Abstract:
An apparatus is presented which will automatically lap involute and  strai internal or external gear splines. Lapping force is applied alternatively to the left and right side of each tooth flank. Automatic indexing to new radial positions about the circumference of a gear after any preselected number of lapping cycles accomplishes the application of equal lapping forces to each tooth. 
     The apparatus comprises a bed or support frame upon which is mounted a headstock assembly and a tailstock assembly. Mating workpieces, e.g., mating involute or straight internal or external gear splines, are fastened through collets to the mechanisms of the headstock and tailstock assemblies. The tailstock assembly includes a mainshaft attached to the collet holding its workpiece. The mainshaft is driven by a pneumatic piston to reciprocate along the axis of the workpiece causing the workpieces to lap one another. Equal lapping force to each tooth flank is maintained during lapping cycles by a clutch mechanism which transfers a torque along the mainshaft to the workpiece held by the mainshaft as it laps against its mating workpiece held by the headstock assembly. 
     The headstock assembly consists of a transmission which is connected to an indexing mechanism which, between each separate lapping operation, will rotate the workpiece held by the headstock collet an angular distance equal to one tooth spacing. Rotation through increments of one tooth spacing occur automatically after each individual lapping operation until the mating gears have been lapped against one another in all possible orientations between their respective teeth positions. 
     The apparatus produces smooth and consistent gear tooth finishes in a rapid time since the lapping machine maintains proper centerline alignment between mating spline parts throughout all phases of the lapping operations.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     Means for transmitting torque in mechanical devices have always been of great importance. Often, several devices, e.g., axles, must use connectors to transmit torque from one axle to the other or to any third body. Connection means for transmitting torque include gearing, slot and key connections, rigid fastenable couplings, clutch or friction couplings, etc. 
     Spline gears are an important torque transferring device. Large torque components may be transferred via a spline gear connection. In addition, spline gear connections provide the capability of disengaging or engaging the torque transmission at the desire of the operator. 
     The performance of spline gears is dependent upon the precision with which they are prepared. The performance of precision spline gears can be hindered by the presence of excessive friction between the mated spline parts. Interchangeability between lot sizes of production spline parts can be affected by spline tolerances. Undesirable friction may be the result of surface irregularities, burrs, galling, poor or inadequate machining techniques. 
     Methods of finishing the surfaces of spline gears to a precision necessary for their smooth and dependable operation are generally limited to a polishing type procedure known as lapping. Hand lapping is the traditional method applied. Hand lapping is accomplished by mating the female portion with the male portion of the gear, or mating either gear with what is known as a tool which, in reality, is nothing more than the opposite embodiment of the gear. Using a very fine grinding or polishing compound, hand lapping is accomplished by reciprocally sliding the first piece against the second piece, or by sliding the gear in and out of the tool piece. 
     Hand lapping spline parts removes friction, thereby increasing the performance. However, hand lapping operations are inconsistent, monotonous and extremely time-consuming. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the general problem of lapping spline gears. In particular, a spline gear reciprocating lapping machine which automatically laps involute or straight internal or external gear splines is presented. 
     The apparatus is comprised of a tailstock assembly and a headstock assembly which are attached to a main support frame. The headstock assembly is attached to the support frame in a fixed manner. The tailstock assembly is movably attached to the support frame so that it may be moved along an axis common to both assemblies and the spline gears being lapped. 
     The spline gear workpieces are fastened in the headstock and tailstock assemblies by means of appropriate collets. One is fastened in the headstock assembly with its mating opposite fastened in the tailstock assembly. The workpieces may be fastened in the headstock and tailstock assemblies in alternative orientations depending on the operator&#39;s purpose. 
     The headstock assembly holds its workpiece in a firm manner during the lapping process. The assembly is configured to rotate its workpiece about its axis so that between each lapping period the workpiece may be indexed a rotational amount equal to the movement through one gear tooth spacing. Consequently, the workpiece is lapped for each gear tooth spacing through at least an entire revolution about its axis. 
     The tailstock assembly holds its gear workpiece with its axis colinear with the axis of the gear workpiece fixed in the headstock assembly. At the start of a lapping cycle, the tailstock housing moves forward to engage the two workpieces. Automatic lapping is activated wherein a means attached to the tailstock housing moves reciprocatingly along the colinear axis of the mating workpieces causing sliding of one over the other. This process will occur for a set time for each tooth spacing. At the end of such set time, the tailstock system withdraws its workpiece from contact with the mating workpiece held by the headstock assembly and allows the headstock assembly to index its workpiece one tooth spacing. This process is repeated until a complete lapping cycle has occurred. 
     The timing and coordinating control of the operating system is accomplished through a pneumatic system. The pneumatic system also supplies the working energy for lapping the spline parts. Consequently, this pneumatic system is the heart of the spline gear reciprocating lapping machine. It is a compressed air system composed of a network of lines, pressure regulators, air valves, limit control switches and piston driven reciprocating cylinders. 
     The prime advantages of the spline gear reciprocating lapping machine are its speed in lapping operations, its uniform and consistent tooth finishes, its automatic indexing feature for providing positive sequential indexing to any number of radial positions for the workpieces, proper workpiece alignment throughout the lapping operation, and the ability to lap straight internal and external splines as well as involute splines with a defined spiral lead angle rate. 
     OBJECTIVES OF THE INVENTION 
     An objective of the invention is to provide a machine for automatically lapping spline gears. 
     A second objective of the invention is to provide a lapping machine for automatically lapping involute and straight internal or external gear splines. 
     A further objective of the invention is to provide a lapping machine which produces uniform, consistent tooth finishes in a rapid period of time. 
     A further objective of the invention is to present a reciprocating lapping machine which automatically indexes the workpieces relative to one another between lapping cycles to provide positive, sequential indexing to any number of radial positions. 
     Another objective of the invention is to present a reciprocating lapping machine which automatically indexes the relative radial orientation between the workpieces through any preselected number of cycles and which accomplishes the lapping with equal lapping force applied to each tooth. 
     Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the mechanical portion of the lapping machine. 
     FIG. 2 is a semiexploded perspective of the headstock assembly structure. 
     FIG. 3 is a semiexploded perspective of the construction and components of the tailstock assembly. 
     FIG. 4 is a cross-sectional view along the centerline of the tailstock assembly. 
     FIG. 5 is a cross-sectional view along the centerline of the headstock assembly. 
     FIG. 6 shows the headstock assembly and the gear box portion with the indenting mechanism. 
     FIG. 7 is an end on view of the gear box mechanism showing also the pneumatic cylinder for indexing. 
     FIG. 8 is a schematic showing the pneumatic system and controls. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a table 10 or any equivalent platform is used as the basic support for the apparatus. A support frame 12 serves as the functional alignment bed for the apparatus. The area 14 encloses the headstock assembly. Area 16 encloses the complete tailstock assembly. The work area for lapping the spline gears occurs along the axis of the two assemblies between collets 22 and 24. 
     A few select components have been identified on the apparatus in FIG. 1 to help clarify the explanation. In the headstock assembly, a collet 24 is used for holding one workpiece. In the tailstock assembly, a collet 22 holds the mating workpiece, or, in the alternative, it may hold a tool piece for lapping the workpiece held in collet 24. The choice of which collets are to be used for mounting which spline gear workpieces or a toolpiece will be determined by the particular situation or discretion of the operator. 
     Shown in headstock assembly 14 is a housing 18 for a headstock workpiece axle. A detent cylinder 26 holds the rotational orientation of the workpiece in a fixed position during each lapping cycle. 
     Shown in tailstock assembly 16 are a bellows 42, a housing 20 for a tailstock reciprocating mainshaft 28, a clutch assembly 3, a &#34;Lin-Act&#34; alignment coupler 40, a pneumatic actuator cylinder 38, a slipclutch disc 34, an offset follower 32 and an offset follower bar 36. 
     During operation the workpiece held by the headstock assembly is firmly held rigid while the mating workpiece held in the tailstock assembly is slid in and out causing the mating workpieces to lap one another. This lapping action is caused by pneumatic cylinder 38 which through the &#34;Lin-Act&#34; coupler drives reciprocating main shaft 28. This lapping action proceeds for a preselected length of time. 
     Following this the workpiece in the tailstock is withdrawn from contact with the workpiece fastened in collet 24 in the headstock assembly. The headstock assembly then causes its workpiece to be rotated or indexed an angular movement about its axis equivalent to the spacing of one tooth. Upon completion of indexing, detent cylinder 26 in contact with a ball pin mechanism holds the orientation of the headstock workpiece firmly while the next cycle of reciprocal lapping of the workpieces occurs. These processes continue until lapping has occurred for each tooth of the headstock workpiece. 
     Not shown in FIG. 1 nor claimed are systems for supplying a lapping compound to flow over the workpieces while the lapping process proceeds. Also not shown would be guard plates mounted over the work area to protect the operator and to hold any splashing within the confined work area. The purpose of bellows 42 is specifically to protect and insulate the forward end of shaft 28 from being splattered with any fluid delivered to the work area. 
     FIGS. 2, 5, 6 and 7 show more carefully the details of the headstock assembly for two particular embodiments. FIG. 2 shows a semi-exploded view of one embodiment. FIGS. 5, 6 and 7 represent a slightly variated embodiment. The difference basically focuses on the use of different housing brackets for a gear transmission system and index mechanism. 
     Referring to FIG. 2, headstock spindle housing 18 is mounted on a front support bracket 58 and a rear support bracket 60. Hold down brackets 56 are used to secure and fasten the housing to the brackets. In this embodiment an axle 118 is positioned along the working axis of the apparatus and proceeds through housing 18 to connect to collet 24. Upon this axle is mounted the detent cylinder 26, drive gears 82 and 86, and a retainer ring 116. 
     The transmission system includes a transfer gear 78, and gears 80 and 84. The purpose of the transmission system is to provide a means for aiding the indexing of the workpiece held in collet 24 by an angular distance equivalent to one tooth spacing between each lapping cycle. There are two combinations available for indexing in this embodiment. These combinations are governed by the number of indentations on detent cylinder 26. By shifting gears 86 and 82 longitudinally along the working axis the choice of indexing angles is effected as defined by the two rings of indentations on detent cylinder 26. 
     The motive force for indexing comes from a pneumatic cylinder 70 which is attached to the headstock assembly by a base 108. When activated, the pneumatic cylinder rotates an indexing lever 72 through a rotational distance defined by two pneumatic limit control switches 99 and 100. This causes a ratchet gear 74 to index one spacing where it is caught and held by a ratchet 102 and spring mechanism 104. 
     Gears 80, 84, ratchet gear 74 and indexing lever 72 are all mounted on an axle which is mounted between two bearing assemblies 114. Therefore, each index operation drives gears 80 and 84 which in turn may drive their respective mated gears on the working axis the proper rotational distance to index the workpiece one tooth space. 
     The two embodiments displayed in these FIGS. are identical except for differences shown in FIG. 2. Specifically, a bracket 77, bearing assemblies 114, limit control valves 99 and 101, shaft 118, and retainer 116 are unique to this particular embodiment. The alternative general embodiment is displayed in FIGS. 5, 6 and 7. 
     Referring to FIGS. 6 and 7, the second embodiment of the apparatus becomes clear. This embodiment uses a transmission and indexing mechanism housing bracket 76 to support the axle which carries gears 80 and 84, ratchet gear 74 and indexing lever 72. Also supported by this housing is an axle containing gear 78. For this embodiment, and as shown, pneumatic limit control switches 98 and 100 are mounted at the top of bracket 76 to be activated by the top edge of indexing lever 72. 
     The two limit positions for the indexing lever 72 are shown in FIG. 7. The solidly drawn lever 72 represents one limit position while phantom lever 73 represents the other limit position. Shown also is the pneumatic actuating cylinder 70 which drives the lever between its limiting positions when indexing the workpiece. 
     Referring to FIGS. 6, 7, and 8, the mechanism of the ball pin and detent wheel is clearly shown. The detent wheel 26 as explained before consists of separate rows, 64 and 66, of indentations matched to conform with two different tooth spacings for the particular workpieces being indexed. A row of these indentations is aligned with a ball pin 62. Ball pin 62 is mounted in support bracket 60. The tension or force necessary to hold the pin in any indentation on the detent wheel is provided by a spring 68. When the ball pin is properly forced against any indentation on the detent wheel the workpiece is caused to be firmly held during a lapping cycle. The force supplied by the ball pin and its spring is sufficient to hold the workpiece firmly during lapping operations but compliant enough to allow the indexing mechanism to rotate the axis the proper amount for the next lapping operation. 
     FIG. 5 and FIG. 6 best display the remaining particularities of this embodiment. Mounted concentric to and along the working axis are a headstock spindle shaft 50, collet 24, a collet chuck 52, a gear shifting spindle 54, gears 82 and 86, detent wheel 26, a retaining ring 88, and cylindrical ball bearing assemblies 94. Collet chuck 52 fastens to collet 24 by screw threads and provides the means for firmly fixing the workpiece in the collet. Gear shift spindle 54 provides the means for shifting gears 82 and 86 back and forth parallel to the work axis in order to slip the detent wheel from one row of indentations to the other row of indentations 64 or 66. Retainer ring 88 screws on to headstock spindle shaft 50 and firmly holds the shaft and ball bearing assemblies 94 within headstock housing 18. Support brackets 58 and 60 are shown. Hold down brackets 56 are also shown. 
     Alignment of the headstock assembly when fastened to support base 12 is accomplished through the use of a square plain parallel key 90. The positioning of this key is shown in FIG. 7 as well as in FIG. 5. 
     In addition FIGS. 2 and 5 show the option of placing a pin 96 which may be inserted through housing 18 into a hole in the headstock spindle shaft for firmly holding the spindle shaft during periods of attaching or removing workpieces. 
     A second square plain parallel key 92 is positioned along the headstock spindle shaft to fix the orientation of detent wheel 26, gears 82 and 86, and gear shifting spindle 54. 
     Details of the tailstock assembly are exhibited by FIGS. 3 and 4 as well as FIG. 1. It is to be noted that FIG. 3 presents a perspective of the tailstock assembly that has been rotated 180° relative to the perspectives displayed by all other FIGS. 
     With reference to these FIGS. a base plate 120 is seen to rest upon support frame 12. A square plain parallel key 154 aligns base plate 120 and the tailstock assembly so that the axis of the workpiece held by the tailstock assembly is colinear with the axis of the headstock assembly. A support bracket 124 and a hold-down bracket 128 fix the position of the rear portion of the tailstock housing to the base plate. A support bracket 126 along with a second hold-down bracket 128 fix the position of the front portion of the tailstock housing. A support bracket 122 along with a hold-down bracket 130 provide a bearing mount for a reciprocating piston rod 168. Piston rod 168 is given a reciprocating action along the axis of the workpiece by pneumatic cylinder 38. Also shown is a piston head 162 within the pneumatic cylinder. The force which causes the reciprocating lapping action originates with pneumatic cylinder 38 and is transmitted to the moving portions of the tailstock assembly through piston rod 168. The piston rod is connected to a reciprocating main shaft 28 through &#34;Lin-Act&#34; alignment coupler 40. 
     The reciprocating main shaft 28 is held and aligned by tailstock housing 20 through two slide spindle bearings 152 which are mounted at both ends of housing 20. Main shaft 28 contains two cam slots machined into its center portion. A linear cam slot 142 allows the lapping of straight spline parts. A spiral, helical cam slot 144 allows the lapping of helical spline gears. The helical slot is machined to the same lead angle rate as the helical spline gear. 
     A cam follower bearing 141, or CAMROL bearing, mounted in a specially machined bolt 140 rides in either slot at the choice of the machine operator. A portion of both slots is machined with added clearance to let the cam follower bearing float enough to allow a slight rotational movement necessary for applying lapping pressure to the workpieces. 
     Consistent lapping pressure is provided to the reciprocating main shaft by clutch assembly 30. Details of the clutch assembly are shown in FIGS. 3 and 4. The clutch assembly is composed of a front clutch pressure plate 132, a rear clutch pressure plate 134, a slip clutch disc 34, a clutch bearing 166, clutch discs 136, 137, 138 and 139, four machine bolts 148, and four springs 150. 
     The slip clutch disc 34 rides in a machined slot on offset follower 32 as the offset follower is guided along offset follower bar 36. During any linear motion of main shaft 28 the offset follower must move along the offset follower bar, and since the offset follower bar is oriented at an angle to the axis of the workpiece, this causes clutch disc 34 to rotate. The rotation of clutch disc 34 causes rotational forces to be applied through the clutch discs 136 and 137 to clutch pressure plates 132 and 134. Lapping pressure is created by this process which may be adjusted by springs 50 to apply more or less torque by turning the four machine screws 148. 
     FIG. 3 also shows a limit control valve 146 which is adjusted to help control the length of the reciprocating stroke. 
     The workpiece is held within main shaft 28 by collet 22, a collet sleeve 160 and a collet lock nut 158. The collet lock nut fastens down against a bellows plate 164 which provides means for fastening bellows 42 to the main shaft. A pin 156 is shown in FIG. 4 which penetrates hold down bracket 128 and inserts into a receiving hole drilled in main shaft 28. The purpose of this pin is to provide a firm means of holding main shaft 28 when physically attaching or removing a work piece to collet 22 in the main shaft. 
     Details of the pneumatic system are laid out in FIG. 8. The pneumatic system is the heart of the spline gear reciprocating lapping machine. It supplies the working energy and controls the timing for quickly lapping and indexing the spline parts. 
     Air enters an input connection 184 located on a combination filter, lubrication and regulator unit 186. Clean, pressure regulated, unlubricated air is tapped from the regulator and supplied to a pneumatic logic counter 188. 
     Air enters a supply manifold 192 when a palm button on valve 190 is pulled. The manifold supplies air to the input ports of four limit control valves 180, 182, 146 and 101 and two four way spool valves 194 and 196. The reciprocating cylinder 38 receives air from four way spool valve 194. With spool valve 194 in the position shown, the piston rod of cylinder 38 retracts. When the cylinder reaches the end of the lapping stroke, limit control valve 180 is actuated and sends an air pilot signal to limit control valve 99 and through a three way spool valve 198 to the pilot port of four way spool valve 194. The spool valve 194 shifts and allows air to pass through a three way spool valve 202 and a needle valve 204 to an extend port 208 in cylinder 38. Cylinder 38 fully extends and contacts limit control valve 182 which sends an air pilot signal to the pilot port of a three way valve 200 and 202, to an input port 212 in pneumatic logic counter 188, and to the pilot port of four way spool valve 194. 
     The spool of four way valve 194 shifts and routes air to a retract port 210 in cylinder 38. Exhaust air from the extend port of cylinder 38 is controlled by needle valve 204 and an exhaust speed control 220. The piston rod 168 of cylinder 38 now retracts and the cycle is repeated. This cycle laps the workpieces and continues until pneumatic logic counter 188 resets or until the palm button on control valve 190 is depressed. 
     The counter display on pneumatic logic counter 188 is preset by the operator to the number of strokes required for optimum lapping. When the number of lapping strokes has been reached, logic counter 188 is reset through a port 216 and sends an output signal through an output port 214 to the pilot port of a three way spool valve 198. The spool of valve 198 shifts position to block the pilot signal from limit control valve 180 to four way spool valve 194, and pneumatic cylinder 38 continues to retract. The limit control valve 146 is actuated when cylinder 38 reaches the fully retracted position. In the fully retracted position of cylinder 38 the splined work pieces are disengaged and rotated one spline tooth by indexing. The limit control valve 146 accomplishes this task by sending a pilot signal through three way valve 200, to the pilot ports of three way spool valve 202, and to four way spool valve 196. The spool of four way spool valve 196 shifts to send air to an extend port 222 of cylinder 70. The spool of three way spool valve 202 shifts to reroute air from needle valve 204 to a needle valve 206. When cylinder 70 extends, the headstock rotates the spline workpiece one spline tooth. When cylinder 70 is fully extended, limit control valve 101 is actuated and a pilot signal is sent to the pilot ports of four way spool valve 196, to three way spool valves 198 and 200, and to reset port 216 of logic counter 188. The spool of four way spool valve 196 shifts to send air to a retract port 224 of cylinder 70. When cylinder 70 is fully retracted, limit control valve 99 is actuated to pass air through three way spool valve 198 to the pilot port of four way spool valve 194. 
     The spool of four way spool valve 194 shifts and allows air to pass through three way spool valve 202 and needle valve 206 to the extend port of cylinder 38. Needle valve 206 is adjusted for slow extension of cylinder 36 to prevent damage to the splined work pieces during engagement. 
     Cylinder 36 continues to extend slowly until the end of the stroke is reached. When the cylinder is fully extended limit control valve 182 is actuated to send air to the pilot ports of three way spool valves 200 and 202, to an input (count) port 212 of logic counter 188, and to the pilot port of four way spool valve 194. The machine is now reset for reciprocating lapping action of the cylinder 38. 
     Lapping and indexing operations will continue automatically until the palm button on valve control 190 is pulled. 
     Clearly safety devices such as a shield designed to fit over the work area may be integrated into this pneumatic circuit. With such safety device integrated, the system can be set to automatically shut down should the safety shield be opened. 
     Also shown on FIG. 8 are ratchet gear 74, ratchet 102, and indexing lever 72 which is moved by the piston rod of actuating cylinder 70. Exhaust speed control valves 226 and 220 control the release of air exhausted from cylinders 70 and 38. Exhaust silencers 228 have been attached to the ports of several valves to likewise control the exhaust of used air from the pneumatic system. 
     Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.