TITLE
HIGH TORQUE ORTHOPEDIC CAST CUTTER
BACKGROUND OF THE INVENTION
Field of the Invention [0001] The present invention relates to a medical device for removing hard orthopedic cast bandages.
Description of Related Art [0002] Portable orthopedic cast cutters have been known for many years and have been commonly used for the removal of orthopedic casting bandages from injured limbs. These units usually comprise a battery compartment as well as a DC current motor and a transmission gearbox, which may include various types of mechanical interconnections. The cutters typically include a circular blade which oscillates through a limited angle to cut the resinous cast material. However, the skin and soft tissues remain unharmed due to difference in inertia between the casting material and the skin. [0003] Several patents, namely, U.S. Patent Nos. 4,081,906; 5,878,607; and 4,421,111 disclose cast cutters using customary ratio reduction gear transmissions driven by a low voltage electric motor. These transmission units are commonly used in order to substitute speed with torque. Eccentric cams mounted forwardly in the cutters transform the rotary motion into the desired oscillating motion. However, customary reduction gears are bulky and space occupying. Further, they require additional mechanical connections which ultimately render the transmission compartment noisy, cumbersome and bulky. Thus, existing battery driven devices known to the art also are excessively heavy due to large motors, heavy-duty batteries and cumbersome transmission units in order to obtain the appropriate torque to do the job.
SUMMARY OF THE INVENTION [0004] The present invention addresses the above problems in the art with a compact improved orthopedic cast cutter. The present invention provides a battery operated cast cutter having improved portability. The present invention also provides a cast cutter having an improved, compact transmission for producing high torque. The cutter can of course be used to cut things other than just casts. [0005] In accordance with an aspect of the present invention, the high torque cast cutter is driven by a DC motor having a high speed rotating shaft. That shaft is connected to a rotating planetary reduction gear, which converts the high rotary speed of the shaft to produce speed with high torque. A carrier plate holds the planet gears on one side facing the motor and has an eccentric pin on its other side. The pin drives a cam that will generate an oscillating movement transmitted to the cutting blade. [0006] This arrangement produces a reduction in rotary speed from the motor shaft to the plate through the mechanical connections and gears, while also producing an increased torque to the blade. This allows the use of smaller DC motors and a smaller battery pack unit, therefore improving the portability of the unit over the existing art. [0007] The above, and other aspects, objects, features and advantages of the present invention will be apparent in the following detailed description of an illustrative embodiment which is to be read in connection with the accompanying drawings, wherein: DESCRIPTION OF THE DRAWINGS [0008] Figure 1 is a longitudinal sectional view of high torque orthopedic cast cutter according to the present invention; [0009] Figure 2 is an exploded perspective view of the motor and planetary gear assembly shown in Figure 1; [0010] Figure 3 is a front elevational view of the carrier plate and oscillating assembly taken along line 3-3 of Figure 1, without the surrounding housing; [0011] Figure 4 is a sectional plan view taken through the carrier plate at the transmission pin 7; and [0012] Figure 5 is a rear elevational view of the carrier plate showing the planetary and sun gears.
DETAILED DESCRIP TION OF THE INVENTION [0013] Referring now to the drawings in detail, and initially to Figure 1, a high torque orthopedic cast cutter C constructed in accordance with the present invention is illustrated in Figure 1. Cutter C is a battery powered electric hand operated device which includes a housing 1, of conventional construction, and a circular cutter blade 4. The housing 1 is openable in any convenient manner, and includes a compartment Ib, which contains a series of batteries or a high capacity battery pack. For example, the battery pack can consist of six 1.2 volt MICAD or high capacity MI-MH batteries that have 200OmH each. These types of batteries will produce an output of 7.2 volts from the pack. Preferably, the cutter of the present invention can be provided with a suitable recharging attachment (not shown) which may be plugged into the battery pack in any convenient or known manner for recharging. For example, means can be provided for enabling the device to be mounted in a charging station for charging between uses. The housing may be opened in any convenient manner to permit replacement of the batteries as needed. Preferably, fast chargers having a charging time of twenty minutes or less are used, so that the battery is always available and fully charged between procedures. If desired, a charge indicator can be provided in the housing connected - A -
to the batteries to indicate the remaining electrical charge, in any manner known to those skilled in the art. [0014] Housing 1 contains a central section 2 in which a cylindrical electrical motor M is mounted. The motor preferably is a high speed electric motor, driven at 7.2 volts DC with an output of 4600 rpm and 0.8 hp. The motor is of any convenient known construction and connected electrically by appropriate contacts to the battery pack so that the battery pack Ib supplies power to operate the motor. [0015] Motor 10 includes an output shaft S extending from its front end. That shaft is connected to a sun gear 8 so that the sun gear rotates with the shaft when the motor is operated. [0016] Sun gear 8 is part of a planetary gear transmission system, which includes a carrier plate 6 on which are mounted three planetary gears 8'. The gears are rotatably mounted on shafts extending from the rear face R of a carrier plate 6. The planetary gears are engaged, as seen in Fig. 5, with sun gear 8 in the center. As sun gear 8 rotates, the gears 8' are rotated as well. [0017] Carrier plate 6 is contained within a housing 3, which has an internal surface 3' including gear tooth grooves formed therein which mate with the gear teeth of the planetary gears 8'. Housing 3 is fixed in the housing 1 in any conventional manner so that when the motor 8 is operated, the sun gear 8 drives the gears 8' against the gear teeth on the inner surface 3' of housing 3, with the result that the carrier plate 6 is rotated within the housing 3. [0018] The rotation of the plate 6 in housing 3 is facilitated by the provision of a plurality of ball bearings 10 mounted in the peripheral edge of the carrier plate in any convenient and known manner. These ball bearings engage a raceway in the inner surface of housing 3 at the forward end of the housing, as seen in Fig. 1. This maintains the carrier plate in a fixed longitudinal position, relative to the housing 3, while allowing it to rotate. [0019] The front face F of carrier plate 6 has a drive pin 7 mounted therein extending parallel to the longitudinal axis of the drive shaft S. Shaft 7 carries at its end a ball bearing raceway which is received within a space defined by the fork legs of a yolk 5, as seen in Fig. 3. The yolk 5 is fixed to a rocker shaft 9 mounted in a ball bearing assembly 9' in the front face of the housing. The cutter blade 4 previously described is removably secured in any convenient manner, for example by a releasable nut 4', on the outer end of the shaft 9. [0020] As will be appreciated, the provision of the planetary gear assembly thus described will cause the plate 6 to rotate in the housing 1 at a lower speed than the shaft 5, causing the shaft 7 to circumscribe a circle about the longitudinal axis of the housing 1 and motor M. As the shaft 7 moves in that circle, its engagement through the bearing assembly T with the yolk 5 will cause the yolk to oscillate about the axis of the shaft 9 and thus oscillate shaft 9. This in turn causes the cutter blade to oscillate with a high torque. [0021] The provision of the ball bearings on the periphery of the plate 6 significantly reduces noise and friction and thereby ultimately improves the output torque of the device. [0022] If necessary, the housing 1 maybe provided with ventilation slots (not shown) for the dissipation of heat. [0023] As a result of this construction, the high torque orthopedic cast cutter of the present invention can be made much smaller and lighter than the previously proposed portable devices of this type, while still retaining the high torques necessary to rapidly and safely cut cast materials. [0024] Although the present invention has been described in terms of the foregoing embodiment, such description has been for exemplary purposes only and, as will be apparent to one of ordinary skill in the art, many alternatives, equivalents, and variations of varying degrees will fall within the scope of the present invention. That scope, accordingly, is not limited in any respect by the foregoing description.
