DEVICE FOR AUTOMATICALLY EXPANDING AND CONTRACTING ANTENNA

Abstract: In a device for automatically expanding and contracting antenna in which a rotary member such as a drum or a gear for moving a wire or a rope that works to expand and contract the antenna element, is rotated by a worm (1) and a worm wheel (2) that are driven by a motor, improvement wherein said worm wheel is formed as an intermediate gear unit that has a small-diameter gear unit (3) formed as a unitary structure and that engages with the gear (13) of said rotary member, said intermediate gear unit is allowed to move together with the gear unit support frame (4) that has switch operation unit with respect to a support shaft (9), a limit switch employing a reversing spring is provided in the power-feed circuits that supply power to said motor to turn it in the forward direction or in the reverse direction, resilient arm members (5, 5') are disposed on said limit switch, and said resilient arm members are operated by the switch operation units of said gear support frame.

Description: DE S CR I PT I ON DEVICE FOR AUTOMATICALLY EXPANDING AND CONTRACTING ANTENNA TECHNICAL FIELD The present invention relates to a device for automatically expanding and contracting antenna. More specifically, the in¬ vention relates to a device for automatically expanding and con¬ tracting antenna which is constructed relatively simply and com- pactly in a clutchless manner, which automatically expands and contracts the antenna smoothly, which protects the wire, which is constructed at a reduced cost, which is highly durable, and which, under abnormal conditions, prevents the motor for expan¬ sion/contraction operation from being burned. BACKGROUND ART Automatically expanding and contracting an antenna mounted on an automobile or any other vehicle is to expand and contract the antenna from inside the vehicle such as from inside the driver's room which, in practice, is very useful and has hereto¬ fore been widely employed. In automatically expanding and con¬ tracting the antenna, however, it is generally accepted practice to execute a clutch function when the antenna is fully expanded or is fully contracted to disconnect the drive force from the motor. So far, such a clutch mechanism has chiefly been incor¬ porated in a portion of the rotary member such as a gear that drives for winding the antenna expansion/contraction wire or that drives the operation wire. The clutch is put into oper¬ ation when a rotational resistance (load) greater than a pre- determined value generates in such a portion. Systems which do not employ clutch means have been disclosed in U.S. Patent No. 4,153,825 and JP-AS 57-28962. In the former system, an operation member fitted with a coil spring is mounted on a worm shaft that is driven by a motor being opposed thereto using a support ring, and a switch provided in a circuit for driving the motor in the forward direction or in the reverse direction is turned off by the operation member when an overload is exerted such as when the antenna is fully expanded or is fully contracted. If mentioned in detail, the worm and the operation member fastened to the worm are suppressed by a coil spring so as not to be thrusted in the axial direction by the load of the members at the back of the worm wheel when the an¬ tenna isexpanded or contracted. When the antenna is fully ex¬ panded or is fully contracted, the operation is stopped after the worm wheel and an overload is produced. As the motor cont¬ inues to rotate, therefore, the thrust that exceeds the suppress¬ ing force of the coil spring urges the worm such that any oper¬ ation memberis urged (one operation member is urged toward the coil spring interposed between the operation members at the time of forward rotation, and the other operation member is urged toward the coil spring at the time of reverce rotation), and wherehy the switch is turned off to stop the motor. In the latter system described in JP-AS No. 57-28962, on the other hand, a pair of circuit breakers are provided for a path that supplies electric power to turn in the forward direct¬ ion the motor that drives a wire transfer mechanism which ex¬ pands or contracts the antenna and for a path that supplies electric power to turn the motor in the reverse direction. When the antenna is fully expanded or is fully contracted, a heavy current flows into the power supply path through the circuit breaker; i.e., the power supply path is opened and the motor is stopped. The above circuit breakers are so coupled together that when a contact of one circuit breaker is opened, a reset button of the other circuit breaker is actuated. To realize such an operation, the two circuit breaker cases are coupled together as a unitary structure as shown in Fig. 2 of the above publication, a slidable reset button is provided between the breaker pieces that undergo thermal deformation when a heavy current flows in the cases, anda contact or a terminal of each of the drive power supply paths is provided on the breaker cases, so that the oper- ation is repeated when the antenna is fully expanded or is fully contracted. In the above-mentioned conventional systems, the clutch mehanism requires a considerably great clutch force; i.e., the clutch mechanism has a diameter which is so great as nearly equal to that of the drum. To obtain such a large clutch force, fur¬ thermore, a correspondingly large spring must be incorporated in the drum shaft. Therefore, the drum portion becomes considerably bulky in the axial direction, and the whole mechanism becomes bulky. Furthermore, it becomes difficult to maintain normal oper¬ ation as the clutch force is weakened after the clutch operation is repeated many times or under poor local conditions. In the above-mentioned conventional system disclosed in said U.S. Patent, furthermore, the switching operation or the switch- ing force is obtained in the final output portion necessitating a large and rigid structure. That is, the operation for expand¬ ing or contracting the antenna finally requires an output which is greater than a predetermined value. To switch the clutch operation in the final output portion, furthermore, the members for clutch operation must inevitably be large in size and strong. In the above-mentioned general clutch, for example, the rotary member such as a drum or a gear that is a final output member has a large diameter so that it will not give damage or will not cause deformation to the wire made of a synthetic resin. The clutch mechanism provided in the portion of the final output rotary member must exhibit braking action that meets the final output and, hence, must have a diameter comparable with that of the final output member. Furthermore, the spring employed therein must have a large resilient force; i.e., the spring becomes bulky. In the system of the above U.S. Patent, the worm must produce a considerably large output to drive the rotary wheel, and the operation member and the coil spring provided for the worm shaft via a support ring or the like must be made of a special mater¬ ial having considerably larage strength and become bulky. That is, the coil spring must effectively suppress the generation of thrust caused by the expanding or contracting force for the mem¬ bers at the back of the wheel that corresponds to the final out¬ put and must, hence, be considerably strong. The operation mem¬ bers are assembled employing such a strong coil spring, and be- s comes bulky and rigid. The motor itself receives the load of the coil spring at all times, and directly acts on the final output portion, and must, hence, produce large output. Furthermore, the motor shaft moves during the moment of overload and generates vibration which adversely affects the commutator. The overload 0 directly acts even on the worm, and the teeth must have a suffi¬ ciently large strength. In the system of JP-AS No. 57-28962, the operation is con¬ trolled electrically not mechanically, and in which the movable contact spring which is a circuit breaker must undergo the de- s formation to overcome the action of the reversing spring when a heavy current flows therethrough to heat it. After the antenna is fully expanded or is fully contracted, therefore, a time lag is always involved before the circuit is opened by the circuit breaker and excessive force is always given to the mechanism o during this moment. Therefore, the worm shaft, gear shaft and the mechanism for transferring the wire, that are driven by the motor, must have considerably large strength. Moreover, the first and second circuit breakers provided in the drive power supply .paths are coupled together, and a device having a slid- 5 able reset button is particularly provided between these circuit breakers so that one breaker is reset when other one is opened. Therefore, the mechanism becomes complex and expensive, and generates the heat during the ordinary operation which is not desirable. 0 When the device for automatically expanding and contracting the antenna is mounted on a vehicle, furthermore, there inevit¬ ably develop such abnormal conditions as bending of the antenna element, erroneous operation of the limit switch mechanism, drop in the voltage due to insufficiently charged condition of the 5 car-mounted power source (storage battery), and abnormal condit- ion due to change in environment. To cope with such abnormal conditions, it is necessary to provide a particular protection circuit (fuse or the like). It is, further, necessary to pro¬ vide a timer circuit which secondarily shuts off the power source when an abnormal instruction signal is received from a sensor in the electronic circuit or when a current flows for longer than a predetermined period of current-carrying time, or a shut-off circuit employing a particular bimetal such as of the automatic reset type or the manual reset type. 0 DESCLOSURE OF INVENTION In order to solve problems inherent in the above-mentioned background art, the present invention provides the device which are -described below. s In a device for automatically expanding and contracting antenna in which a rotary member such as a drum or a gear for moving a wire or a rope that works to expand and cantact the antenna element, is rotated by a worm and a worm wheel * that are driven by a motor, the improvement wherein said worm wheel is o formed as an intermediate gear unit that has a small-diameter gear unit formed as a unitary structure and that engages with the gear of said rotary member, said intermediate gear unit is allowed to move together with the gear unit support frame that ■ has switch operation units with respect to a support shaft, a 5 limit switch employing a reversing spring is provided in the power-feed circuits that supply power to said motor to turn it in the forward direction or in the r-everse direction, resilient arm members are disposed on said limit switch, and resilient arm members areoperated by the switch operation units of said gear o support frame. A device for automatically expanding and contracting anten¬ na as set forth above, wherein a reversing spring of each of the limit switches is composed of a bimetal, a control resilient piece is arranged that moves following' the resilient arm member between thecontrol portions formed for the control resilient pieces to limit the operation range when said reversing spring is opened. A device for automatically expanding and contracting anten -na as set forth above, wherein a rigid control operation piece is provided for the resilient arm members that turn on or off the reversing spring of the limit switches, a limit member is movably provided between the control portions formed the control operation pieces to limit the operation range when said revers- ing spring is opened, and said control operation piece is pro¬ vided with a resilient pressing piece that gives frictional re¬ sistance to the motion of said control operation piece. The rotary member such as a drum or a gear is rotated by the worm driven by a motor to deliver or pull the wire or the rope that expands or contracts the antenna element via an inter¬ mediate gear unit which has a worm wheel and a small gear formed together therewith 3jS unitary structure, and whereby the antenna element is expanded or contracted. On the intermediate gear unit is formed a gear frame that has a switch operation unit, the intermediate gear unit being slidable along the support shaft. Under the ordinary driving condition, the worm rotates and the worm wheel is rotated via the intermediate gear unit which receives either one of the thrusts along the support shaft, whereby the switch operation unit of the intermediate gear unit comes into contact with the resilient arm member for the limit switch of the reversing system in the forward or reverse power- feed circuit. When the antenna element is fully expanded or is fully contracted, the rotary member comes into halt. In this case, the worm continues to rotate and the thrust of the inter¬ mediate gear unit increases. The switch operation unit then operates the resilient arm member to operate the reversible mov¬ ing contact of the limit switch; i.e., the contact is opened and the motor comes into halt. The motor is stopped instantaneously after the antenna is fully expanded or is fully contracted. The thrust of the intermediate gear unit rotates the rotary member via a small gear of the intermediate gear unit. The drive torque is greatly reduced by the gear ratio, and the switch operation unit is operated with a thrust produced by a relative- 5 ly small torque relative to the final output (torque for de¬ livering or pulling the wire). For example, when the operation force of the resilient arm member of the limit switch is set to 3 kg, the switch operation unit gains a thrust which just comes into contact with the re- o silient arm member provided the intermediate gear unit is oper¬ ated with a thrust of smaller than 3 kg under the ordinarily driven condition. When the rotary member is stopped after the anttena is fully expanded or is fully contracted, the thrust of the intermediate gear unit increases instantaneously, and the s switch operation unit grains a thrust of greater than 3 kg to operate the resilient arm memebr. Therefore, the rversible mov¬ ing contact is opened to turn the contact off, and the motor is stopped immediately. Furthermore, a control resilient piece that follows the re- o silient arm member is arranged for the resilient arm member of the limit switch, and a control member is slidably provided be¬ tween the control portions of the control resilient piece to limit the operation range when the reversible moving contact is opened. When one resilient arm member turns off the reversible 5 moving contact being operated by the switch operation unit (un¬ der this operation condition, the switch operation unit of the side opposed to the other resilient arm member is retracted), the control member is operated by the control resilient piece of the side that is operated, and the operation range for opening o the reversible moving contact is limited. When the motor is driven by the power-feed circuit via the other contact, the reversible movable contact that remains turn¬ ed off under the above-mentioned limited condition causes the control member to move as control resilient piece of the other 5 side is actuated by the operation of the other switch operation unit. At the same time, the reversible moving contact that had been turned off is reset and limits the operation range for open ing the other reversible moving contact in the same manner as described above. That is, the operation range for opening the s reversible moving contact has such relationship that the revers¬ ible moving contact is reset bythe function of the limit member when the resilient arm member is operated by the operation of the switch operation unit to no more continue the operation of the switch operation unit. As the other side is operated, there¬ o fore, the contact is turned on again, and the power-feed circuits for the motor are alternatingly reversed to establish a mutual relationship. The switch operation unit operates the resilient arm member when the antenna is fully expanded or is fully contracted, or s when an excess load is given to the expansion/contraction drive system, whereby the reversible moving contact is opened and the motor is stopped instantly. Furthermore, when there is no initial operation (e.g., when the motor does not rotate) or when the voltage of the car-mounted power source is so low that the o motor does not produce enough output for the switch operation unit to depress the resilient arm member and that the reversible moving contact does not open, the contact is not mechanically opened and the electric power supplied to the motor is not turn¬ ed off. In such case, a bimetal is employed for the reversible 5 moving contact; i.e., the heat is generated as an excess current flows through the bimetal. Namely, the contact is opened by utilizing the infrecting action of the bimetal to discontinue the supply of the power to the motor. Under the condition where there does not take place any o such mechanical operation, the control resilient piece does not operate the limit member in the operation range for opening the reversible moving contact; i.e., the reversible moving contact is greatly reversed without receiving any limitation at all. Therefore, the electric power is not more supplied, and the re- 5 versible moving contact is not reset by its own force even when the temperature of the bimetal of the reversible moving con¬ tact is lowered. When the other operation is properly carried out, however, the limit member moves and one reversible moving contact that is reversed is pushed back into the operation limit range and is returned. The two reversible moving contacts are not reset by their own forces. When the limit member is operated, however, a lange reversing force of one reversible contact piece causes the other reversible moving contact to be reset. Therefore, either one of the reversible moving contacts establishes the conductive con¬ dition alternatingly. BRIEF DESCRIPTION DRAWINGS The drawings illustrate technical contents of the present invention, wherein: Fig. 1 is a partly cut-away front view illustrating a gen¬ eral constitution according to the present invention; Fig. 2 is a side view of a worm wheel portion; Fig. 3 is a diagram which stepwisely illustrates the on-off operation for the limit switch; Fig. 4 is a plan view illustrating on an enlarged scale another limit switch operation portion of the present invention; Fig. 5 is a plan view similar to Fig. 4 illustrating on an enlarged scale the operation when the antenna is fully expanded under the ordinary operation condition; Fig. 6 is a plan view illustrating on an enlarged scale the condition where the antenna is started to be contracted and the condition where the antenna is fully contracted; Figs. 7(A), 7(B) and 7(C) are plan views illustrating the operation condition under abnormal condition such as of when the voltageof the power source is lowered and the subsequent inflect¬ ing consitions of the reversible moving contact caused by the generation of heat; Figs. 8 and 9 are plan views illustrating on an enlarged scale the repeating operation of the reversible moving contact which is under the inflected condition due to the generation of heat; Fig. 10 is a plan view illustrating on an enlarged scale one embodiment of the present invention; Fig. 11 is a perspective view of Fig. 10. Fig. 12 is a plan view illustrating on an enlarged scale another embodiment of the present invention; and Fig. 13 is a perspective view of Fig. 12. BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will now be described concretely in conjunction with the accompanying drawings. Fig. 1 illustrates general constitution of the device for automatically expanding and contracting the antenna according to the present invention. A wire or a rope (not shown) of which the one connect¬ ed to the upper end of the antenna element 15 that undergoes ex¬ pansion and contraction, is wound on a drum 12 in a case 10 in a customary manner. The drum 12 is provided with a large gear 3 coaxially. To drive the large gear 13 by the motor 18, a worm 1 fitted to the rotary shaft 11 of the motor 18 is brought into engagement with a worm wheel 2 which is engaged with the large gear 13 via an intermediate gear unit having a small gear 13 formed together with the worm wheel coaxially therewith and as a unitary structure. Due to a gear ratio, therefore, the large gear 13 and the drum 12 are driven at a predetermined speed to expand or contract the antenna emlement 15. The intermediate gear unit consisting of the worm wheel 2 and the small gear 3 is peovided together with a gear frame 4 to slide relative to a support shaft 9 that is provided on the case 10. The gear frame 4 is provided with switch operation units 14 and 14 ' in an opposing manner, and resilient arm members 5 and 5 ' are provided between the switch operation unit 14 and 14 ' . Reversible moving contacts 6 and 6 ' are attached to the free ends of the resilient arm members 5 and 5 ' that are folded in a U-shape. The reversible moving contacts 6 and 6 ' in the dia- gramed embodiment form mounting portions 5a and 5a ' that can be inflected toward the side of base ends of the resilient pieces, and are attached to the resilient arm members 5, 5 ' at the mounting portions, and further have contact portions 6a, 6a ' at the front ends thereof. Positions of the shortest distances between the contact points 6a, 6a ' and the mounting portions 5a, 5a ' serve as neutral points, and the contact points 6a, 6a ' are positioned on either side in excess of the neutral points so as to be inflected and urged. According to the pre- sent invention, however, the reversible moving contacts 6 and 6 ' are in no way limited to the above-mentioned type only but may be of the type of a reversing spring using a coil spring or a resilient wire to obtain the same reversing operation. Or, the resilient contact pieces that are always urged to come into contact with the contact points may be turned off by the re- sikient arm member or by the switch operation unit. When the antenna element 15 is fully expanded or is fully contracted, the worm wheel 2, small gear 3 and gear frame 4 that are slidable relative to the support shaft 9 receive the thrust in the axial direction along the support shaft 9. That is, as the motor 18 is rotated in the forward or reverse direction and the antenna is fully expanded or is fully contracted, the drum 12 and the large gear 13 come into halt and the worm wheel 2 cases to rotate. Then, a thrust acts on the worm wheel 2 in the axial direction according to a helical angle (angle of tilted tooth) of the worm 1 that is kept rotated being driven by the motor 18, and the worm wheel 2 is thrusted in the axial direct¬ ion (the direction is reversed depending upon when the motor is rotated in the forward direction or in the reverse direction). Such a thrust is obtained even when the small gear 3 is tilted in the same direction as the plain gear or the worm wheel 2. With the small gear 3 having teeth inclined in the direction opposite to that opf gear of the worm wheel 2, however, the reaction is obtained efficiently under the condition where the worm 1 contitunes to rotate, and the thrust is effectively applied to the gear frame 4. The switch operation units 14 and 14 ' of the gear frame 4 depress the free ends of the resilient arm members 5 and 5 ' in a manner as shown in Figs 3(B) and 3(C) or as shown in Fig. 5 or 6(B), whereby the reversible moving con¬ tact 6 or 6 ' constituting the limit switch is opened to inter¬ rupt the power supply to the motor 18. The power-feed circuits for feeding power from a DC source to the motor 18 are the same as those of the conventional art. As the direction of current for the motor 18 is switched, the motor 18 is rotated in the forward direction or in the reverse direction. The reversible moving contact 6 is provided in one of the power-feed circuits, and another reversible moving contact 6 is provided in the other power-feed circuit, and the two contacts are turned on by the separately provided power source operation switch to feed the power. The resilient arm members 5 and 5 ' represent a sense pres¬ sure (resilient pressure) of the limit switch and operate the sense pressure of the limit switch as shown in Fig. 3 based on the thrust of the worm wheel 2 driven by the worm 1. By utilizing the resilient pressure in the limit switch, therefore, the motor is turned off in response to the thrust in the mechanical system for expanding and contracting the antenna element without requir¬ ing any particular clutch mechanism. That is, the force acting on the worm wheel 2 that rotates the rotary member such as a drum or a gear that is the final output member via the inter¬ mediate gear unit having small gear 3, is considerably smaller than the final output owing to the gear ratio. The thrust obtained by the worm wheel 2 meets the sense pressure of a small limit switch and is suited for operating the small limit switch. That is, no large or strong member or force is required, and exper¬ iments have proved the durability of greater than 200,000 times which is far superior to the durability of the conventional mechanical clutch mechanism. The switch is turned off from the condition shown in Fig. 3(A) to the condition shown in Fig. 3(B) at a moment when the thrust is obtained on the worm wheel 2, and the motor 18 is stopped. Therefore, a strong coil spring needs not be suppressed, and a large pushing force or pulling force does not continuously act on the expansion/contraction wire, contributing to improving the durability of the expansion/ contraction wire eliminating thebuffer mechanism for the ex¬ pansion/contraction wire. The worm shaft may be a generally employed one; i.e., it does not affect the transmission of torque from the motor 18, exhibits good operation characteristics and does not develop any inconvenience. By suitably adjusting the position at which the switch operation units 14 and 14 ' come in contact with the re¬ silient arm members 5 and 5 ' , the ON-OFF operation force can be easily adjusted. Thus, there is realized a mechasnism which main¬ tains the most efficient operability or proper operability that becomes important depending upon the cases. As described above, the worm wheel is operated by the thrust which is considerably smaller than the final output, and there can be used considerably small resilient arm members for oper¬ ating the gear frame and the limit switch so as to be effective- ly incorporated between the worm and the rotary member such as the drum. The whole device for expanding and contracting the antenna can then be realized in a compact size and at a consider¬ ably reduced cost. Fig. 3 illustrates a limit switch having a basic structure according to the present invention, wherein F Fig. 3(A) shows the condition where the resilient arm members 5 and 5 ' are not operated by the switch operation members 14 and 14 ' , and Figs. 3(B) and 3(C) shows the moments at which the contact points of the limit switch are opened when the antenna is fully expanded or is fully contracted or when an excess load is given to the expansion/contraction drive system. Fig. 4 and subsequent drawings illustrate another embosiment of the present invention which carries out proper operation under ordinary operation condition and which further copes with abnor¬ mal conditions (e.g., motor does not rotate) or with such cases where the voltage of the car-mounted power source has so dropped that the operation is not effectively operated. That is, the worm 1, worm wheel 2, large gear 13, small gear 3, gear frame 4, switch operation units 14, support shaft 9, resilient arm member 5 and reversible moving contact 6, are the same as those memtion- ed in conjunction with Figs. 1 to 3. In the embodiment shown in Fig. 4 and in the subsequent drawings, however, control resilient piece 7 and 7 ' are provided to move following the resilient arm members 5 and 5 ' , and a limit member 8 of a U-shape in plane is movably provided between the control portions 7a and 7a ' formed at the ends of the control resilient pieces 7 and 7 ' to limit the operation range when the reversible moving contacts 6 and 6 ' are opened. Furthermore, the reversible moving contacts 6, 6 ' are composed of a bimetal such that they will undergo deformation due to the heat generated when a heavy current flows therethrough. The operation of the device of Fig. 4 under ordinary con¬ dition is as shown in Figs. 5 and 6(B). That is, when the large gear 13 stops, and the worm wheel 2 and the small gear 3 stop, too, under the condition where the antenna element is fully ex- panded and the worm 1 continues to rotate being driven by the motor, then the gear frame 4, worm wheel 2 and small gear 3 slide in the axial direction, whereby one resilient arm member 5 is pushed by one switch operation unit 14 and the reversible moving contact 6 is turned off. The control resilient piece 7 advances 5 following the resilient arm member 5 that is depressed, and the control portion 7a brings the limit member 8 close to the revers¬ ible moving contact 6, such that the reversing operation range is narrowed when the reversible moving contact piece 6 is turned off. That is, when a moving contact of the reversible moving o contact 6 is separated away from the fixed contact point 16 so that the power-feed circuit is opened under the above-mentioned limited condition, then the moving contact is maintained at a position slightly in excess of the neutral point. When the operation for expanding or contracting the antenna 5 element is started (contracted after it is fully expanded or ex- panded after it is fully contracted), the reversible moving con¬ tact 6 of which the off operation quantity is limited causes the other switch operation unit 14 ' to push the other resilient arm member 5 ' . Here, however, one switch operation unit 14 and the s other switch operation unit 14 ' are formed in a gear frame 4 as a unitary structure as shown. As the other switch operation unit 14 ' effects the pushing operation, therefore, the one switch operation unit 14 that had been pushed is now retraced. As the one switch operation unit 14 is retracted, threfore, the o resilient arm member 5 is retracted, too, whereby the mounted portion 5a of the reversible moving cantact 6 moves back in excess of the neutral point. Therefore, the reversible moving contact 6 returns back to the condition of Fig. 4 of before being turnedoff, comes into contact with the fixed contact point s 16 as shownin Fig. 6(A) to establish such a condition that the antenna element is urged in the reverse direction (expanding or contractingdirection) when the motor 18 is operated in the next time. Such an operation is alternatingly repeated, i.e., the or dinary operation is carried our successively to expand or con- o tract the antenna without permitting a heavy current to flow through the reversible moving contact 6, 6 ' and preventing the motor 18 from being burned or damaged. The same operation is carried out even in case, for example the antenna is bent. When the load equal to that of when the 5 antenna-is fully expanded or contracted is exerted despite the antenna element 15 is not in fact fully expanded or fully con¬ tracted, the members up to the worm wheel 2 come into halt des¬ pite the motor continues to rotate, and the thrust is obtained on the worm wheel 2 and on the gear frame 4. Therefore, the re- o versible moving contacts 6, 6 ' carry out the turn-off operation quite in the same manner as described above, and the restoration operation is effected. On the other hand, when the voltage has dropped due to in¬ sufficiently charged condition of the car-mounted power source 5 that supplies power to the motor 18 or due to a change in the external condition, the switch operation unit 14 ' of the gear frame 4 may not work to depress the resilient arm member 5 ' or may be too weak to depress the resilient arm member 5 ' . In such a case, the mounting portion 5a ' of the reversible moving contact 6 ' that is under the on condition as shown in Fig. 7(A) is inflected. As a heavy current flows, therefore, the revers¬ ible moving contact 6 ' composed of a bimetal generates the heat and is inflected. Due to the action of bimetal, therefore, the contact is opened from the fixed contact point 16, and the electric power is no more supplied to the motor 18 as indicated by a solid line in Fig. 7(B). When the one reversible moving contact 6 ' is turned off by the action of the bimetal, however, the limit member 8 is not almost pushed by the control resilient piece 7 ' , and there does not substantially exist any means for limiting the turn-off operation range of the reversible moving contact. Therefore, the reversible moving contact 6 ' is reversed to a degree greater than that of under the ordinary operation condition. When the temperature of the reversible moving piece 6 ' has dropped as a result of the switch-off of heavy current, the re¬ versible moving contact 6 ' is not restored by its own restor¬ ation action despite the temperature has dropped; i.e., the greatly inflected turn-off condition is maintained. The re¬ versible moving contact 6 ' which is under the off condition then undergoes the switch-on operation to urge antenna element 15 in the opposite direction (in the contracting direction when it has been fully expanded or in the expanding direction when it has been fully contracted). The switch operation unit 14 of the opposite side then pushes the resilient arm member 5 with an ordinary force as shown in Fig. 7(C), and the control resilient piece 7 of the opposite side pushes back the reversible moving contact 6 ' that has been greatly inflected to the turn-off condition, in excess of its neutral point via the limit member 8, to be ready for urging the antenna element in the next time. When the normal force of action is not still reached even when the resilient arm member is depressed by the switch oper¬ ation unit of the opposite side due to abnormal factor such as drop of voltage in the power source, the reversible moving con¬ tact is not restored by its own force. Therefore, the revers- s ible moving contact is maintained under the inflected off con¬ dition. The limit member 8 is slid to the opposite side as the reversible moving contact 6 or 6 is inflected by the generation of heat. Being assisted by the restration action of the bimetal when it is cooled, therefore, the action of the limit member 8 o causes the one reversible moving contact that had been maintained under the inflected off condition to be restored. That is, the two reversible moving contacts repeat their operation when they are inflected by generation of heat to establish a relationship that is shown in Fig. 8 or 9. s Figs. 10 and 11 illustrate one of embodiments of the pre¬ sent invention. That is, resilient arm member 5 and 5 ' are provided between the switch operation units 14 and 14 ' provided for the gear frame 4, reversible moving contacts 6 and 6 ' are attached to the ends of the arm members 5 and 5 ' , and the o power-feed circuits are turned on and off to turn the motor in the for-ward direction or in the reverse direction in the same manner as those of up to Fig. 9. According to the embodiment of Figs. 10 and 11, however, a control operation piece 20 is used in place of the control resilient piece 7, a passive portion 20b 5 formed at the middle portion of the control operation piece 20 is positioned between the arm members 5 and 5 ' , and the con¬ trol operation piece 20 as well as the reversible moving contacts 6 are operated by the operational force of the arm member 5 act¬ uated by the switch operation unit 14. Further, the limit o member 8 having a U-shape in plane is slidably moved by the operation portions 20a formed at the tips of the control oper¬ ation piece 20 in the same manner as the embodiment shown in Figs. 4 to 9. The inflecting operation of the reversible moving contacts 6 is finely controlled and adjusted under the operation 5 conditiones by the limit member 8 that is slidably moved, in same manner as that of the embodiment explained in conjunction with Figs. 4 to 9. A resilient pressure piece 21 is suitably arranged for the control operation piece 20 to limit the control operation piece 20 from undesirably moving and to obtain a pro- perly operating rlationship at all times. Figs. 12 and 13 illustrate another embodiment of the pre¬ sent invention, not having said U-shape. INDUSTRIAL APPLICABILITY According to the present invention as explained in the foregoing, there is no need of incorpolating a clutch in the drum portion or in other portions, and switch operation units are employed for a small gear frame which holds an intermediate gear unit that consists of a worm wheel and a small gear formed as a unitary structure to transmit the drive force of the motor to the drum via worm. Furthermore, the limit switch connected to the motor is turned on and off with a relatively small operational force to quickly bring the antenna expansion/ con¬ traction operation into halt. Therefore, the whole mechanism is constituted in a sufficiently compact size. Moreover, durabil¬ ity of the device is no more affected by the clutch mechanism. Accordingly, durability of the device for automatically expand¬ ing and contracting the antenna is improved, no buffer mechanism for protection is required for the expansion/constraction wire (rffpe) , transmission of torque of the motor is not interrupted and the operation performance is not impaired, presenting great advantage. According to the second invention, furthermore, the effect¬ ively operating relationship is maintained even under abnormal conditions where sufficiently large operational force is not obtained for automatically expanding and contracting the antenna that is mounted on the car due to drop in the voltage of a car- mounted power source. Even under ordinary operation conditions, furthermore, the operation range for opening the reversible mov- ing contact that is turned off is limited to maintain an oper- ation relationship easily and properly. Therefore, heat is not almost generated during the ordinary operation but is generated in a limited manner only during abnormal conditions. This makes it possible to prevent the motor from burning, thus preseting great advantages.

Claims: C L A I M S 1. In a device for automatically expanding and contracting antenna in which a rotary member such as a drum or a gear for s movinga wire or a rope that works to expand and contract the antenna element, is rotated by a worm and a worm wheel that are driven by a motor, the improvement wherein said worm wheel is formed as anintermediate gear unit that has a small-diameter gear unit formed as a unitary structure and that engages with the gear o of said rotary member, said intermediate gear unit is allowed to move together with the gear unit support frame that has switch operation unit with respect to a support shaft, a limut switch employing a reversing spring is provided in the power-feed circuit that supply power to said motor to turn it in the forward s direction or in the reverse direction, resilient arm members are disposed on said limit switch, and said resilient arm members are operated by the switch operation units of said gear support frame. 2. A device for automatically expanding and contracting antenna as set forth in claim 1, wherein a reversing spring of each of 0 the limit switches is composed of a bimetal, a control resilient piece is arranged that moves following the resilient arm member of said limit switch, and a limit member is movably provided between " the control portions formed for the control resilient pieces to limit the operation range when said reversing spring 5 is opened. - 3. A device for automatically expanding and contracting antenna as set forth in claim 1, wherein a rigid control operation piece is provided for the resilient arm members that turn on or off the reversing spring of the limit switches, a limit member is movably o provided between the control portions formed for the control operation pieces to limit the operation range when said reversing spring is opened, and said control operation piece is provided with s resilient pressing piece that gives frictional resistance to the motion of said controloperation piece.

Inventors: SUGA MITSUHIRO, SUGA, MITSUHIRO
Applicants: NIPPON ANTENNA COMPANY LIMITED
Application year: 1989
Main classification: H01Q1
IPC codes: H01Q1