Anti-malfunction mechanism for variable output device

A variable output device is mounted on a mounting unit with the operating shaft displaceable. An operating unit for transmitting the operation of the user to the operating shaft is mounted on the operating shaft relatively movably along the direction of the axis of the operating shaft, on the one hand, and in an operatively interlocked fashion along the direction of displacement of the operating shaft, on the other hand. A holding member is arranged in opposed relation with the mounting unit with the variable output device interposed therebetween. An elasticity applier urges the operating unit away from the variable output device. The holding member is provided with an operating hole. The holding member is arranged at a position in opposed relation with the mounting unit with the variable output device and the operating unit interposed therebetween. The operating unit elastically urged by the elasticity applier is brought into contact with the peripheral edge portion of the operating hole of the holding member in opposed relation with the operating hole.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mechanism for preventing the malfunction of a variable output device built in various electronic apparatuses.

2. Description of the Related Art

Conventional electric apparatuses are available which comprise a variable output device such as a variable resistor and an operating unit therefor. The operating unit is a knob for manipulating and therefore adjusting the variable output device from outside the apparatus.

FIG. 10shows a mounting structure of a conventional operating unit5. A variable output device2is connected by solder to a circuit board1. The variable output device2has an operating shaft. The operating unit5is fitted on the operating shaft of the variable output device2to rotate integrally with the operating shaft. A part of the operating unit5is projected out of the electronic apparatus by way of a hole formed in an exterior case7of the electronic apparatus. The user adjusts the output of the variable output device2by rotating the operating unit5projected out of the apparatus. Various parameters of the electric apparatus are adjusted based on the output (amount of electricity, etc.) from the variable output device2. A single-unit video camera recorder, for example, uses this type of a variable output device for adjusting the voice level to be recorded.

The conventional mounting structure of the variable output device is not provided with a lock mechanism for preventing malfunction. Under an incidental external force or with an inadvertent operation of the operating unit5by the user, the operating unit5is undesirably rotated against the will of the user, with the inconvenient result that the parameters of the electric apparatus are unduly changed.

In a single-unit video camera recorder, for example, a malfunction of the operating unit of a variable output device for adjusting the voice level may change the voice level against the intention of the user during the recording operation.

SUMMARY OF THE INVENTION

Accordingly, the primary object of this invention is to prevent the movement of the operating unit against the will of the user.

In order to achieve this object, according to this invention, there is provided an anti-malfunction mechanism for a variable output device having an operating shaft adapted to be displaced under an external force, whereby the output is changed in accordance with the displacement of the operating shaft.

The anti-malfunction mechanism according to the invention comprises a mounting unit on which the variable output device is mounted, an operating unit operated by the user to transmit the resulting external force to the operating shaft, a holding member arranged in opposed relation to the mounting unit with the variable output unit therebetween, and an elasticity applier for elastically urging the operating unit.

The variable output device is mounted on the mounting unit with the operating shaft displaceable. The operating unit is mounted on the operating shaft relatively movably along the direction of the axis of the operating shaft, on the one hand, and in an operatively interlocked fashion along the direction of displacement of the operating shaft, on the other hand. The operating unit is elastically urged in the direction away from the variable output unit by the elasticity applier. The holding member is provided with an operating hole and arranged in opposed relation to the mounting unit with the variable output device and the operating unit therebetween. The operating unit elastically urged by the elasticity applier is brought into contact with the peripheral edge portion of the operating hole of the holding member in opposed relation to the operating hole.

As a result, according to this invention, as long as the operating unit is not pressed along the axial direction by the user, the operating unit is kept elastically urged into contact with the peripheral edge portion of the operating hole of the holding member. During this period, the operating unit is pressed fixedly against the holding member and therefore not substantially displaced. As a result, the malfunction of the electricity regulator in off state can be positively prevented.

According to this invention, a buffer member is preferably interposed between the operating unit and the peripheral edge portion of the operating hole of the holding member. By doing so, the operating unit is fixed on the holding member more securely and becomes more difficult to displace. Also, the buffer member enables the gap between the operating hole and the operating unit to be hermetically sealed.

According to this invention, the configuration described below is preferably employed. Specifically, an elasticity applier seat for supporting the elasticity applier is arranged on the operating shaft relatively movably in the direction along the axis of the operating shaft, on the one hand, and in an operatively interlocked manner in the direction of displacement of the operating shaft, on the other hand. The operating unit is mounted on the elasticity applier seat relatively movably in the axial direction and in operatively interlocked manner in the direction of displacement of the operating shaft. By doing so, the elastic force generated by the elasticity applier fails to reach the variable output device directly. As a result, the variable output device is not easily broken and the durability is not adversely affected.

The elasticity applier is, for example, a coil spring or a corrugated washer.

According to this invention, the elasticity applier seat is provided. This elasticity applier seat, when formed of a coil spring, preferably has a cylinder surrounding the elasticity applier. By doing so, the expansion/contraction of the elasticity applier is guided smoothly by the cylinder. Further, a taper for preventing the elasticity applier from being caught is preferably formed at the corner of the cylinder contacted by the elasticity applier. Then, the elasticity applier, when expanding or contracting, is not caught and operates more smoothly.

According to this invention, the configuration described below is preferably employed. Specifically, the variable output device includes a case with the operating shaft projected from an end thereof, and a protective member covering the end portion of the operating shaft on the case side. The elasticity applier seat is kept in contact with the protective member. By doing so, the end portion of the operating shaft on the case side is protected by the protective member. As a result, even in the case where the elastic force is applied repeatedly to the end portion of the operating shaft on the case side by the elasticity applier, the particular portion is not easily damaged and the reduction in the durability of the variable output device can be suppressed accordingly.

According to this invention, preferably, a metal sheet is provided on the surface of the operating unit contacted by the elasticity applier, and the elasticity applier is brought into contact with the metal sheet. By doing so, the functions and effects described below are obtained. Generally, the elasticity applier is configured of a metal, such as a steel, member from the viewpoint of the durability of the elastic force and cost. The operating unit, on the other hand, is often configured of a resin to reduce both cost and weight. After repeated elastic operations of the elasticity applier in contact with the operating unit, therefore, the operating unit is damaged and the durability thereof may be reduced. The provision of the metal sheet on the surface of the operating unit contacted by the elasticity applier can prevent the damage to the operating unit. In this case, the whole operating unit is not required to be configured of a metal, but only the portion thereof in contact with the elasticity applier is provided with a metal sheet. In this way, the increase of both cost and weight of the operating unit can be minimized. Incidentally, the metal sheet can be built in the operating unit of a resin by integral molding.

This invention is suitably applicable to a variable output device with the operating shaft thereof displaced in the direction of rotation.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the invention are described below with reference to the drawings.

First Embodiment

FIG. 1is a perspective view showing a general configuration of an electronic apparatus A having a built-in anti-malfunction mechanism for a variable output device according a first embodiment of the invention.FIG. 2is an exploded perspective view showing the structure of an anti-malfunction mechanism for a variable output device according to the first embodiment of the invention.FIG. 3is a sectional view showing the state in which a malfunction is prevented by the anti-malfunction mechanism for the variable output device according to the first embodiment.FIG. 4is a sectional view taken along line α—α in FIG.3.FIG. 5is a sectional view showing the state in which the anti-malfunction mechanism for the variable output device according to the first embodiment is in operation.

The electronic apparatus A according to this embodiment is a single-unit video camera recorder. The electronic apparatus A includes a variable output device2for adjusting the voice level at the time of video recording. The variable output device2is configured of, for embodiment, a variable resistor, a variable capacitor and a rotary encoder.

The anti-malfunction mechanism according to this embodiment is a mechanism for preventing the malfunction of the variable output device2built in the electronic apparatus A. The variable output device2is built in as a circuit part of the electronic apparatus A. The variable output device2is mounted on a circuit board1. The circuit board1is an embodiment of a mounting unit. In this embodiment the circuit board1is used as an example of a mounting unit. However, the mounting unit may be any other member on which the variable output device2can be mounted.

The circuit board1has mounted thereon various circuit parts including the variable output device2built in the electronic apparatus A. The variable output device2has an operating shaft2a. The operating shaft2ais rotated subject to a rotational operation by the user. The variable output device2produces an output (electrical resistance, capacitance, digital amount) changing in accordance with the rotational operation of the operating shaft2ato an external device. The operating shaft2ais projected outward of a case2bof the variable output device2. The operating shaft2ais projected along the direction perpendicular to the surface of the circuit board1. The operating shaft2ahas a flange2c. The flange2cis arranged in the vicinity of the surface of the case2b. Due to the presence of the flange2c, the operating shaft2aassumes a shape having a stepped portion on the surface of the case2b. The operating shaft2a, though cylindrical, is cut away in an arcuate form along the axis thereof and has a D-shaped cross section.

An elasticity applier seat3is fitted coaxially on the operating shaft2a. The elasticity applier seat3has an inner peripheral surface3ain the same shape (D-shaped cross section) as the operating shaft2a. The elasticity applier seat3, with the inner peripheral surface3athereof fitted on the outer peripheral surface of the operating shaft2a, is mounted on the operating shaft2ain a manner rotatable integrally therewith. An outer peripheral surface3bof the elasticity applier seat3is circumferential in shape. The outer peripheral surface3bis formed with keyways3c. The keyways3care formed along the axial direction on the outer peripheral surface3b. The elasticity applier seat3has a flange3d. The flange3dis arranged at an end of the elasticity applier seat3on the case2bside. The elasticity applier seat3is fitted on the operating shaft2awith the flange3dkept in contact with the flange2c.

A cylindrical operating unit5is coaxially fitted on the elasticity applier seat3. An inner peripheral surface5aof the operating unit5has the same shape as the outer peripheral surface of the elasticity applier seat3. The inner peripheral surface5ais provided with key ridges5b. The key ridges5bare formed along the axial direction on the inner peripheral surface5a. The key ridges5bhave a shape adapted to be fitted in the keyways3c. As the key ridges5bengage the keyways3b, the operating unit5is fitted on the elasticity applier seat3in a manner rotatable integrally with the elasticity applier seat3and relatively movable along the axial direction.

The operating unit5has a flange5c. The flange5cis arranged on the bottom portion of the operating unit5. The bottom portion of the operating unit5is located on the case2bside.

A corrugated washer4is fitted on the elasticity applier seat3. The corrugated washer4is located between the flange3dand the flange5c, and elastically urges the flanges3dand5cin the directions away from each other.

The flange5cof the operating unit5is provided with a rubber ring6. The rubber ring6is mounted on the surface of the flange5copposite to the corrugated washer4with the flange5cinterposed therebetween. The rubber ring6is configured of a rubber material such as chloroprene rubber (CR).

The exterior case7of the electronic apparatus A has an operating unit insertion hole7a. The operating unit insertion hole7ais formed in opposed relation with the variable output device2. The operating unit insertion hole7ahas a diameter larger than the outer diameter of the operating unit5and smaller than the outer diameter of the flange5c. According to this embodiment, the exterior case7makes up a holding member. The operating unit insertion hole7aconstitutes an operating hole.

The circuit board1is arranged at a position in proximity to the exterior case7in the direction parallel to the exterior case7. The circuit board1is fixed on the exterior case7at the particular position. As the circuit board1is mounted this way, a top5dof the operating unit5is projected from the exterior case7. The operating unit5has the top5dthereof projected out of the electronic apparatus through the operating unit insertion hole7a, and arranged with the flange5cin contact with the peripheral edge of the operating unit insertion hole7a. In the process, the corrugated washer4urges the flange5ctoward the exterior case7. As a result, the flange5cis pressed against the portion of the exterior case7on the peripheral edge of the operating unit insertion hole7a. The flange5cis pressed against the peripheral edge of the operating unit insertion hole7athrough the rubber ring6.

Next, the operation of the anti-malfunction mechanism for the variable output device according to this embodiment is explained. As long as the adjusting operation of the variable output device2is not performed by the user, the flange5cof the operating unit5is pressed against the portion of the exterior case7making up the peripheral edge of the operating unit insertion hole7aby the corrugated washer4. In the process, the rubber ring6is interposed between the flange5cand the peripheral edge of the operating unit insertion hole7a. Under this condition, the corrugated washer4is elastically urged so that the operating unit5is pressed against the inner side surface of the exterior case7along the axial direction (direction β inFIG. 3) together with the rubber ring6. As a result, the friction under pressure is generated between the flange5c(rubber ring6) and the peripheral edge of the operating unit insertion hole7a. As a result, the operating unit5is fixed on the exterior case7. Thus, the operating unit5is not easily rotated by an external force other than a substantial one. Also, since the gap between the operating unit5and the operating unit insertion hole7ais hermetically sealed by the rubber ring6, dust, water drips, etc. are kept away from the interior of the electronic apparatus A as long as the adjusting operation of the variable output device2is not performed.

In carrying out the adjusting operation of the variable output device2, as shown inFIG. 5, the user pushes the operating unit5into the exterior case7against the resistance of the corrugated washer4. This operation is enabled by the fact that the operating unit5is mounted on the elasticity applier seat3relatively movable therewith along the axial direction.

Once the operating unit5has been pushed in, a gap is formed between the surface of the rubber ring6and the peripheral edge of the operating unit insertion hole7a. As a result, the operating unit5is unlocked. Under this condition, the user rotates the operating unit5while maintaining the pushed-in state. The operating unit5is mounted on the elasticity applier seat3to rotate integrally therewith. By rotating the operating unit5, therefore, the elasticity applier seat3is also rotated in the same direction. The elasticity applier seat3is mounted on the operating shaft2ato rotate integrally therewith. With the rotation of the elasticity applier seat3, therefore, the operating shaft2ais also rotated in the same direction. As a result, the output (electrical resistance, etc.) of the variable output device2undergoes a change.

Upon confirmation that the output of the variable output device2has changed by the desired amount, the user stops the operation of rotating and pressing the operating unit5. Then, the flange5cof the operating unit5elastically urged by the corrugated washer4is pressed against the peripheral edge of the operating unit insertion hole7a. As a result, the operating unit5is fixed on the exterior case7and thus prevented from rotating. Also, the gap between the operating unit5and the operating unit insertion hole7ais hermetically sealed.

Although an anti-malfunction mechanism for the operating unit of a rotary variable resistor has been explained above in this embodiment, the invention is also applicable to an operating unit of a sliding variable resistor. Specifically, a variable resistor with the resistance value thereof changed by a slide is used as a variable output device. The operating unit mounted on the slide operating shaft portion of the variable resistor makes up an operating unit similar to the one according to this embodiment. The exterior case is provided with a slot in which the operating unit slides.

With this configuration, the friction force generated by the elastically urged corrugated washer brings the operating unit into close contact with the exterior case, thereby preventing the slide operation. Also, the slide-type rotary variable resistor can be operated by sliding while pressing the operating unit.

Unlike the above-mentioned case in which a spring member is made up of the corrugated washer4, the invention can be embodied also by use of a coil spring or other elastic member, such as rubber. Also, the invention can be embodied by using a sponge material instead of the rubber ring6for improved friction coefficient.

According to this embodiment, an inadvertent operation can be prevented in a simple and inexpensive fashion by use of a general-purpose variable resistor. The drip proofness and the dust proofness can also be improved.

Second Embodiment

FIG. 6is an exploded perspective view showing a structure of an anti-malfunction mechanism for a variable output device according to a second preferred embodiment of the invention.FIG. 7is a sectional view showing a state in which the anti-malfunction mechanism for the variable output device according to the second embodiment shown inFIG. 7works to prevent a malfunction.

The second embodiment basically has a similar configuration to the first embodiment. Therefore, in the second embodiment, those component parts similar or identical to the corresponding component parts of the first embodiment are designated by the same reference numerals.

Each variable output device2has an operating shaft2a. The operating shaft2ais projected out of the case2bof the variable output device2. Each operating shaft2ais projected along the direction perpendicular to the surface of the circuit board1. The operating shaft2ahas the flange2c. The flange2cis arranged in the vicinity of the surface of the case2b. In view of the fact that the operating shaft2ahas the flange2c, the surface portion of the case2bis stepped. The operating shaft2a, though cylindrical in shape, is cut away in an arcuate fashion along the axial direction and therefore has a D-shaped cross section.

The anti-malfunction mechanism for the variable output device, according to this embodiment, comprises protective members10, spring bearing members11, coil springs12, operating units13and a holding plate14.

Each protective member10includes a disk portion10aand a short cylindrical portion10b. The disk portion10ais coupled to one end of the short cylindrical portion10b. The disk portion10acloses the end of the short cylindrical portion10b. The size of the short cylindrical portion10bis set in the manner described below. Specifically, the short cylindrical portion10bhas an inner diameter somewhat larger than the outer diameter of the flange2cof the operating shaft2a. The short cylindrical portion10bhas an axis about several mm longer than that portion of the flange2cof the operating shaft2awhich is projected from the case2b. The short cylindrical portion10bhas a shaft insertion hole10c. The shaft insertion hole10cis formed concentrically with the short cylindrical portion10b. The shaft insertion hole10cis sufficiently large to allow the operating shaft2ato be inserted therethrough.

Each protective member10is arranged with the short cylindrical portion10bthereof directed toward the flange2c, and under this condition, the operating shaft2aallows itself to be inserted through the shaft insertion hole10c. As a result, the protective member10is mounted on the variable output device2. The protective member10is brought into contact with the surface of the case2bwithout contacting the flange2cof the operating shaft2a. In this way, the protective member10is mounted on the operating shaft2a. Thus, the flange2cof the operating shaft2ais accommodated in the short cylindrical portion10band physically protected.

Each spring bearing member11includes a disk portion11aand a short cylindrical portion11b. The disk portion11ais coupled to an end of the short cylindrical portion11b. The disk portion11acloses the end of the short cylindrical portion10b.

The disk portion11ahas a shaft insertion hole11c. The shaft insertion hole11cis formed concentrically with the disk portion11a. The shaft insertion hole11chas the shape and size described below. Specifically, the shaft insertion hole11chas such a shape and size that the spring bearing member11is movable relatively with respect to the operating shaft2aalong the axis of the operating shaft2a, while the spring bearing member11rotates in operatively interlocked relation integrally with the operating shaft2a.

The size of the short cylindrical portion11bis set in the manner described below. Specifically, the short cylindrical portion11bhas a sufficient inner diameter to accommodate the coil spring12. The short cylindrical portion11bhas an axis about several mm shorter than the axis of the coil spring12. The short cylindrical portion11bhas a sufficient axial length to protect the coil spring12while at the same time securing the extension/contraction stroke thereof.

The outer peripheral surface of the short cylindrical portion11bhas a circumferential shape. The outer peripheral surface of the short cylindrical portion11bhas keyways11d, which are formed along the axial direction of the short cylindrical portion11b.

Each spring bearing member11is arranged with the disk portion11adirected toward the protective member10. Under this condition, the operating shaft2aallows itself to be inserted through the shaft insertion hole11c.As a result, the spring bearing member11is mounted on the variable output device2.

The coil spring12has such a diameter as to allow the operating shaft2ato be inserted through it on the one hand and allow itself to be accommodated in the short cylindrical portion11bon the other hand. The coil spring12, while being accommodated in the spring bearing member11, is mounted on the outer periphery of the operating shaft2a.

Each operating unit13includes a disk portion13a, a short cylindrical portion13band a flange portion13c. The disk portion13ais coupled to an end of the short cylindrical portion13b. The disk portion13acloses one end of the short cylindrical portion13b. The flange portion13cis coupled to the other end of the short cylindrical portion13b. The flange portion13cis extended diametrically outward of the other end of the short cylindrical portion13b.

The size of the short cylindrical portion13bis set in the manner described below. Specifically, the short cylindrical portion13bhas an inner diameter sufficiently large to accommodate the spring bearing member11. The short cylindrical portion13bhas an axial length substantially equal to that of the coil spring12.

The inner peripheral surface of the short cylindrical portion13bis provided with key ridges13dalong the axial direction. The key ridges13dare formed along the axis of the short cylindrical portion13b. The key ridges13dhave such a shape that they are fitted in the keyways11d.

A metal sheet15is mounted on the surface of each disk portion13alocated on the bottom of the short cylindrical portion13b. The metal sheet15is configured of a metal such as stainless steel, aluminum or copper. The metal sheet15is arranged along the disk portion13a. The metal sheet15is molded integrally with the operating unit13. The metal sheet15is exposed to the bottom of the short cylindrical portion13b.

Each operating unit13is fitted on the spring bearing member11with the short cylindrical portion13bthereof accommodating the coil spring12, the spring bearing member11and the operating shaft2a. In the process, the operating unit13, with the key ridges13dengaging the keyways11d, is mounted relatively movably along the axis of the operating shaft2ain a way adapted to rotate integrally with the spring bearing member11. The coil spring12is in contact with the metal sheet15.

The flange13cof each operating unit13has a rubber ring18. The rubber ring18is mounted on that surface of the flange13con the side of the short cylindrical portion13b. The rubber ring18is composed of a rubber material such as chloroprene rubber (CR).

A holding plate14is sufficiently large to cover one or a plurality of variable output devices2mounted on the circuit board1. The holding plate14has operating unit insertion holes14a. The operating unit insertion holes14aare formed at positions each in opposed relation with the corresponding variable output device2. The operating unit insertion holes14aeach have a diameter larger than the outer diameter of the corresponding operating unit13and smaller than the outer diameter of the corresponding flange13c. The operating unit insertion holes14aconstitute operating holes.

The holding plate14is fixed by fixing screws20on the circuit board1through supports16. The holding plate14, with the supports16interposed in the space with the circuit board1, is mounted parallel to the circuit board1in spaced relation with the circuit board1. The holding plate14is mounted on the circuit board1with the operating units13inserted in the operating unit insertion holes14aand the flange portions13cengaging the peripheral edge of the operating unit insertion holes14a, respectively.

The operating units13are elastically urged toward the holding plate14by the coil springs12. The flange portion13cof each operating unit13thus elastically urged engages the peripheral edge of the corresponding operating unit insertion hole14a, whereby the operating units13are supported between the holding plate14and the circuit board1.

In the configuration according to this embodiment with the operating units13mounted as described above, the height of each support16is set in the manner described below. While being elastically urged by the coil springs12, a small gap (about several mm) is required between the bottom of the disk portion13aof each operating unit13and the short cylindrical portion11bof the corresponding spring bearing member11. This gap is required to accommodate the operating stroke of the operating units13. The supports16have a sufficient height to form the particular gap.

The holding plate14has a drip-proof buffer member17. The drip-proof buffer member17is arranged on that surface of the holding plate14which is on the far side from the circuit board. The drip-proof buffer member17is attached substantially over the entire surface described above.

The circuit board1, on which the operating units13, the coil springs12, the spring bearing members11and the protective members10are mounted, is mounted on the inner surface of an exterior case19by the holding plate14. The circuit board1is arranged substantially parallel to the inner surface of the exterior case19of the electric apparatus A. The exterior case19is provided with the operating unit insertion holes19a. The operating unit insertion holes19aare each formed at such a position as to be opposed to the corresponding operating unit13when the circuit board1is mounted on the exterior case19. The circuit board1is mounted on the exterior case19with the top of each operating unit13projected out of the exterior case19through the corresponding operating unit insertion hole19a. With the circuit board1mounted on the exterior case19, the drip-proof buffer member17is in contact with the inner surface of the exterior case19. As a result, the gap between the peripheral edge of each operating unit insertion hole19aand the holding plate14is hermetically kept sealed off from the outside of the exterior case19.

Next, the operation of the anti-malfunction mechanism for the variable output device according to this embodiment is explained. As long as the adjusting operation of the variable output device2is not performed by the user, the flange13cof each operating unit13is pressed against the holding plate14at the peripheral edge of the corresponding operating unit insertion hole14aby the corresponding coil spring12. Under this condition, the operating units13are pressed against the inner side surface of the holding plate14along the axial direction (direction β in the drawing) together with the rubber rings18by the elastic force of the coil springs12. As a result, pressure friction is generated between each flange13cand the peripheral edge of the corresponding operating unit insertion hole14a. The particular operating unit13thus is fixed on the holding plate14and is prevented from being rotated by an external force other than a substantial one.

In performing the adjusting operation of the variable output device2, as shown inFIG. 7, the user pushes the operating units13into the exterior case19against the resistance of the coil springs12. This operation is enabled by the fact that the operating units13are mounted relatively movably along the axial direction with respect to the spring bearing members11, respectively. Once the operating units13are pushed in, a gap is generated between the surface of each rubber ring18and the peripheral edge of the corresponding operating unit insertion hole14a. As a result, the operating units13are released from the fixed state. Under this condition, the user rotates the operating units13while maintaining the pushed-in state thereof. The operating units13are mounted to integrally rotate with the spring bearing members11, respectively. With the rotation of the operating units13, therefore, the spring bearing members11also rotate in the same direction. Each spring bearing member11is also mounted to rotate integrally with the operating shaft2aassociated therewith. With the rotation of a spring bearing member11, therefore, the corresponding operating shaft2aalso rotates in the same direction. As a result, the output (electrical resistance, etc.) of the variable output device2undergoes a change.

Upon confirmation that the output of a variable output device2has changed by a desired amount, the user stops the operation of both rotating and pressing the corresponding operating unit13. Then, the flange13cof the operating unit13under the effect of the elasticity of the coil spring12is pressed against the peripheral edge of the corresponding operating unit insertion hole14a. As a result, the particular operating unit13is fixed by the holding plate14and stops rotating.

According to this embodiment, the protective members10, the spring bearing members11, the coil springs12and the operating units13are fixed on the circuit board1by the holding plate14, thereby assembling these component parts10to13on the circuit board1. After the component parts10to13are assembled on the circuit board1, the circuit board1is mounted on the exterior case19.

The holding plate14for fixing the component members10to13on the circuit board1is comparatively small in size. Therefore, the job of assembling the component parts10to13on the circuit board1using the holding plate14is comparatively easy. Further, the circuit board1can also be mounted on the exterior case19with comparative ease as this job is carried out after assembling the component parts10to13on the circuit board1. As described above, according to this embodiment, both the working efficiency for assembling the component parts10to13on the circuit board1and the working efficiency for mounting the circuit board1on the exterior case19are improved, and therefore the productivity of the apparatus is improved as a whole. Also, in view of the fact the component parts10to13are assembled integrally as a unit on the circuit board1, the component parts10to13can be handled easily at the time of manufacture and repair.

As long as the operating knobs13are not manipulated, the gaps between the operating unit insertion holes19aformed in the exterior case19and the operating units13are hermetically sealed by the drip-proof buffer member17and the rubber rings18, respectively. Therefore, both dust and water drips are kept away from the interior of the exterior case19.

The operating shaft2aof each variable output device2, together with the flange2c, is protected physically by the corresponding protective member10. Therefore, the spring bearing member11is brought into contact with only the protective member10without coming into contact with the operating shaft2a. The force generated by pressing the operating unit13is transmitted to the case2bof the variable output device2through the protective member10but not to the operating shaft2a. The case2b, which is configured of a material such as a metal having a comparatively high physical strength, is not easily damaged even under a sustained external force applied thereto by the press operation of the operating unit13. For this reason, according to this embodiment, a high durability of the variable output device2can be maintained. Also, the configuration in which no external force is applied to the operating shaft2afacilitates the load management of each variable output device2.

Each coil spring12has a very high durability, and therefore is not substantially buckled even under a sustained application of pressure of about 4 kg thereto. The pressure of about 4 kg is an almost maximum load which the user may ever apply to the operating unit13. In this embodiment, using the coil springs12as elastic members secures a high durability.

The metal sheet15is integrally formed in each of the operating units13, and the coil spring12is supported by the metal sheet15. Generally, each operating unit13is configured of a resin mold for its low manufacturing cost. In the case where the coil spring12is supported by this operating unit13, the durability of the operating unit13may be adversely affected. To improve the durability, it can be considered that the operating units13are made of a metal. However, it inconveniently increases both the manufacturing cost and the apparatus weight. According to this embodiment, the use of the metal sheet15not only suppresses the increase of both the cost and weight of the apparatus, but also improves the durability of the operating units13.

According to this embodiment with the coil springs12built in, the end portion of each coil spring12may be caught by the end corner of the corresponding short cylindrical portion11bwhen pressed by the user, thereby giving rise to the chance of making it impossible to move the operating unit5smoothly. In view of this, according to this embodiment, a taper11eis formed on the inner surface of the end portion of each short cylindrical portion11b. As a result, the end portion of the coil spring12is hardly caught by the end corner of the short cylindrical portion11b, thereby maintaining smooth movement of each operating unit5.

To permit the user to smoothly rotate each operating unit13, smooth relative rotation between each spring bearing member11and the corresponding protective member10is necessary. According to this embodiment, the lubricity of the protective member10is improved by subjecting each protective member10to the dry lube baking finish or fluoric resin coating. As a result, the spring bearing member11and the protective member10are rotated smoothly relative to each other.

The elastic force generated by each coil spring12is set in the manner described below. Specifically, in order to prevent the operating unit13from being unduly rotated, each rubber ring18is required to be pressed against the holding plate14under the load of 800 g by the coil spring12. Taking the durability of the holding plate14, the circuit board1and the exterior case19formed of resin or the like into consideration, on the other hand, the load imposed on the holding plate14by the coil springs12is required to be not more than 5 kg. According to this embodiment, this load is set to 2.2 kg taking the aforementioned loading range into account.

In this embodiment, a plurality of minuscule protrusions13eare formed at the top of each operating unit13(the surface of each disk portion13a) in order to assure the rotational operation of the operating unit13by the user.

In the first and second embodiments, the rubber rings18and6, if kept in contact with the holding plate14or the exterior case7over a protracted period of time, may be closely attached to the holding plate14or the exterior case7, respectively. The operating units13and5, if pressed by the user under this condition, would come off from the exterior case7or the holding plate14, as the case may be, abruptly instead of gradually. Then, a large operating sound would be inconveniently emitted at the time of separation.

The unintentional rotation of the operating units13and5can be prevented conveniently by mounting the rubber ring18on both the operating unit13and the holding plate14, and the rubber ring6on both the operating unit5and the exterior case7. In that case, however, the rubber rings18or6may be closely attached to each other and a large operating sound is liable to be generated at the time of separation.

In view of this, according to the first and second embodiments, the rubber rings18and6are mounted only on the operating units13and5, respectively, but not on the holding plate14or the exterior case7. As a result, the operating sound can be suppressed at the time of separation of the operating units13and5from the holding plate14or the exterior case7, respectively, while at the same time positively preventing the unintentional rotation of the operating units13and5.

Especially in the case where the holding plate14is made of a metal in the second embodiment, the rubber ring18is preferably mounted on the operating unit13. This is because the rubber ring18can generate a larger friction force in contact with a metal plate than in contact with a resin. The provision of the rubber ring18on the operating unit13generates a large friction force by contacting the holding plate14of a metal. The rubber ring18, if mounted on the holding plate14, on the other hand, comes into contact with the operating unit13made of a resin, and therefore cannot generate a large friction force. From the viewpoint of a lower manufacturing cost and a smaller weight, it is common practice to form the operating unit13of resin.

In order to suppress the operating sound further, the first and second embodiments employ CR for the rubber rings6and18, respectively. The CR has a properly rough surface, and therefore the rubber rings18and6are not easily attached closely to the holding plate14or the exterior case7, respectively. As a result, the operating sound is emitted less often at the time of separation of the rubber ring18and6. To make it more difficult for the rubber rings18and6to closely attach to the holding plate14or the exterior case7, the surface of the rubber rings18and6is preferably embossed.

A modification of the second embodiment is shown in FIG.8. This modification employs a coil spring12and has a basic configuration similar to that of the second embodiment described above. In the other modifications explained below with reference toFIG. 8, therefore, the component parts having a similar configuration are designated by the same reference numerals, respectively, and are not explained. In this modification, the spring bearing member11is done without, and, as an alternative, a shaft mounting cylinder13fis provided on the operating unit13. The shaft mounting cylinder13fis arranged concentrically in the short cylindrical portion13b. The shaft mounting cylinder13fis formed integrally with the disk portion13a. The inner peripheral surface of the shaft mounting cylinder13fhas the same shape as the outer peripheral surface of the operating shaft2a. As a result, the shaft mounting cylinder13fcan be moved relative to the operating shaft2aalong the axis thereof, and both can rotate integrally with each other. This configuration also can produce a similar effect to the second embodiment. The shaft mounting cylinder13fis formed integrally with the disk portion13aas shown in FIG.8. In the configuration shown inFIG. 9, however, a shaft mounting cylinder13f′ is alternatively formed as an entity independent of the disk portion13a, and then bonded to rotate integrally with the disk portion13a. Any one of these two configurations may be employed with equal effect.

InFIGS. 8 and 9, reference numeral2drepresents a projected edge. The projected edge2dis provided along the outer periphery of the coil spring contacting surface of the case2b. The projected edge2dis projected outward from the coil spring contacting surface in the axial direction of the operating shaft2ato prevent the coil spring12from coming off from the case2b.

The preferred embodiments of the invention have been described in detail above. Nevertheless, the combination and arrangement of the component parts, according to the preferred embodiments of the invention, are variously modifiable without departing from the spirit and scope of the invention set forth in the appended claims.