, resistor; C, capacitor; Tr, transistor; T, transformer; P, active electrode; E, dispersive electrode; B, battery; and SW, power switch. Now referring to FIG.1, reference numeral (1) designates a sealing container with appropriate waterproofing, moisture proofing and impact resistance, which is usually made from a magnetically permeable material such as plastic, ceramic or rubber. Reference numeral (2) designates a variable resistor. Its shape, electric resistance and power capacity are suitably chosen to meet its use. Since the sealed variable resistor embodying this invention has high adhesive strength between an arm member and a dial knob, variable resistors with a switch are favorably feasible in embodiments of the invention. Reference numeral (3) designates a bracket which fixes the variable resistor (2) inside the sealing container (1). The bracket (3) is prepared by forming a concave (4) on a metal plate, for example, of aluminum, iron, brass or stainless steel, and flanging its opposite sides. The variable resistor (2) is attached through approximately the center of the concave (4) such that a shaft (5) of the variable resistor (2) projects into the concave (4). The flanged parts of the bracket (3) are screwed onto the inside wall of the sealing container (1). Reference numeral (6) designates an arm member, which is usually prepared by forming a magnetically permeable material such as plastic, ceramics or rubber into a circular plate such as true circular, elliptic or polygonal form. Approximately at the center of the lower side of the arm member (6) is disposed a shaft-connecting shaft (7) in which one end of the shaft (5) is tightly inserted. Magnets (8) (10) in tablet form are disposed on the arm member (6) and dial knob (9) concentrically about the connecting shaft (7) to make an angle of about 180°, preferably, in the range of about 170° to about 179°, more preferably, in the range of about 173° to about 175°. The dial knob (9) is usually prepared by forming a magnetically permeable material such as plastic, ceramic and rubber into a circular plate such as true circular, elliptic or polygonal form. At the center of its lower side, it is provided with a mounting hole (11) with an engaging part such as roulette. The magnets (10) in tablet form are disposed on a circular line with an appropriate radius relative to the mounting hole (11). On the upper side of the dial knob (9) there is provided a guiding concave (12) which helps users smoothly operate the dial knob (9). The guiding concave (12) is replaceable with a handle of an appropriate shape. Reference numeral (13) designates a supporting shaft, which is made with a metal rod usually of brass or stainless steel. The top end of the supporting shaft (13) is flanged, while a roulette which fits in the mounting hole (11) is cut on the bottom end of the supporting shaft (13). Reference numeral (14) designates an attaching member for the supporting shaft (13). The attaching member (14) is made with a metal piece, through which the supporting shaft (13) is rotatably fixed onto the upper external wall of the sealing container (1) while covering the flanged part of the supporting shaft (13). The attaching member (14) per se is usually made of a stainless metal such as stainless steel, and screwed onto the upper external wall of the sealing container (1). The operation of the dial knob (9) becomes much smoother with an arrangement wherein a concentrical groove is concentrically provided about the mounting hole (11) on the lower side of the dial knob (9) while a corresponding boss is provided on the upper external wall of the sealing container (1), or with another arrangement wherein an appropriate bearing is disposed between the dial knob (9) and the upper external wall of the sealing container (1). If necessary, a scale (15) can be conveniently provided on an appropriate part of either the dial knob (9) or the upper external wall of the sealing container (1) as shown in FIG.2. This is very helpful to read the electric resistance of the variable resistor (1) and/or the ON/OFF position of switch, if any. The following experiments were carried out in order to establish the merits of disposing a plurality of magnet pairs (8)(10) according to embodiments of the invention. FIG.3 shows one arrangement (referred to as "Magnet 1" hereinafter) wherein one pair of magnets (8)(10) in tablet form are attached on an arm member (6) and a dial knob (9); FIG.4, another arrangement (referred to as "Magnet 2" hereinafter) wherein two pairs of magnets (8)(10) of the same shape and size are attached on an arm member (6) and a dial knob (9) of the same shape, size and material to make an angle of about 180° concentrically about a mounting hole (11); and FIG.5, still another arrangement (referred to as "Magnet 3" hereinafter) wherein three pairs of magnets (8)(10) of the same shape and size are attached on an arm member (6) and a dial (9) of the same shape, size and material to make an angle of about 120° concentrically about a mounting hole (11). Each arrangement was tested for its maximum adhesive strength, slippage on starting and during operation as a criterion of reliability, and backlash as a criterion of operability. Each arrangement was further tested for its connecting strength as a criterion of impact resistance. These characteristics were determined by the following methods: (i) Maximum adhesive strength As shown in FIGs.3-5, a pin (16) was concentrically set on the upper side of the dial knob (9). The pin (16) was applied with a mechanical force through a spring balance while keeping the arm member (6) immovable. Under these conditions, the force (gf) to put apart the magnets (8)(10) was determined. (ii) Slippage on starting Slippage (°) was determined with the circumferential scale by slowly moving the dial knob (9) till the arm member (6) started to move. (iii) Slippage during rotation Slippage (°) of the arm member (6) was determined when the dial knob (9) is turned by about 120°. (iv) Connecting strength Impact was applied to the pin (16) through a compressed spring balance while keeping the arm member (6) immovable. Under these conditions, the magnitude (gf) of the impact to disconnect the magnets (8)(10) was determined. These three arrangements were evaluated by grading the obtained scores into three ranks, i.e. "superior", "passable" and "inferior". The results were as shown in Table. Magnet 1 Magnet 2 Magnet 3 Maximum adhesive strength 116 gf 197 gf 403 gf Evaluation Inferior Passable Superior Slippage on starting 11.8° 2° 2° Evaluation Inferior Superior Superior Slippage during operation 10° 5° 3° Evaluation Inferior Passable Superior Backlash Inferior Superior Passable Connecting strength 178 gf 404 gf 598 gf Evaluation Inferior Superior Superior Judgement Control Embodiment of invention Embodiment of invention As evident from the results in Table, it was found that "Magnet 1" was poor in reliability because of low adhesive strength, large slippage on starting and during operation, and large backlash although it attained a relatively smooth operation. It was also found that "Magnet 2" was highest in reliability and least in slippage on starting and backlash because of reasonable structure and mechanical balance. Since "Magnet 3" was highest in adhesion strength, it was highly reliable and caused no substantial backlash and slippage even on starting and during operation. Since both "Magnet 2" and "Magnet 3" were higher in connecting strength, the magnets hardly disconnect even when applied with impact, and, if disconnected, are easily returnable to the normal arrangement. When all these data are put together, "Magnet 2", "Magnet 3" and "Magnet 1" can be graded in this order. It was also found that "Magnet 2" was far superior to "Magnet 3". As a consequence of the foregoing arrangement of embodiments of the invention, it can be favorably used in electrotherapeutic devices directed to use in bathrooms and bathtubs by enclosing, for example, a low-frequency oscillator and a battery, in the sealing container, and connecting through leads (not shown) the output of the oscillator with appropriate electrodes which are disposed outwardly the sealing container (1). FIG.6 shows the electric circuit of an electrotherapeutic device which is favorably feasible in such a use. Now explaining the operation of this circuit, a multivibrator comprising transistors Tr 1 and Tr 2 generates and supplies a square wave, for example, with a pulse width of about 0.1 second to about 10 seconds, pulse interval of about 0.1 second to about 10 seconds, to an emitter follower which comprises a transistor Tr 3 and has an appropriate time constant. Thus, a gradually increasing voltage is obtained. By supplying the voltage to the base of a transistor Tr 4 in a blocking oscillator which generates a diphasic action potential waveform, a diphasic action potential with a pulse interval varying a prescribed frequency is supplied across a pair of electrodes P and E because the oscillation frequency of such a blocking oscillator varies dependently on the magnitude of the base biasing voltage. The diphasic action potentials feasible with embodiments of this invention are those which have a frequency of about 1 hertz to about 200 hertz and a ratio of positive voltage component to negative voltage component in each of repeating pulsatile waves in the range of about 0.1:1 to about 0.5:1, preferably, in the range of about 0.2:1 to about 0.3:1, as well as having a duration for the negative voltage component in the range of about 0.001 second to about 0.01 second, preferably, about 0.002 seconds to about 0.005 seconds, and also a duration for the positive voltage component which lasts about 1.1 fold to about 2.0 folds, preferably, about 1.4 folds to about 1.6 folds of the duration for the negative voltage component. Comfortable electrotherapy free of side effects such as pain, redness, burn and unpleasantness is attainable by approximately equalizing the energies in forward and reverse directions in each of repeating pulsatile waves, or decreasing the energy in forward direction, preferably, by setting the ratio of the energy in forward direction to that in reverse direction in the range of about 0.1:1 to about 1:1, more preferably, in the range of about 0.2:1 to about 0.6:1. When in use, the power switch SW is first turned on, then the dispersive electrode E is put on a normal dermal site or placed in bathtub while turning down the variable resistor VR. Thereafter, the active electrode P is brought near to the affected site, and the variable resistor VR is gradually turned up to give a prescribed stimulation. Thus, the diphasic action potential is applied to the affected site. As described above, since in embodiments of this invention at least two magnet pairs are disposed on an arm member and a dial knob which are formed into circular plates, the arm member and dial knob exert a high adhesive strength and this decreases or even eliminates slippage during operation and backlash. Furthermore, since in embodiments of this invention at least two magnet pairs are attached apart from each other, the dial knob is smoothly operable even with a small power. Embodiments of this invention are therefore favorably usable for variable resistors for various electrical devices including electrotherapeutic devices which may be exposed to moisture.

Claims: A sealed variable resistor comprising: a variable resistor (2) with a shaft (5); a member (6) attached to the shaft (5) of said variable resistor (2); a sealing container (1) in which said variable resistor (2) and member (6) are enclosed; a dial knob (9) rotatably supported about a shaft (13) provided outside said sealing container (1) such that movement of said dial knob is coupled to said member (6) by virtue of magnetic force, characterised in that said member (6) and the dial knob (9) are both in the form of circular, elliptical or polygonal plates; that said plates confront each other across a wall of said sealing container (1); and that each of said member (6) and said dial knob (9) carry an equal plurality of spaced magnets (8, 10), whereby movement of said dial knob is coupled to said member (6). A sealed variable resistor as claimed in claim 1 wherein said plurality is two, and the magnets of one of said member (6) and said dial knob (9) are disposed symmetrically about the respective shaft, the magnets of the other of said member (6) and said dial knob (9) being disposed at an angle of 170-179 degrees to the respective shaft. A sealed variable resistor as claimed in claim 1 wherein said plurality is three or more, and the magnets on both said member (6) and said dial knob (9) are disposed regularly about the respective shaft.

Inventors: MASAKI KAZUMI, MASAKI, KAZUMI
Applicants: HAYASHIBARA KEN, HAYASHIBARA, KEN
Application year: 1990
Main classification: H01C10
IPC codes: H01C10, A63H17, A61N1, H01C1