Abstract:
An escapement device has a latch plate interposed between an input and output shaft. The latch plate is pivotably connected to the input and output shafts. The latch plate has a shoulder which abuts a coaxially mounted gear ring. The output shaft is spring loaded to rotate in one direction. The input shaft can be rotated to disengage the shoulder of the latch from one of the gear ring teeth to allow the output shaft to rotate under its spring bias until the output shaft repositions the latch shoulder to reengage another one of the gear ring teeth.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to escapements, and more particularly, to an escapement which allows incremental amounts of motion of an output shaft at a high torque. 
     2. Disclosure Information 
     Escapement devices often use an oscillating member. The oscillating member has a pair of prongs that alternately engage teeth of a rotatable sprocket. The sprocket is rigidly connected to an output member. The output member is often spring biased to rotate such that when the oscillating member swings and disengages its one prong from a tooth of the sprocket, the sprocket immediately rotates until another tooth thereof engages the other prong. Such oscillating devices can be seen in U.S. Pat. No. 3,316,769 issued to Nordin on May 2, 1967; U.S. Pat. No. 2,907,067 issued to Olsen on Oct. 6, 1959 and U.S. Pat. No. 3,063,297 issued to Hyde on Nov. 13, 1962. 
     Other escapement devices have been devised to to eliminate the oscillating pendulum motion. One device is disclosed in U.S. Pat. No. 2,871,702 issued to Tetro on Feb. 3, 1959 which has an output member and an input member both connected to a spring which is preloaded. The input member has a cam which engages an intermediate sliding block which is forced to disengage from varius stops mounted on the escapement housing after a predetermined amount of rotation of the input member. The output member is then free to rotate with the sliding block until the sliding plate reengages a succeeding stop. The input member is again rotated to rewind the spring and disengage the sliding block from the stop. 
     Another sliding block escapement device is disclosed in U.S. Pat. No. 3,640,142 issued to Stafford on Feb. 8, 1972. The Stafford patent discloses an input member which is connected to the spring that drives the output member. 
     SUMMARY OF THE DISCLOSURE 
     According to the present invention, an escapement device has a rotatable input member and a spring loaded rotatable output member. The input and output members are both connected to an intermediate brake member which engages a stationary internally toothed ring that is coaxially mounted thereabout. The brake member is constructed to be disengaged from the stationary ring in response to a predetermined amount of rotation of the input member whereby the output member is free to rotate in response to the spring force by an amount equal to the angular displacement of the input shaft. 
     Preferably, the brake member is pivotably connected to the input member and has a second pivotable connection to the output member offset from the axis of rotation of the connection to the input member. 
     The broader aspects of the invention include an output shaft and an input shaft that are rotatable with respect to each other. The output shaft is urged to rotate in a first direction. A brake member engages the output shaft and has a first condition which prevents rotation of the output shaft and a second condition which allows angular displacement of the output shaft. The brake member is constructed to move from its first condition to its second condition in response to the predetermined angular displacement of the input shaft. The output shaft is biased such that its output torque is greater than the input torque required to be exerted by the input shaft onto the brake member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference now will be made to the accompanying drawings in which: 
     FIG. 1 is a side elevational and partially segmented view of one embodiment of the invention. 
     FIG. 2 is a cross-sectional view taken along the lines II--II shown in FIG. 1 showing the latch member engaging the stop ring. 
     FIG. 3 is a view similar to FIG. 2 showing the latch member disengaged from the stop ring. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring particularly to FIG. 1, an escapement device generally indicated as 10 has an input shaft 12, an output shaft 14 biased to rotate in one direction by spring 16, a latch plate 18 positioned between the input shaft 12 and output shaft 14, and an internally toothed ring 54 secured to a housing 20 that houses the previously mentioned parts. 
     The input shaft 12 is rotatably mounted by bearings 22 interposed between the shaft 12 and end cap 26. The shaft 12 is integral with an enlarged disc 28. The disc 28 has an aperture 30 near its outer periphery that receives a pin 32. 
     Similarly, the output shaft 14 is mounted by bearings 34 within the body portion 36 of housing 20. Torsion spring 16 has one end anchored to flange 38 and housing body 36 and another end secured to the shaft 14. The spring 16 is preloaded to rotate the shaft 14 in one direction (counter-clockwise in FIGS. 2 and 3). The shaft 14 has its inner end fixedly secured to a disc 40 by pin 41. The disc 40 has an aperture 42 therethrough near its periphery which receives a pin 44. 
     As shown clearly in FIGS. 2 and 3, the pin 32 and pin 44 are positioned approximately 180° from each other with respect to the axes of the two shafts 12 and 14. Pin 44 extends through an aperture 46 in latch plate 18. Pin 32 extends through a notch 48 at the edge of latch plate 18. Latch plate 18 has a shoulder 50 at its forward edge. The shoulder 50 is substantially transverse to a line which passes from the shoulder to the center of pin 44. The shoulder 50 normally abuts one of a plurality of teeth 52 of the internally toothed ring 54 as shown in FIG. 2. The ring 54 is bolted, as shown in FIG. 1, between the end cap 26 and body 36 of housing 20 by a plurality of bolts 56. 
     A plate 58 is also secured to the housing by bolts 56. The plate has a central aperture 60 which receives the inner end of shaft 14. The plate also has an arcuate groove 62 which slideably receives pin 44. 
     In operation, shaft 14 is normally held stationary via the rigid connection to the disc 40 which, in turn, is held in place by pin 44 extending from the latch 18. The latch 18 is prevented from rotating by having its shoulder 50 normally abutting one of the teeth 52 of ring 54 as shown in FIG. 2. 
     Input shaft 12 is free to rotate a desired amount in the counter-clockwise direction as viewed in FIGS. 2 and 3. As the shaft 12 rotates, pin 32 revolves about the axis of rotation. The latch 18, engaging the pin 32 via notch 48, is forced to pivot; but, its pivotal axis is not coincident with the axis of rotation of shaft 12. Instead, the latch 18 pivots about pin 44. As the latch pivots about pin 44, the shoulder 50 is moved radially inwardly toward the axis of shaft 12 until shoulder 50 disengages from the toothed ring 19 as shown in FIG. 3. 
     When the disengagement occurs, the spring loaded output shaft 14 is free to rotate counter clockwise under the influence of preloaded spring 16. The spring 16 is preloaded to bias the output shaft in the counter-clockwise direction as viewed in FIGS. 2 and 3. 
     As the output shaft 14 rotates under the spring bias, the pin 44 thereby moves within arcuate groove 62. As the pin 44 moves within the groove 62, it forces the latch plate 18 to pivot about pin 32 until the shoulder 50 reengages another one of the teeth 52. As the shoulder 50 reengages one of the teeth 52, further rotation of output shaft 14 is prevented. The escapement device is thereby ready to repeat the above described operation. 
     The input torque needed to rotate shaft 12 does not have to overcome the spring 16 since rotation of the input shaft 12 does not wind up spring 16. Input (unlatching) torque is only required to be large enough to overcome the friction between shoulder 50 and the teeth 52 of toothed ring 54. Spring 16 is anchored only to the output shaft and the housing. Consequently, the output torque provided by output shaft 14 can be significantly higher than the input torque exerted on input shaft 12. 
     The output shaft is released for incremental amounts of rotation based upon the amount of rotation of input shaft 12 and the spacing of teeth 52. A rotation of input shaft 12 less than the amount needed to disengage the shoulder 50 from one of the teeth 52 produces no motion of output shaft 14. Once the shoulder 50 is disengaged from one of the teeth 52, the output shaft rotates a predetermined minimum amount so that the shoulder engages a successive tooth of ring 54. No smaller amount of rotation is possible for output shaft 16. On the other hand, multiple amounts of the predetermined minimum amount of rotation are possible if the input shaft rotates more than the minimum amount. 
     The total angular displacement of output shaft 16 is controlled by the angular span of the arcuate groove 62. The arcuate groove 62 can be a total circle or an arc spanning any predetermined number of degrees less than 360° whereby the output shaft 14 is allowed to rotate only those predetermined number of degrees before the pin 44 abuts the end 63 of groove 62. 
     In this fashion, an incremental escapement device uses a rotational input shaft rather than an oscillating input device and allows the output shaft to rotate with a high torque compared to the input torque of the input shaft. In addition, the incremental amount of angular rotation is easily predetermined by the spacings of teeth 52. The total amount of rotation is easily determined by the angular span of acruate groove 62. Bolt head 57 (see FIGS. 2 and 3) is the head of a bolt which has been fixedly inserted into disc 40 and slightly protrudes therefrom. One side of bolt head 57 is flat, coinciding with and acting as a stop for one edge of latch plate 18 when the latter is in the engaged position (FIG. 2). This prevents shoulder 50 from engaging too tightly into teeth 52, reducing the wear and tear thereon. 
     Variations and modifications of the present invention are possible without departing from its spirit and scope as defined by the appended claims.