Torque limiter

Abstract: A transmission device (1) has holding slots (1b) provided in a boss portion (1a) thereof for holding engaging means (4), a drive shaft (3) has engaging recesses (6c) provided in an outer surface thereof for accepting partially the engaging means (4) to engage the transmission device (1) with the drive shaft (3), and the engaging means (4) remain urged against the engaging recesses (6c) of the drive shaft (3) by a resilient member (7) which is disposed radially of the boss portion (1a) of the transmission device (1) for maintaining the engagement of the transmission device (1) with the drive shaft (3), so that when the transmission device (1) is overloaded, the engaging means (4) depart from the engaging recesses (6c) in the drive shaft (3), as resisting against the urging force of the resilient member (7), to cancel the transmission of torque from the drive shaft (3) to the transmission device (1).

Description: The present invention relates to an improvement of a torque controller. A conventional torque controller comprises, as shown in Fig. 8, a pair of retaining members 8D, 8D mounted to both ends of a rotary boss 8C joined to a drive shaft 8B of a motor 8A, a transmission device 8E, e.g. a toothed wheel, and two friction plates 8F, 8F which are rotatably fitted onto the rotary boss 8C, and a compression coil spring 8G mounted between one of the retaining members 8D and the friction plate 8F for urging the transmission device 8E and the two friction plates 8F, 8F against the other retaining member 8D. The transmission device 8E is hence engaged by the friction effect of the two friction plates 8F, 8F to the rotary boss 8C. In action, a power of torque is transmitted from the drive shaft 8B to the transmission device 8E through the friction effect. If the transmission device 8E is overloaded, the friction effect is canceled terminating the transmission of the torque. It is however essential for producing a desired strength of friction in the conventional torque controller to optimize the contact area between the transmission device 8E and each of the friction plates 8F. As the result, the overall dimensions of the controller will be increased. In addition, it is known that the transmission of torque through the friction is substantially affected by environmental conditions. Also, the major components of the conventional torque controller are installed as aligned axially of the drive shaft 8B, thus increasing the lengthwise dimension. It is an object of the present invention, in view of the foregoing predicaments, to provide an improved torque controller which is smaller in the dimensions, particularly in the length, and less affected by the environmental conditions during the transmission of torque. A torque controller is disclosed in GB-A-899676 which has a transmission device provided with a center hole into which a drive shaft of a power source is inserted, and engaging means for engaging the transmission device with the drive shaft, in which when the transmission device is overloaded thus to produce a counter torque on the drive shaft, it is automatically disengaged from the drive shaft, the transmission device has holding slots provided in a boss portion thereof for holding the engaging means, the drive shaft has engaging recesses provided in an outer surface thereof for accepting partially the engaging means to engage the transmission device with the drive shaft, and the engaging means remain urged against the engaging recesses of the drive shaft by a resilient member which is disposed substantially radially outwardly of the boss portion of the transmission device for maintaining the engagement of the transmission device with the drive shaft. In action, when the transmission device is overloaded the engaging means depart from the engaging recesses in the drive shaft, as resisting against the urging force of the resilient member, to cancel the transmission of torque from the drive shaft to the transmission device. The invention is characterised in that each said engaging means comprises a pin-shaped member having an inner portion configured to fit in a respective engaging recess, and an outer portion having therein a radial recess extending in a circumferential direction of said boss portion; and in that the resilient ring has a rectangular cross-section including a radial dimension that is greater than an axial dimension, and said ring has a radially inner edge fitting in said radial recess of each said pin-shaped member. More specifically, the torque controller of the present invention allows the transmission device to remain engaged with the drive shaft when it is normally loaded in a common transmission mode with the engaging means being urged by the resilient member towards the engaging recesses of the drive shaft. During the common transmission mode, the drive shaft can transmit a power of torque to the transmission device. If the transmission device is overloaded thus to produce a counter torque on the drive shaft, the engaging means depart from their respective engaging recesses of the drive shaft as resisting against the urging force of the resilient member. As the result, the torque transmission from the drive shaft to the transmission device is interrupted. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional front view of a torque controller; Fig. 2 is a side view of the same; Fig. 3 is an explanatory view of actions of the same; Fig. 4 is a perspective view showing a film conveying unit equipped with the torque controller in a photographic printing machine; Fig. 5 is a cross sectional front view of a torque controller according to the present invention; Fig. 6 is a side view of the same; Fig. 7 is an explanatory view of actions of the same; and Fig. 8 is a cross sectional front view of a conventional torque controller. A torque controller A has a gear 1 (an example of the transmission device) engaged by a ball 4 (an example of the engaging means) to a drive shaft 3 of a motor 2 (an example of the driving source). When the drive shaft 3 is stressed by a large torque due to overloading on the gear 1, its engagement with the gear 1 is released to terminate the action of torque transmission. The drive shaft 3 comprises a motor shaft 5 of the motor 2 and a rotary boss 6. The rotary boss 6 is coaxially fitted onto the motor shaft 5. The rotary boss 6 has a threaded slot 6b provided across a radially enlarged proximal portion 6a thereof. The rotary boss 6 is tightened onto the motor shaft 5 by a screw 8 screwed into the treaded slot 6b. Also, the rotary boss 6 has a pair of ball recesses 6c provided in the outer surface of a distal end thereof for accepting balls 4 with their curved surface. The two ball recesses 6c are equally spaced from each other as in opposite sides of the rotary boss 6. The gear 1 has a pair of ball slots 1b provided in a boss portion 1a thereof for accommodating the balls 4. The two ball slots 1b are also equally spaced from each other as in opposite sides of the boss portion 1a. A projection 1c is arranged on the outer surface of the boss portion 1a of the gear 1 between the two ball slots 1b for protecting a resilient ring 7 from slipping. The gear 1 has a center hole 1d therein into which the rotary boss 6 of the drive shaft 3 is rotatably inserted. The resilient ring 7 (an example of the resilient member) has a slit therein as is formed by rolling a strip of a resilient material. The resilient ring 7 is fitted onto the boss portion 1a of the gear I to cover the ball slots 1b. The resilient ring 7 is restricted at its two ends by the projection 1c of the bass portion 1a. The balls 4 accommodated in the ball slots lb in the gear 1 are seated sectionally in their respective ball recesses 6c of the rotary boss 6. Also, the balls 4 remain urged towards the ball recesses 6c by the resilient ring 7 so that the gear 1 is engaged with the rotary boss 6. While the gear 1 is loaded normally, the urging force of the resilient ring 7 allows the balls 4 to stay in their respective ball recesses 6c for transmission of torque. if the transmission device is overloaded, it causes the balls 4 to depart from the ball recesses 6c of the rotary boss 6 as resisting against the urging force of the resilient ring 7. More specifically, the torque controller maintains the engagement between the gear 1 and the drive shaft 3 with the urging force of the resilient ring 7 during the normal operation of the gear 1 and transmits a power of torque on the drive shaft through the balls 4 to the gear 1. When the gear 1 is overloaded and an excessive counter torque is generated on the drive shaft 3, the balls 4 are released from their respective ball recesses 6c at the drive shaft 3 side thus disengaging the gear 1 from the drive shaft 3 and terminating the transmission of the power of torque. Fig. 4 illustrates the torque controller A installed for use in a film conveying unit of a photographic printing machine. It should be noted that the transmission device is not a gear but a pulley 1. The torque controller A is adapted for preventing a film 2 from being injured by rollers. The film conveying unit is designed for conveying a (negative) film 10A from its cartridge 10B through a transfer path 10C to an exposure station of the photographic printing machine. After the exposure process is completed, the film 10A is returned back to the cartridge 10B. More particularly, the film 10A is rewound on a spool (not shown) of the cartridge 10B with its proximal end joined to the spool. The film 10A is conveyed by a conveying means which comprises drive rollers 10D and press rollers 10E arranged on opposite sides of the transfer path 10C. The drive rollers 10D are driven by a motor 2. A belt 10H is spanned between the main pulley 1 mounted on a drive shaft 3 of the motor 2 and an idler pulley 10F fixedly mounted on a roller shaft 10G of the drive rollers 10D. As the drive shaft 3 of the motor 2 runs, the drive rollers 10D are rotated. The press rollers 10E remain urged by holding means (not shown) such as springs towards the drive rollers 10D. As the drive rollers 10D rotate, the press rollers 10E follow to run directly on the film 10A which is thus conveyed along the transfer path 10C. There is also a detecting means 10H disposed between the conveying means and the cartridge 10B for reading end perforations (not shown) provided in the film 10A from the cartridge 10B (Fig. 4). The end perforations may be read by the detecting means 10H slightly before or after the film 10A is entirely unloaded from the cartridge 10B. The movement of the drive rollers 10D is controlled by a roller controller means 101 which is responsive to a detection signal from the detecting means 10H. The action in the film conveying unit equipped with the torque controller A will now be explained. (1) The film 10A is first unloaded from the cartridge 10B and conveyed by the conveying means to the exposure station for exposure process. (2) If the film 10A continuously runs with its final frame at the exposure station, its perforations are read by the detecting means 10H which in turn sends a detection signal to the roller controller means 101. Upon receiving the detection signal, the roller controller means 101 stops the rotation of the drive shaft 3 of the motor 2 and thus the movement of the drive rollers 10D. (3) In case that the roller controller means 101 fails to stop the motor 2 due to control error or no response to the detection signal from the detecting means 10H, the torque controller A is activated to prevent the film 10A for being damaged by the continuous movement of the drive rollers 10D In other words, when the film 10A has been fully unloaded from the cartridge 10B and is no more conveyed, the pulley 1 is automatically disengaged from the drive shaft 3 and made free from a torque transmitted from the drive shaft. This prevents the film A from being stressed by an excessive tension and separated from its cartridge 10B or injured by the rollers 10D and 10E. (4) After the film 10A is fully unloaded from the cartridge 10B, it is returned back to the same by the reverse movement of the drive rollers 10D. It is understood that the torque controller A is not limited to the installation in the film conveying means in a photographic printing machine. Embodiment Figs. 5 to 7 show a torque controller according to the present invention. The torque controller A of the embodiment is similar to that of Figures 1 to 3, in which a gear 1 is engaged by the engaging means 4 with a drive shaft 3 of a motor 2. When the gear 1 is overloaded, it is disengaged from the drive shaft 3 of the motor 2 to terminate the transmission of torque. In particular, the engaging means 4 are specifically shaped pins, each having a radial recess 4a provided circumferentially in a center region thereof. A rotary boss 6 has a pair of pin recesses 6c for accepting with their arcuate surfaces the pins 4. Also, two holding slots 1b are provided in a boss portion la of the gear 1 for accommodating the pins 4 respectively. A resilient ring 7 has a rectangular shape in cross section, the height being greater than the width, so that it is neatly fitted with its inner edge into the radial recesses 4a of the pins 4. The other components and their construction are identical to those of the torque controller of figures 1 to 3, as denoted by like numerals and will be no more explained. The action of the torque controller A of this embodiment is substantially identical to that of the torque controller of figures 1 to 3 (Fig. 6). When the gear 1 is overloaded, it is disengaged from the drive shaft 3 with the pins 4 departing from their respective pin recesses 6c of the rotary boss 6 and made free from a power of torque on the drive shaft 3 (Fig. 7).

Claims: A torque controller (A) having a transmission device (1) provided with a centre hole into which a drive shaft (3) of a power source (2) is inserted, and engaging means (4) for engaging the transmission device with the drive shaft, in which, when the transmission device (1) is overloaded thus to produce a counter torque on the drive shaft, it is automatically disengaged from the drive shaft, the transmission device (1) has holding slots (1b) provided in a boss portion (1a) thereof for holding the engaging means (4), the drive shaft (3) has engaging recesses (6c) provided in an outer surface thereof for accepting partially the engaging means (4) to engage the transmission device (1) with the drive shaft (3), and the engaging means (4) remain urged against the engaging recesses (6c) of the drive shaft (3) by means of a resilient ring (7) which is disposed substantially radially outwardly of the boss portion (1a) for maintaining the engagement of the transmission device (1) with the drive shaft (3), so that when the transmission device is overloaded, the engaging means (4) depart from the engaging recesses (6c) in the drive shaft (3), as resisting against the urging force of the resilient ring (7) to cancel the transmission of torque from the drive shaft (3) to the transmission device (1), characterised in that each said engaging means (4) comprises a pin-shaped member having an inner portion configured to fit in a respective engaging recess (6c), and an outer portion having therein a radial recess (4a) extending in a circumferential direction of said boss portion (1a); and in that the resilient ring (7) has a rectangular cross-section including a radial dimension that is greater than an axial dimension, and said ring (7) has a radially inner edge fitting in said radial recess (4a) of each said pin-shaped member (4).

Inventors: KOJIMA MASAYUKI, KOJIMA, MASAYUKI
Applicants: NORITSU KOKI CO LTD, NORITSU KOKI CO., LTD.
Application year: 1996
Main classification: F16D7
IPC codes: F16D7, G03B27, B65H23, G03B17, G03B1