Patent Publication Number: US-3874125-A

Title: Convertible pad sander

Description:
United States Patent 11 1 Stroezel 5] Apr. 1, 1975 CONVERTIBLE PAD SANDER 3,136,099 6/1964 Tully et al 51/170 MT Inventor: Reinhold Sneeze], Leinfelden, 3,375,616 4/1968 Scott et a1 51/170 MT Germany Primary Examinerlames L. Jones, Jr. [73] Asslgnee: Robert Bosch GmbH Stuttgart Attorney, Agent, or Firm-Michael S. Striker Germany [22] Filed: Mar. 27, 1974 [57] ABSTRACT A N [21] pp] 0 455286 A sander wherein an electnc motor can rotate a shaft in two directions and the shaft carries an eccentric [30] Foreign Application Priority Data which orbits the pad while the shaft rotates in one di- Mar. 31, 1973 Germany 2316286 reetien and reeiproeates the p while the shaft tates in the opposite direction. Two counterweights [52] US. Cl 51/170 TL, 51/170 MT, 15/22 R rotate about the shaft in the same direction while the [51] Int. Cl. B24b 23/00 pa Orbits, and in pp r t s while h pad [58] Field of Search 51/170 T, 170 TL, 170 MT reciprocates. A change in the direction of rotary 51/170 R; 15/22 R, 50 R, 98 movement of the shaft automatically entails a conversion of orbital movement of the pad into reciprocatory [56] References Cited movement, or vice versa.  
  UNITED STATES PATENTS 20 Claims, 3 Drawing Figures 2.893,]77 7/1959 Bruck 51/170 MT PATENTED APR 1 5 SHLEI 1 BF 2 CONVERTIBLE PAD SANDER BACKGROUND OF THE INVENTION The present invention relates to portable power tools in general, and more particularly to improvements in pad sanders. Still more particularly, the invention relates to improvements in convertible pad sanders wherein the platen and the cushion can perform orbital or reciprocatory movements.  
  It is already known to provide a pad sander with a selector which enables the means for moving the pad to impart to the latter an orbital movement or a reciprocatory movement. It is also known to provide such sanders with two counterweights which are intended to balance the mass of the moving pad. The pad is attached to the housing of the sander by one or more elastic columns or the like. The element which moves the pad is an eccentric driven by the output shaft of an electric motor or another suitable prime mover. One of the counterweights is a flywheel and the other is a balancing beam. When the sander is in use, the center of gravity of the flywheel moves counter to the direction of movement of the center of gravity of the balancing beam. This effects a mere partial balancing of the pad regardless of the setting of the selector, i.e., regardless of whether the pad orbits or reciprocates. Consequently, the manipulation of such sanders necessitates the exertion of a substantial effort because the operator must grip the handle or handles of the power tool with a considerable force. This is tiresome to the user and results in excessive wear upon the parts of the sander.  
 SUMMARY OF THE INVENTION An object of the invention is to provide a convertible pad sander wherein the pad is fully or nearly fully balanced, not only while the pad performs orbital movements but also when the pad is caused to reciprocate with respect to the housing.  
  Another object of the invention is to provide a novel and improved system of counterweights in a convertible pad sander.  
  A further object of the invention is to provide a pad sander whose pad can orbit or reciprocate with novel and improved means for selecting the mode of movement of the pad with respect to the housing.  
  An additional object of the invention is to provide a pad sander wherein the mechanism for transmitting motion to the pad occupies little room, which can be manipulated for extended periods of time with a minimum of effort, and wherein the wear on the moving parts and their bearings is less pronounced than in conventional pad sanders.  
  The invention is embodied in a pad sander which comprises a housing, a pad which is movably coupled to the housing by elastic columns or the like, drive means including a prime mover mounted in or on the housing, an eccentric receiving motion from the prime mover and serving to move the pad with respect to the housing, and control means which is operable to respectively convert the movement of the eccentric into orbital or reciprocatory movements of the pad, a pair of counterweights rotatable in the housing about a common axis to compensate for imbalance of the pad while the pad performs orbital or reciprocatory movements, and means for respectively rotating the counterweights in the same direction and in opposite directions when the pad respectively orbits and reciprocates with respect to the housing. The controol means is preferably operated by mechanical selector means, such as a selector means including a reciprocable plunger installed in a shaft which carries the eccentric and can be driven by the prime mover in two directions through the intermediary of a set of gears.  
  The counterweights and/or their carriers are preferably mounted one behind the other on the shaft which carries the eccentric.  
 The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved pad sander itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.  
 BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary partly elevational and partly longitudinal vertical sectional view of a convertible pad sander which embodies the invention, the parts of the sander being shown in positions they assume when the pad is ready to perform orbital movements;  
  FIG. 2 is a fragmentary sectional view as seen in the direction of arrows from the line II-II of FIG. 1; and  
  FIG. 3 is a fragmentary sectional view as seen in the direction of arrows from the line III-III of FIG. 1.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown a portable power tool which constitutes a pad sander. The sander comprises a housing 10 which is rigid with the casing of a prime mover here shown as an electric motor 11. The casing of the motor 1 l is rigid with a handle 12 receiving one end of a flexible power cord 12a the other end of which carries a plug, not shown, which is insertable into an outlet. A pad 13 including a platen and a cushion of synthetic plastic or other suitable material is movably coupled to the underside of the housing 10 by several elastic columns 14 or in another suitable way.  
  The output shaft 15 of the motor 11 extends downwardly toward the pad 13 and rotates in an antifriction ball bearing 16 of the housing 10. The lower end portion of the output shaft 15 is rigid or integral with two gears 17 and 18. The lower gear 18 is larger than the upper gear 17. A fan 15a is mounted on the output shaft 15 at a level above the bearing 16. In the illustrated embodiment, the gears 17, 18 are integral with each other and are fixedly mounted on the shaft 15 against any angular, axial and/or other movement relative thereto.  
  An intermediate shaft 19 is fixedly mounted in the housing 10. The shaft 19 is parallel to the output shaft 15 and is surrounded by a needle bearing 19a for a small intermediate gear 20 which meshes with the upper gear 17 on the output shaft 15. The gear 20 is freely rotatable on the intermediate shaft 19 but is held against any appreciable axial movement.  
  A further shaft 21 is mounted in the housing 10 in parallelism with the shafts 15 and 19. The upper part of the shaft 21 is mounted in a needle bearing 22 and the lower part of the shaft 21 extends into the inner race of an antifriction ball bearing 23 in the housing 10. That end portion of the shaft 21 which is adjacent to the pad 13 is provided with an eccentric pin 24 located at a level below the bearing 23.  
  A first counterweight or balancing weight 26 is nonrotatably secured to the shaft 21 between the bearings 22, 23 by a radially extending motion transmitting pin 25. The counterweight 26 is inwardly adjacent to a second counterweight or balancing weight 27 which is attached to or made integral with the periphery of a substantially dished lower portion 28a of a carrier 28 surrounding the shaft 21. The carrier 28 further includes a tubular extension 29 which is coaxial with and spacedly surrounds the shaft 21. The extension 29 has an axially extending through bore 30 for two needle bearings 31, 32 which surround the shaft 21 between the bearings 22 and 23. The carrier 28 is rigidly connected with a gear 33 which meshes with the lower gear 18 on the output shaft 15.  
  The intermediate gear 20 on the shaft 19 meshes with a further gear 35 which is secured to a second carrier 36 telescoped onto the extension 29 of the carrier 28 and rotatable in a friction bearing or sleeve bearing 36 in the housing 10. The tubular intermediate portion 37 of the carrier 36 has at its upper end a transversely extending ring-shaped cover or wall 38 surrounding the adjacent portion of the shaft 21.  
  The upper end portion of the shaft 21 is formed with an axially extending recess or blind bore 39 for a reciprocable selector plunger 40. The lower portion of the plunger 40 is formed with a diametrically extending passage 41 for a sleeve 42 which receives a spherical torque transmitting element 44 and a helical spring 43 tending to move the element 44 radially outwardly. The spring 43 reacts against an end wall 42 of the sleeve 42. The element 44 (hereinafter called ball for short) serves as a means for selectively coupling the shaft 21 with the carrier 28 or 36. To this end, the end wall 38 of the carrier 36 is formed with an axially parallel internal groove 45 which can receive a portion of the ball 44 in one axial position of the selector plunger 40. The upper end portion of the extension 29 of the carrier 28 is rigid with a ring-shaped insert 46 having an axially parallel internal groove 47 which can receive the ball 44 in another axial position of the selector plunger 40. The end wall 42 of the sleeve 42 extends into an axially parallel groove of the shaft 21 so that the plunger 40 can move axially of but cannot rotate relative to the shaft 21.  
  The upper end portion of the plunger 40 extends beyond the bore 39 in the shaft 21 and forms a spool or reel with two flanges 48, 49 surrounding an annular groove 50. As shown in FIG. 3, the groove 50 receives a portion of a shifting pin 52 which is eccentrically mounted in a rotary shank 51 provided with an actuating knob 53. The latter is accessible to the operator at the outer side of the housing 10. Thus, the operator can move the selector plunger 40 axially to thereby introduce the ball 44 into the groove 45 or 47 by rotating the knob 53, preferably with respect to a suitable scale on the housing 10. In that axial position of the plunger 40 which is shown in FIG. 1, the ball 44 extends into the groove 47 so that the shaft 21 can rotate with respect to the carrier 36 and vice versa, but the shaft 21 shares all angular movements of the carrier 28 for the counterweight 27. When the knob 53 is rotated through 180 or less (with respect to the position shown in FIG. 3), the plunger 40 is lifted by the pin 52 and the ball 44 enters the groove 45 so that the shaft 21 must rotate with the carrier 36 but is free to rotate independently of the carrier 28.  
  The eccentric pin 24 at the lower end of the shaft 21 extends into a control device 55 whose setting determines the mode of operation of the sander. The control device 55 has a frame 70 which is fixedly mounted on the platen of the pad 13, and the device 55 can be set to impart to the pad 13 an orbital or a reciprocatory movement. The control device 55 comprises a winged input member 56 which is turnable about a muff 65 and has two projections or wings 57, 58 located diametrically opposite each other. The input member 56 is mounted in a socket 59 provided therefor in a slide or tray 60 having two recesses 61, 62 which are located diametrically opposite each other. In FIG. 2, the common axis 63 of the recesses 61, 62 makes an acute angle with the common symmetry plane 63a of the wings 57, 58. The muff 65 is received in an axial bore of the input member 56 and is rigid with the eccentric pin 24 of the shaft 21. The lower portion of the muff 65 (as viewed in FIG. 1) has a transversely extending bore 66 for a spherical detent member 68 which is biased outwardly by a helical spring 67. The latter urges a portion of the spherical detent member 68 into and beyond a radial aperture 56 of the input member 56 and into an arcuate internal groove 69 of the tray 60. The heretofore described parts of the control device 55 are installed in the substantially square frame 70 which is formed with outwardly bulging portions or sockets 71, 72 respectively adjacent to the recesses 61, 62 of the tray 60. When the projections or wings 57, 58 of the input member 56 assume the positions shown in FIG. 2, their outer edge faces abut against the adjacent portions of the internal surface of the frame 70. If the input member 56 is turned clockwise, as viewed in FIG. 2, so that the common plane 63a of the wings 57, 58 coincides with the common axis 63 of the recesses 61, 62 of the tray 60, the outer edge faces of the wings 57, 58 are spaced apart from the internal surface of the frame 70 and can move into and out of the respective sockets 71, 72.  
  The muff 65 is mounted in an antifriction ball bearing 73 which is mounted in the tray 60. The frame 70 is rigid with the platen of the pad 13. FIG. 2 shows that the length of the tray 60, as considered in the direction from the portion 72 toward the portion 71 of the frame 70, is less than the length of the frame so that the tray 60 can move up and down (as viewed in FIG. 2) when the wings 57, 58 respectively extend into the recesses 61, 62. The width of the tray 60 matches the width of the space which is surrounded by the frame 70.  
  If the winged input member 56 of the control device 55 is moved to the angular position shown in FIG. 2, the sander is set for orbital movement of the pad 13. The knob 53 is assumed to be in the position shown in FIG. 3 so that the plunger 40 assumes its lower end position and the ball 44 extends into the internal groove 47 to thereby couple the shaft 21 to the carrier 28. When the starter switch (not shown) for the motor 11 is closed, the output shaft 15 causes its gears 17, 18 to respectively rotate the gears 35 and 33. The gear 18 is directly in mesh with the gear 33 but the gear 35 receives torque through the medium of the gear 20 so that the gears 33 and 35 rotate in opposite directions. Since the gear 35 does not transmit torque to the shaft 21 (the ball 44 extends into the groove 47 of the carrier 28), the gear 35 merely orbits about the axis of the shaft 21.  
  The gear 18 rotates the shaft 21 by way of the gear 33, carrier 28, ball 44 and sleeve 42. The eccentric pin 24 causes the control device 55 to impart to the pad 13 an orbital movement. At the same time, the pin 25 of the shaft 21 causes the counterweight 26 to orbit about the shaft 21 in the direction of orbital movement of the counterweight 27. The counterweight 27 is rotated directly by the gear 33 and carrier 28, and the counterweight 26 is rotated by the gear 33 indirectly through the medium of carrier 28, ball 44, sleeve 42, shaft 21 and pin 25. The masses of the counterweights 26, 27 are selected in such a way that they compensate for the imbalance of the orbiting pad 13.  
  If the pad 13 is to perform a reciprocatory movement, the winged input member 56 must be turned so that the plane 63a coincides with the axis 63 of FIG. 2. This is achieved by turning the knob 53 from the position shown in FIG. 3 so that the eccentric pin 52 shifts the plunger 40 axially (upwardly, as viewed in FIGS. 1 or 2) in order to introduce the ball 44 into the groove 47 of the wall 38. The shaft 21 is then rotated by the gear 17 through the medium of the gears 20, 35, carrier 36, ball 44 and sleeve 42. The direction of rotation of the shaft 21 is counter to the direction of rotation when the shaft 21 receives torque from the gears 18 and 33 because the gear is rotated by the gear 17 through the intermediary of the gear 20. The counterweight 26 shares the angular movement of the shaft 21 because it is connected thereto by the pin 25. In order to achieve an optimum balancing of masses when the pad 13 performs a reciprocatory rather than an orbital movement, the counterweights 26 and 27 should rotate in opposite directions. This occurs as soon as the plunger is lifted because the direction of rotation of the shaft 21 and counterweight 26 is then changed but the counterweight 27 continues to rotate in the same direction as before because its carrier 28 receives torque from the gears 18 and 33, i.e., the same as when the shaft 21 is driven by the carrier 28. The counterweights 26, 27 bypass each other along both longitudinal sides of the pad 13 and are located diametrically opposite each other when moving along the transverse sides of the pad. Thus, the mass of the counterweights 26, 27 balances the mass of the pad 13 while the latter moves lengthwise and the mass of one counterweight balances the mass of the other counterweight when the counterweights travel along the shorter sides of the pad. Such mode of operation insures a highly satisfactory balancing of masses while the pad performs reciprocatory movements.  
 The control device is operated as follows:  
  It is assumed (by looking at the sander from above) that the shaft 21 is driven to rotate in a counterclockwise direction, i.e., counterclockwise as viewed in FIG. 2. The eccentric pin 24 orbits about the axis of the shaft 21, together with the muff 65, whereby the detent ball 68 of FIG. 2 moves against the inclined surface 69a at the lower end of the groove 69 in the tray and is depressed into the bore 66 of the muff so that the latter can rotate in the input member 56. Therefore, the wings 57, 58 remain in the angular positions of FIG. 2 and prevent a reciprocatory movement of the pad 13 while causing the pad to orbit about the axis of the shaft 21 to the extent determined by eccentricity of the pin 24. This takes place while the plunger 40 dwells in the depressed or lower end position of FIGS. 1 or 2. The frame (and hence the pad 13) is orbited by the wings 57, 58 because the input member 56 orbits with the muff 65 and eccentric pin 24.  
  If the direction of rotation of the shaft 21 is thereupon changed by lifting the plunger 40 in response to rotation of the knob 53, the shaft 21 rotates in a clockwise direction, as viewed in FIG. 2, and the parts 24, 65 orbit clockwise. The spring 67 expels the ball 68 into the groove 69 so that a portion of the ball 68 extends into and beyond the aperture 56. Consequently, as the shaft 21 rotates clockwise, the muff 65 turns the input member 56 clockwise so that the wings 57, 58 respectively enter the recesses 61 and 62 of the tray 60. The wings 57, 58 come to rest when they respectively abut against the surfaces 61a, 62a of the tray 60, i.e, when the axis 63 is located in the plane 63a. As the muff 65 continues to orbit, the surface 69b at the upper end of the groove 69 (as viewed in FIG. 2) depresses the ball 68 into the bore 66 so that the muff 65 is free to turn clockwise in the input member 56 but the wings 57, 58 remain in abutment with the surfaces 61a, 62a. The wings 57, 58 can enter the adjacent portions of the frame 70 in certain angular positions of the eccentric pin 24 with respect to the axis of the shaft 21 (which rotates clockwise). The tray 60 is then free to move in the frame 70 so that the frame 70 merely shares those movements of the tray 60 which cause the pad 13 to move lengthwise. Consequently, the pad 13 reciprocates whenever the shaft 21 is rotated clockwise.  
  The reference characters denote the customary retainers for a sandpaper or a sanding sheet which is to be draped around the cushion of the pad 13 before the power tool is put to use.  
  Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalent of the claims.  
  What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:  
  1. In a pad sander, a combination comprising a housing; a pad movably coupled to said housing; drive means including a prime mover, an eccentric receiving motion from said prime mover and arranged to move said pad with respect to said housing, and control means operable to respectively convert the movement of said eccentric into orbital or reciprocatory movements of said pad; a pair of counterweights rotatable about a common axis to compensate for the imbalance of said pad while the pad performs said movements; and means for respectively rotating said counterweights in the same direction and in opposite directions when said pad respectively orbits and reciprocates with respect to said housing.  
  2. A combination as defined in claim 1, further comprising mechanical selector means for operating said control means.  
  3. A combination as defined in claim 1, wherein said prime mover comprises a rotory output member and further comprising a shaft rotatable in said housing about said common axis, said counterweights being mounted on said shaft and said drive means further comprising gears for rotating said shaft in response to rotation of said output member.  
  4. A combination as defined in claim 3, further comprising a carrier for one of said counterweights, one of said gears being rigid with said carrier.  
  5. A combination as defined in claim 3, further comprising means for transmitting torque from said shaft directly to one of said counterweights.  
  6. A combination as defined in claim 3, wherein said output member is parallel with said shaft and further comprising a carrier rigid with one of said counterweights and mounted on said shaft, said drive means further comprising an intermediate shaft and said gears including first and second gears rigid with said output member, a third gear mounted on said intermediate shaft and meshing with said first gear, a fourth gear rigid with said carrier and meshing with said second gear, and a fifth gear mounted on said first mentioned shaft and meshing with said third gear, said drive means further comprising coupling means operable to transmit torque or to interrupt the transmission of torque from said fifth gear to said first mentioned shaft.  
  7. A combination as defined in claim 6, wherein one of said first and second gears is larger than the other of said first and second gears.  
  8. A combination as defined in claim 6, wherein said eccentric is provided on said first mentioned shaft.  
  9. A combination as defined in claim 6, further comprising a second carrier rigid with said fifth gear, said coupling means being operable to transmit torque or to interrupt the transmission of torque from said second carrier to said first mentioned shaft.  
  10. A combination as defined in claim 9, wherein said coupling means comprises an element which transmits torque from said first mentioned carrier to said first mentioned shaft when said coupling means interrupts the transmission of torque from said second carrier to said first mentioned shaft, and vice versa.  
  11. A combination as defined in claim 10, wherein said element of said coupling means is a spring-biased ball.  
  12. A combination as defined in claim 9, further comprising selector means for operating said coupling means, said first mentioned shaft having an axial bore and said selector means comprising a plunger supporting said element and non-rotatably received in said bore, said plunger being movable axially of said first mentioned shaft between first and second positions in which said element respectively couples said first mentioned shaft to said first mentioned carrier and to said second carrier.  
  13. A combination as defined in claim 12, further comprising means for moving said plunger, including an eccentric coupled to said plunger and actuating means for moving said eccentric.  
  14. A combination as defined in claim 3, further comprising a carrier for one of said counterweights, said carrier having a dished first portion coaxial with and surrounding said shaft and a tubular second portion also coaxial with and surrounding said shaft, said one counterweight being provided at the periphery of said first portion and one of said gears being rigid with one portion of said carrier.  
  15. A combination as defined in claim 14, further comprising antifriction bearings interposed between said shaft and said tubular second portion of said carrier.  
  16. A combination as defined in claim 14, further comprising a second carrier having a tubular portion coaxial with and surrounding said tubular second portion of said first carrier, another of said gears being rigid with the tubular portion of said second carrier.  
  17. A combination as defined in claim 1, wherein said control means comprises a slide for moving said pad and an input member operable by said eccentric to move said slide during each stage of movement of said eccentric to thereby orbit said pad or to move said slide during selected stages of movement of said eccentric to thereby reciprocate said pad.  
  18. A combination as defined in claim 17, wherein said control means further comprises a muff fixed to said eccentric and detent means installed between said input member and said slide and arranged to operate said input member.  
  19. A combination as defined in claim 17, wherein said control means further comprises a frame rigid with said pad and confining said slide, said frame having two sockets and said input member having two projections which move into and from said sockets while said pad reciprocates with respect to said housing.  
  20. A combination as defined in claim 19, wherein said input member is turnable with respect to said slide to move said projections into and from alignment with said sockets, said slide having recesses for said projections.