Electromotive adjustable resistor

Abstract: The electromotive adjustable resistor of present invention comprising, a first worm gear fixed on the motor shaft of the electric motor, a first gear shaft having a first worm wheel and a first cylindrical gear fixed on it, said first worm wheel engaging with the first worm gear, a second gear shaft having a second cylindrical gear and a second worm gear fixed on it, said second cylindrical gear engaging with the first cylindrical gear, an adjustable resistor having a resistance adjusting shaft, a second worm wheel assembled concentrically around the adjusting shaft of the adjustable resistor, said second worm wheel engaging with the second worm gear, means which transmit the rotational torque of the second worm wheel to the resistance adjusting shaft of the adjustable resistor. That is, the gear train of the electromotive adjustable resistor of the present invention comprises two worm gear engagements and a sylindrical gear engagement. A sylindrical gear engagement makes the space between the resistance adjusting shaft and the motor shaft along the axis of the both shafts. So that the axis of the both shafts can be coinside or nearly coinside with, in compliance with the design request, without interference between them. This makes the width W of the electromotive adjustable resistor smaller, and makes the space on the circuit board occupied by it also smaller compared with the conventional type which is not able to coinside the axis of the both shafts.

Description: BACKGROUND OF THE INVENTION This invention relates to an electromotive adjustable resistor which is adapted to be fixed on a circuit board in an electronic apparatus. The resistance of the adjustable resistor is changed by rotating an adjusting shaft thereof by electromotive force or by manual operation. Figures 4, 5, 6 show a conventional electromotive adjustable resistor. In Figure 5, a gear case 2 is covered by a steel plate 1. An adjustable resistor 3, having a resistance adjusting shaft 4 extending through said steel plate 1, is fixed to the steel plate 1. A driving assembly 6 is fixed to the resistance adjusting shaft 4 extending into the gear case 2. A worm wheel 9 is mounted on the resistance adjusting shaft 4 and biased to the driving assembly 6 by a spring 8. The worm wheel 9 and the driving assembly 6 are coupled frictionally so that the transmission of a rotating torque between them is possible. A pad 11 is inserted to stabilized the frictional condition. Another worm gear 13 is fixed on the shaft 12A of an electric motor 12. In Figure 6, which is a sectional view along line A-A of Figure 5, a gearshift 19 is rotatively mounted on an axis CC having a worm wheel 14 and a worm gear 15 fixed thereto. The rotation of the motor shaft 12A is transmitted to the worm wheel 9 via worm gear 13, worm wheel 14 and worm gear 15. As shown in Figure 5, the rotating torque of the second worm wheel 9 is transmitted to the driving assembly 6 through the friction coupling and rotates the resistance adjusting shaft 4, so that the resistance of the adjustable resistor 3 is changed. The resistance of the adjustable resistor 3 is also changed by manually rotating the resistance adjusting shaft 4, extending from the casing of the resistor 3. Upon manual operation, the driving assembly 6 slips with respect to the worm wheel through the pad 11 inserted between them since the worm wheel is blocked against rotation by the worm gear 15. The worm wheel 9 and the worm gear 13 are both arranged in the same plane in order to reduce the size of the gear case 2 but the distance between the axis of motor shaft 12A and resistance adjusting shaft 4 is larger than the sum of the radii of worm gear 13 and worm wheel 9, as shown in Figure 6. Thus, the width W of the conventional electromotive adjustable resistor shown in Figure 5 is comparatively large. In total, the conventional electromotive adjustable resistor occupies comparatively large space on the circuit board to which it is fixed, as shown in Figure 4. It is the object of the present invention to provide an electromotive adjustable resistor which occupies smaller space on a circuit board. SUMMARY OF THE INVENTION The electromotive adjustable resistor of the present invention comprises: a first worm gear fixed on the shaft of an electric motor, a first gear shaft having a first worm wheel and a first cylindrical gear fixed thereto, said first worm wheel engaging with the first worm gear, a second gear shaft having a second cylindrical gear and a second worm gear fixed thereto, said second cylindrical gear engaging with the first cylindrical gear, an adjustable resistor having a resistance adjusting shaft, a second worm wheel mounted on the adjusting shaft of the adjustable resistor, said second worm wheel engaging with the second worm gear, means which transmit the rotational torque of the second worm wheel to the resistance adjusting shaft of the adjustable resistor. That is, the gear train of the electromotive adjustable resistor of the present invention comprises two worm gear engagements and a cylindrical gear engagement. The cylindrical gear engagement defines the space between the two worm gear engagements. That is, the cylindrical gear engagement defines the distance between the resistance adjusting shaft and the motor shaft along the axis of the both shafts. Thus, the axis of both shafts can be coincide or nearly coincide in compliance with the design request, without interference between them. Thereby, the width W of the electromotive adjustable resistor is reduced and the space occupied on the circuit board is also smaller compared to the conventional type in the axis of said shafts are laterally offset with respect to each other. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the side view of the electromotive resistor of the present invention. Figure 2 shows the partial sectional view of the electromotive adjustable resistor of the present invention mounted on a circuit board. Figure 3 shows the perspective view of the electromotive adjustable resistor of the present invention. Figure 4 shows the conventional electromotive adjustable resistor mounted to a circuit board. Figure 5 shows the partial sectional view of the conventional electromotive adjustable resistor. Figure 6 shows a sectional view along the A-A of Figure 5 showing the construction in the gear case of the conventional electromotive adjustable resistor. DETAILED DESCRIPTION OF THE INVENTION Figures 1, 2, 3 show the electromotive adjustable resistor of the present invention. In Figure 1, a gear case 22 is covered by a steel plate 21. As shown in Figure 2, an adjustable resistor 23 having a resistance adjusting shaft 24 extending from both sides of a resistor casing is fixed on the steel plate 21. A driving assembly 26 is fixed on the resistance adjusting shaft 24 which is extending into the gear case 22. A second worm wheel 29 is mounted on the resistance adjusting shaft 24 and biased to the driving component 26 by a spring 28. Said second worm wheel 29 and the driving assembly 26 are frictionally coupled with each other so that transmission of a rotating torque between them is possible. A pad 31 is inserted therebetween to stabilize the frictional condition. A first worm gear 33 is fixed on the motor shaft 32A of the electric motor 32. As shown in Figures 1 and 2, a first gear shaft 41 is mounted in the gear case 22 rotatively in an axis DD and has a first worm wheel 34 fixed thereto, which engages with the first worm gear 33, and a first cylindrical gear 35 also fixed to the shaft 41. A second gear shaft 42 is mounted in the gear case 22 rotatively in an axis EE having a second cylindrical gear 36 fixed thereto, which engages with the first cylindrical gear 35, and a second worm gear 37, which engages with the second worm wheel 29, also fixed to said shaft 42. Thus, the gear train of the electromotive adjustable resistor of the present invention comprises two worm gear engagements and a cylindrical gear engagement. As shown in figure 2, the cylindrical gear engagement defines the space between the two worm gear engagements. That is, the cylindrical gear engagement defines the axial distance between the resistance adjusting shaft and the motor shaft arranged in a common axis. Thus, the axis of both shafts can coincide or nearly coincide , in compliance with the design request, without interference. This makes the width W of the electromotive adjustable resistor smaller, and makes the space occupied on the circuit board also smaller compared to the conventional type. Of course, it is also able to provide an offset of the axis of the motor shaft 32A and the resistance adjusting shaft 24, said offset extending in different directions, as desired. The rotation of motor shaft 32A is transmitted to the second worm wheel 29 via first worm gear 33, first worm wheel 34, first cylindrical gear 35, second cylindrical gear 36, and second worm gear 37. The rotating torque of the second worm wheel 29 is transmitted to the driving assembly 26 through the friction coupling and rotates the resistance adjusting shaft 24, so that the resistance of the adjustable resistor is changed. The resistance of the adjustable resistor 23 is also changed by manually rotating the resistance adjusting shaft 24, extending to the side opposite the gear case 22. In this case, the driving component 26 slips with respect to the second worm wheel 29 due to the pad 31 inserted between them, as the second worm wheel 29 is blocked against rotation by the second worm gear 37. AS shown in Figure 2, the electric connecting terminal 38 is extending to the direction at a right angle to the axis of the resistance adjusting shaft 24 of the adjustable resistor 23, the electric connecting terminal 39 is extending to the direction at a right angle to the axis of the motor shaft 32A, and both electric connecting terminally 38 and 39 are extending to the same direction for the convenience of connecting them to the circuit board. The first gear shaft 41 and the electric connecting terminal 39 both are offset in the same direction with respect to the axis of the motor shaft 32A and the second gear shaft 42 and the electric connecting terminal 38 both are offset in the same direction with respect to the axis of resistance adjusting shaft 24 of the adjustable resistor 23. Thereby the height of the electromotive adjustable resistor is reduced and the center of gravity of the arrangement is closer to the circuit board than is the prior art, so that the electromotive adjustable resistor of the present invention has a small size and has improved resistivity to vibration.

Claims: An electromotive adjustable resistor comprising: an electric motor (32), a first worm gear (33) fixed on the shaft (32A) of the electric motor (32), a first gear shaft (41) having a first worm wheel (34) and a first cylindrical gear (35) fixed thereto, said first worm wheel (34) engaging with the first worm gear (33), a second gear shaft (42) having a second cylindrical gear (36) and a second worm gear (37) fixed thereto, said second cylindrical gear (36) engaging with the first cylindrical gear (35), an adjustable resistor (23) having a resistance adjusting shaft (24), a second worm wheel (29) mounted on the resistance adjusting shaft (24) of the adjustable resistor (23), said second worm wheel (29) engaging with the second worm gear (37), means (26) which transmit the rotating torque of the second worm wheel (29) to the resistance adjusting shaft (24) of the adjustable resistor (23). An electronic adjustable resistor as set forth in claim 1, wherein the torque transmitting means comprise a driving assembly (26) fixed on the resistance adjusting shaft (24) of the adjustable resistor (23), wherein said second worm wheel (29) and the driving assembly (26) are coupled frictionally, so that the transmission of rotating torque between them is possible. An electromotive adjustable resistor as set forth in claim 2, having means (28) which reinforces the contacting pressure between the second worm wheel (29) and the driving component (26). An electromotive adjustable resistor as set forth in claim 1 or 2, wherein electric connecting terminals (39) of the electric motor (32) extend at a right angle to the axis of the shaft (32A) of the electric motor (32), electric connecting terminal (38) of the adjustable resistor (23) extend at a right angle to the axis of the resistance adjusting shaft (24) or the adjustable resistor (23), and said both electric connecting terminals (38,39) are extending to the same direction, the first gear shaft (41) and the electric connecting terminal (39) of the electric motor (32) both are offset in the same direction with respect to the axis of the motor shaft (32A) of the electric motor (32), the second gear shaft (42) and the electric connecting terminals (38) of the adjustable resistor (23) both are offset in the same direction with respect to the axis of the resistance adjusting shaft (24) of the adjustable resistor (23).

Inventors: MATSUI HIROSHI, NAKAGAWA YOSHINOBU, MATSUI, HIROSHI, NAKAGAWA, YOSHINOBU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: H01C1
IPC codes: H01C10