Eccentric stroke adjusting mechanism

The present invention relates to an eccentric stroke adjusting mechanism for use in a power tool with a principle drive shaft comprising a first and a second eccentric member mounted on the principle drive shaft respectively and a coupling member for connecting the first and the second eccentric member. The principle drive shaft has a central axis. The first eccentric member has a first central axis and the second eccentric member has a second central axis. The eccentric stroke of the first central axis and the second central axis with respect to a central axis of the principle drive shaft is adjustable. The eccentric stroke adjusting mechanism of the invention is reliable and the adjusted eccentricity is non-displaceable. The eccentric stroke adjusting mechanism can be applied to adjust the eccentric stroke of single disk or multiple (e.g., double) disks.

BACKGROUND

1. Field of the Invention

The present invention relates to an eccentric stroke adjusting mechanism for use in a power tool and to a power tool per se.

2. Background Art

As illustrated in U.S. Pat. No. 4,744,177 and EP-A-0820838, known abrasive power tools such as sanders and grinders generally comprise a housing, a motor vertically located inside the housing, a principle drive shaft, a working (sanding) plate and an eccentric stroke adjusting mechanism. The eccentric stroke adjusting mechanism is used to adjust the vibration amplitude of the working (sanding) plate to meet different requirements of different workpieces. The eccentric stroke adjusting mechanism comprises an eccentric shaft securely attached to the principle drive shaft, an eccentric driving device and a bearing for connecting the eccentric driving device and the working (sanding) plate. However such an eccentric stroke adjusting mechanism is not easily and reliably balanced and the adjusted eccentricity is easy to displace. Furthermore the eccentric stroke adjusting mechanism can only be applied to adjust single disk working (sanding) plate.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a reliable and widely applicable eccentric stroke adjusting mechanism.

In an embodiment, the present invention provides an eccentric stroke adjusting mechanism for use in a power tool with a principle drive shaft. The eccentric stroke adjusting mechanism may comprise a first and a second eccentric member mounted on the principle drive shaft and a coupling member for coupling the first and the second eccentric members. The first eccentric member may have a first central axis and the second eccentric member may have a second central axis. The eccentricity of the first central axis and the second central axis with respect to a central axis of the principle drive shaft is adjustable.

The eccentric stroke adjusting mechanism of the invention advantageously prevents adjusted eccentricity from being easily displaced and is more reliable. More particularly, the relationship and co-action between the first eccentric member, the second eccentric member and the coupling member prevents the adjusted eccentricity from displacement. The eccentric stroke adjusting mechanism can be applied to adjust the eccentric stroke of a single disk or multiple (e.g., double) disks.

Viewed from a first aspect, the present invention provides an eccentric stroke adjusting mechanism for use in a power tool, the eccentric stroke adjusting mechanism comprising:a principle drive shaft with a central axis;a first eccentric member mounted radially on the principle drive shaft, the first eccentric member having a first central axis;a second eccentric member mounted radially on the principle drive shaft, the second eccentric member having a second central axis; anda coupling member for coupling the first eccentric member to the second eccentric member, wherein the eccentricity of the first central axis and the eccentricity of the second central axis with respect to the central axis of the principle drive shaft are adjustable.

In a preferred embodiment, the first eccentric member has a first eccentric sleeve and the second eccentric member has a second eccentric sleeve. The first eccentric sleeve of the first eccentric member and the second eccentric sleeve of the second eccentric member are rotatable relative to the principle drive shaft, wherein a central axis of the first eccentric sleeve is the first central axis of the first eccentric member and a central axis of the second eccentric sleeve is the second central axis of the second eccentric member.

Particularly, the first eccentric member preferably has a first eccentric shaft, the second eccentric member has a second eccentric shaft and the first eccentric shaft and second eccentric shaft are securely mounted radially on the principle drive shaft, wherein the first eccentric sleeve and the second eccentric sleeve are rotatably mounted on the first eccentric shaft and the second eccentric shaft respectively, wherein a central axis of the first eccentric shaft and a central axis of the second eccentric shaft are eccentric with respect to the central axis of the principle drive shaft, wherein the central axis of the first eccentric sleeve is eccentric with respect to the central axis of the first eccentric shaft and to the central axis of the principle drive shaft and wherein the central axis of the second eccentric sleeve is eccentric with respect to the central axis of the second eccentric shaft and to the central axis of the principle drive shaft.

A first sanding plate may be operably connected or coupled to the first eccentric sleeve so that in practice the central axis of the first eccentric sleeve is the central axis of the first eccentric member and of the first sanding plate. Similarly a second sanding plate may be operably connected or coupled to the second eccentric sleeve so that in practice the central axis of the second eccentric sleeve is the central axis of the second eccentric member and of the second sanding plate.

Preferably, the central axis of the first eccentric sleeve and the central axis of the second eccentric sleeve are on opposite sides of the central axis of the principle drive shaft. The central axis of the first eccentric sleeve and the central axis of the second eccentric sleeve may be parallel to the central axis of the principle drive shaft. The central axis of the first eccentric sleeve, the central axis of the second eccentric sleeve and the central axis of the principle drive shaft may be in a common plane. The central axis of the first eccentric sleeve and the central axis of the second eccentric sleeve may be equidistant from the central axis of the principle drive shaft. The central axis of the first eccentric sleeve and the central axis of the second eccentric sleeve may be angularly displaced relative to the central axis of the principle drive shaft by 180°.

Preferably, the central axis of the first eccentric shaft and the central axis of the second eccentric shaft are on opposite sides of the central axis of the principle drive shaft. The central axis of the first eccentric shaft and the central axis of the second eccentric shaft may be parallel to the central axis of the principle drive shaft. The central axis of the first eccentric shaft, the central axis of the second eccentric shaft and the central axis of the principle drive shaft may be in a common plane. The central axis of the first eccentric shaft and the central axis of the second eccentric shaft may be equidistant from the central axis of the principle drive shaft. The central axis of the first eccentric shaft and the central axis of the second eccentric shaft may be angularly displaced relative to the central axis of the principle drive shaft by 180°.

In an embodiment, the first eccentric sleeve and second eccentric sleeve may be substantially cylindrical and may terminate in a radial collar.

A bearing may be tightly mounted radially on the second eccentric sleeve. A bearing seat may be mounted around the perimeter of the bearing. A sanding plate may be fastened to the bearing seat.

Preferably, the coupling member is securely mounted on the first eccentric shaft and has a first pin on an upper surface and a second pin on a lower surface, wherein each of the first eccentric sleeve and the second eccentric sleeve has a radial slot to receive the first pin and second pin respectively, wherein the width of the slot approximates to the diameter of the pin. To mount the coupling member on the first eccentric shaft, the first eccentric shaft may comprise an annular protrusion on its lower face.

The coupling member preferably has an operating body rotatably mounted on the principle drive shaft and an extension pin extending axially from the operating body, wherein each of the first eccentric sleeve and the second eccentric sleeve has a receiving bore for receiving the extension pin, wherein the diameter of the receiving bore approximates to the diameter of the extension pin and the receiving bore is longer than the extension pin.

Preferably, a plurality of locating sockets are formed on the outer surface of the first eccentric shaft and of the second eccentric shaft and a plurality of receiving recesses are formed on the inner circumferential surface of the first eccentric sleeve and of the second eccentric sleeve, wherein in each receiving recess is seated an elastic element (e.g., a spring) connected to a locating post, wherein each locating post is selectively received in a locating socket so as to restrainedly couple the first and the second eccentric sleeve with the first and the second eccentric shaft respectively.

Viewed from a further aspect, the present invention provides a power tool comprising:a housing;a rotary motor in the housing; andan eccentric stroke adjusting mechanism as hereinbefore defined.

Preferably, the power tool further comprises a first sanding plate connected or coupled to the first eccentric member. The power tool may further comprise a second sanding plate connected or coupled to the second eccentric member.

The first sanding plate and second sanding plate may terminate at the base of housing. The first sanding plate and second sanding plate may be an outer sanding and an inner sanding plate. The or each sanding plate may be annular (e.g., stepped annular).

Preferably, the power tool further comprises a principle drive shaft locking device. In an embodiment, the principle drive shaft locking device may comprise:a chuck mounted radially on the principle drive shaft, wherein the chuck has a skirt extending axially downwardly from its circumferential edge, wherein a plurality of recesses are located around the skirt; anda locking member attached to the housing, wherein the locking member is selectively insertable into a recess to lock the chuck and prevent the principle drive shaft from rotating.
More preferably, the power tool may comprise: a balancing drum, wherein the chuck has a central aperture surrounded by an eccentric hub and the balancing drum is securely mounted on the eccentric hub.

A plurality of spaced apart location holes may be formed around the eccentric hub. The balancing drum may comprise a central aperture bound by a hub.

In an embodiment of the present invention, the power tool further comprises:a clutch securely mounted radially on the first eccentric member (e.g., the first eccentric sleeve), wherein the clutch comprises an annular main body, wherein the annular main body has an inner circumferential surface with a plurality of first truncated conical recesses formed thereon and an outer circumferential surface with a plurality of second truncated conical recesses formed thereon, wherein in each first truncated conical recess and second truncated conical recess is seated an elastic element (e.g., a spring) connected to a roller whereby the elastic element urges the roller outwardly, wherein when in use the principle drive shaft rotates the rollers in the inner circumferential surface of the clutch securely engage the principle drive shaft and the rollers in the outer circumferential surface of the clutch disengage the first sanding plate.

The annular main body may abut an end face of the balancing drum (e.g., the hub). The balancing drum may have a part radial recess extending from the hub. A spring and a ball head locating post connected to the spring may be disposed in the recess. The ball head locating post may be urged partly into a location hole on the eccentric hub to restrainedly couple the balancing drum and the chuck.

The annular main body may abut an end face of the chuck (e,g, the eccentric hub). The annular main body may have a radial recess. A spring and a ball head locating post connected to the spring may be disposed in the recess. The ball head locating post may be urged partly into a location hole on the eccentric hub to restrainedly couple the clutch and the chuck.

In the base of each truncated conical recess, there may be a narrow receiving bore. The elastic element may be received in the receiving bore. An axial projection may extend from the lower face of the annular main body. The axial projection may engage a recess in the upper end of the first eccentric sleeve to securely connect the clutch and the first eccentric sleeve.

Preferably, the principle drive shaft is locked by the principle drive shaft locking device to adjust the eccentric stroke of the sanding plate, the first sanding plate securely engages the rollers seated in the outer circumferential surface of the clutch and the rollers seated in the inner circumferential surface of the clutch disengage the principle drive shaft. Particularly preferably the power tool further comprises: an outer race mounted radially on the annular main body between the clutch and the first sanding plate. A sanding plate may be mounted radially on the outer race. A support bearing may be radially mounted on the first eccentric sleeve. The support bearing may be substantially axially aligned with the outer race. The sanding plate may be radially mounted on the outer race and the bearing.

The power tool may further comprise: a balancing block connected or coupled to the second eccentric member.

The present invention will now be described in a non-limitative sense with reference to the accompanying Figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, a first embodiment of the present invention is a rotary sander. The sander comprises generally a housing1, a motor2vertically disposed inside the housing1, a principle drive shaft3, a sanding plate4at the base of the housing and an eccentric stroke adjusting mechanism5.

Referring toFIGS. 2-5, the housing1comprises an upper housing part12and a lower housing part14securely connected to each other. A fan16is securely attached to the principle drive shaft3. The principle drive shaft3comprises an armature shaft30and a connecting shaft32connected to the lower end of the armature shaft30. The connecting shaft32and the armature shaft30have a common axis X0. The connecting shaft32has an irregular cross-section. The sanding plate4has an annular inner plate42and an annular outer plate44. A braking system6is disposed between the lower housing part14and the annular outer plate44.

The eccentric stroke adjusting mechanism5comprises a principle drive shaft locking device8, a first eccentric member56, a second eccentric member58and a coupling member77for coupling the first eccentric member56and the second eccentric member58. The first eccentric member56, the coupling member77and the second eccentric member58are radially mounted on the connecting shaft32in sequence downwardly.

The principle drive shaft locking device8comprises a chuck52mounted radially on an upper part of the connecting shaft32and a bolt member50. The chuck52has a skirt520extending axially downwardly from its circumferential edge. A plurality of recesses524are distributed around the skirt520. The bolt member50is attached to the lower housing part14and can be selectively inserted into a corresponding recess524to lock the chuck52during adjustment of the eccentric stroke of the sanding plate4(as described below). The chuck52has a substantially central aperture51surrounded by an eccentric hub53. A plurality of spaced apart location holes525are formed in the eccentric hub53.

A balancing drum55is mounted on the eccentric hub53so as to cooperate with the annular inner plate42whereby to balance the weight of the annular outer plate44. The balancing drum55comprises a central aperture57abound by a hub57. The balancing drum55has a part radial recess59extending from the hub57. A spring590and a ball head locating post592connected to the spring590are disposed in the recess59. The ball head locating post592extends partially into a location hole525under the force of the spring590to restrainedly couple the balancing drum55and the chuck52.

The rotary sander of the first embodiment of the present invention further comprises an overrun clutch54. The overrun clutch54is a one way rotation clutch with a self-locking function. The overrun clutch54has an annular main body60abutting an end face of the hub57. An outer race64is mounted radially on the annular main body60between the overrun clutch54and the annular outer plate44. A locking ring594is interposed axially between the outer race64and the balancing drum55. The annular main body60has an inner circumferential surface with three first truncated conical recesses662formed thereon and an outer circumferential surface with three second truncated conical recesses66formed thereon. In the base of each of the first truncated conical recess662and second truncated conical recess66is a narrow receiving bore61. A loaded spring68is disposed in each narrow receiving bore61and individually connects to a roller63seated in the conical recess66,662. The loaded spring68urges the roller63away from the narrow receiving bore61. An axial projection602extends from the lower surface of the annular main body60adjacent to the inner circumferential surface.

The first eccentric member56is radially mounted on the principle drive shaft3. The first eccentric member56comprises a first eccentric shaft62having a first bore65formed along an axis parallel to its central axis X3. The shape of the first bore65matches the shape of the connecting shaft32so that the first eccentric shaft62can be securely mounted radially on the connecting shaft32. The central axis X3is eccentric with respect to the central axis X0. On the upper end of the first eccentric shaft62is radially mounted the overrun clutch54. The first eccentric member56further comprises a first eccentric sleeve69which is rotatably mounted on a lower end of the first eccentric shaft62. The first eccentric sleeve69has a central axis X1and the eccentricity of the central axis X1with respect to the central axis X0of the principle drive shaft3is adjustable. The central axis X1is eccentric with respect to the central axis X3.

A support bearing71is tightly mounted on the first eccentric sleeve69and its outer surface is substantially aligned with the outer surface of the outer race64. The annular outer plate44is tightly engaged with the outer surface of the outer race64and of the support bearing71. The central axis of the annular outer plate44is coincident with the central axis X1of the first eccentric sleeve69and so the central axis X1defines in practice the central axis of the first eccentric member56as a whole. A washer70is disposed axially between the annular main body60and the support bearing71. The end of the first eccentric sleeve69abuts the lower face of the washer70and has a recess622formed on its upper end to receive the projection602so that the first eccentric sleeve69is securely connected to the overrun clutch54. The first eccentric shaft62has a plurality of bores67extending parallel to its central axis X3to reduce its weight.

The second eccentric member58is constructed substantially symmetrically to the first eccentric member56with respect to the principle drive shaft3. The second eccentric member58comprises a second eccentric shaft73securely mounted radially on the connecting shaft32and a second eccentric sleeve75rotatably mounted on the second eccentric shaft73. A central axis X4of the second eccentric shaft73and the central axis X3of the first eccentric shaft62are symmetrically distributed around the central axis X0. A central axis X2of the second eccentric sleeve75and the central axis X1of the first eccentric sleeve69are symmetrically distributed around the central axis X0. The central axis X2defines in operation the central axis of the second eccentric member58as a whole.

The coupling member77is mounted on an annular protrusion624formed on the bottom face of the first eccentric shaft62. The coupling member77has a first and second pin79formed respectively on its top surface and bottom surface. The first and second pin79are symmetrically distributed with respect to the central axis of the coupling member77. The first eccentric sleeve69and the second eccentric sleeve75each has a radial slot80to receive a corresponding pin79. The width of the slot80approximates to the diameter of the pin79.

A bearing71is tightly mounted radially on the second eccentric sleeve75. A bearing seat82is mounted around the perimeter of the bearing71. A plurality of bolts fasten the annular inner plate42to the bearing seat82. The annular inner plate42and the second eccentric sleeve75are coaxial. A guard91is mounted on the bottom end of the connecting shaft32to retain the second eccentric member58and a bolt93is fastened tightly thereto.

When the eccentric stroke of the sanding plate4is to be adjusted, the bolt member50is inserted into a corresponding recess524of the chuck52so as to prevent the principle drive shaft3from rotating. The annular outer plate44is rotated in the direction indicated by an arrow a inFIG. 3. The outer race64rotates together with the annular outer plate44. Friction between the outer race64and the roller63of the overrun clutch54causes the first eccentric sleeve69, the second eccentric sleeve75and the annular inner plate42to rotate accordingly. By virtue of the fact that the annular outer plate44is securely coupled to and coaxial with the first eccentric sleeve69, the central axis X1of the annular outer plate44rotates around the central axis X3of the first eccentric shaft62. Since the central axis X0of the principle drive shaft3is fixed, the distance between the central axis X1and X0(i.e., the eccentric stroke of the annular outer plate44) changes. The eccentric stroke of the central axis X2of the annular inner plate42with respect to the central axis X0also changes and approximates to the eccentric stroke of the annular outer plate44. The overrun clutch54, the spring590and the ball head locating post592disposed between the balancing drum55and the chuck52prevent the adjusted eccentric stroke from displacement. According to the requirements of the workpiece, the eccentric stroke adjusting mechanism5can adjust the eccentric stroke of more than one sanding plate42,44at the same time and can ensure that the sander is balanced during operation.

FIG. 6illustrates a rotary sander of a second embodiment of the present invention. The parts in the second embodiment which are the same as or similar to the parts in the first embodiment will not be described in detail and will adopt the same numeral. The rotary sander of the second embodiment comprises an upper housing part12, a lower housing part14, a motor2vertically disposed inside the housing1, a principle drive shaft3, a sanding plate4and an eccentric stroke adjusting mechanism5. The eccentric stroke adjusting mechanism5comprises an overrun clutch54, a first eccentric member56and a second eccentric member58. A coupling member77couples the first eccentric member56and the second eccentric member58. The sanding plate4of the second embodiment is a single disk. A balancing block9is directly attached to a second eccentric sleeve75of the second eccentric member58(in place of the annular inner plate44and the bearing of the first embodiment).

In the second embodiment, no balancing drum55is present. Instead the overrun clutch54engages the chuck52directly and a recess59is present on the upper surface of an annular main body60of the overrun clutch54. A spring590and a ball head locating post592connected to the spring590are disposed in the recess59. The ball head locating post592extends partially into a location hole525under the force of the spring590to restrainedly couple the overrun clutch54and the chuck52.

FIGS. 7-9illustrate an eccentric stroke adjusting mechanism5′ of a third embodiment of the present invention (similar to the eccentric stroke adjusting mechanism5of the first and second embodiment described above) for use in a power tool having a principle drive shaft3′. The eccentric stroke adjusting mechanism5′ comprises a first eccentric member56′ mounted on the principle drive shaft3′, a second eccentric member58′ mounted on the principle drive shaft3′ and a coupling member77′ for coupling the first eccentric member56′ and the second eccentric member58′.

The first eccentric member56′ has a first central axis X1′. The second eccentric member58′ has a second central axis X2′. The eccentric stroke of the first central axis X1′ and the second central axis X2′ with respect to a central axis X0′ of the principle drive shaft3′ is adjustable. The first eccentric member56′ comprises a first eccentric shaft62′ mounted radially on the principle drive shaft3′ and a first eccentric sleeve69′ rotatable with respect to the principle drive shaft3′. The second eccentric member58′ comprises a second eccentric shaft73′ mounted on the principle drive shaft3′ and a second eccentric sleeve75′ rotatable with respect to the principle drive shaft3′. A central axis X3′ of the first eccentric shaft62′ and a central axis X4′ of the second eccentric shaft73′ are eccentric with respect to the central axis X0of the principle drive shaft3′ and on opposite sides thereof. The first eccentric sleeve69′ and the second eccentric sleeve75′ are separately rotatably mounted on the first eccentric shaft62′ and the second eccentric shaft73′. The central axis of the first eccentric sleeve69′ defines in practice the central axis X1′ of the first eccentric member56′. The central axis of the second eccentric sleeve75′ defines in practice the central axis X2′ of the second eccentric member58′. The central axis X1′ of the first eccentric sleeve69′ is eccentric with respect to the central axis X3′ of the first eccentric shaft62′ and the central axis X0′ of the principle drive shaft3′. The central axis X2′ of the second eccentric sleeve75′ is eccentric with respect to the central axis X4′ of the second eccentric shaft73′ and the central axis X0′ of the principle drive shaft3′. The central axes X1′ and X2′ are on opposite sides of the central axis X0′.

A plurality of locating sockets83are formed on the outer surface of the first eccentric shaft62′ and the second eccentric shaft73′. A plurality of radial receiving recesses85are formed on the inner circumferential surface of the first eccentric sleeve69′ and of the second eccentric sleeve75′. The receiving recesses85each have an elastic element87seated therein and a locating post89is connected to the elastic element87. The locating post89can be selectively received in one of the corresponding locating sockets83so as to restrainedly couple the first and the second eccentric sleeve69′,75′ with the first and the second eccentric shaft62′,73′ respectively.

The coupling member77′ has an operating body84rotatably mounted on the principle drive shaft3′ and an extension pin86extending downwardly therefrom. Each of the first and the second eccentric sleeve69′,75′ have an axial receiving bore88to accommodate the extension pin86. The diameter of the receiving bore88approximates to the diameter of the extension pin86. The length of the receiving bore88is longer than the length of the extension pin86.

Sanding plates46and48are coupled to the first eccentric sleeve69′ and the second eccentric sleeve75′ via a bearing90. A seal ring92is interposed between the sanding plate46and the first eccentric sleeve69′.

The operating body84of the coupling member77′ can be manually rotated to allow the eccentric stroke of the sanding plates46and48to be adjusted. The principle of adjustment is the same as described above for the first and the second embodiment.