DYNAMIC MASS BALANCER FOR A ROTATING POWER TOOL

Abstract

The present invention provides, in one aspect, a rotating power tool including a housing, a drive unit within the housing having an electric motor defining a rotational axis, and a drive shaft coupled to the electric motor to receive torque therefrom configured to rotate about the rotational axis, the drive shaft having an eccentric portion. The drive unit further includes an accessory tool configured to orbit about the rotational axis in response to rotation of the eccentric portion of the drive shaft, the accessory tool defining a rotational imbalance. The rotating power tool further includes a dynamic mass balancing system including an actively adjustable counterbalance mass to attenuate vibration caused by the rotational imbalance.

Claims

1. An orbital sander comprising: a housing; a drive unit within the housing, the drive unit including an electric motor defining a rotational axis, and a drive shaft coupled to the electric motor to receive torque therefrom, the drive shaft rotatable about the rotational axis and having an eccentric portion; an accessory tool configured to orbit about the rotational axis in response to rotation of the eccentric portion of the drive shaft, the accessory tool defining a rotational imbalance; and a dynamic mass balancer system including an actively adjustable counterbalance mass to attenuate vibration caused by the rotational imbalance.

2. The orbital sander of claim 1, further comprising: a battery pack coupled to the housing for providing power to the electric motor; and a carrier coupled to the eccentric portion of the drive shaft for orbital motion about the rotational axis.

3. The orbital sander of claim 2, wherein the counterbalance mass is a first counterbalance mass located on a first end of the drive shaft within the carrier.

4. The orbital sander of claim 3, wherein the dynamic mass balancer system further comprises a second counterbalance mass located on a second end of the drive shaft opposite the first end.

5. The orbital sander of claim 1, wherein the dynamic mass balancer system includes an annular dynamic mass balancer.

6. The orbital sander of claim 5, wherein the annular dynamic mass balancer includes an annular main body having one or more moving elements comprising the first counterbalance mass are disposed therein.

7. The orbital sander of claim 6, wherein the one or more moving elements include one or more balls, one or more cylindrical rollers, one or more sliding arcs, or a combination thereof.

8. The orbital sander of claim 1, wherein the dynamic mass balancer includes a pendulum shaped mass balancer.

9. The orbital sander of claim 8, wherein the pendulum shaped mass balancer includes a mounting portion, a swinging mass suspended from the mounting portion that comprises the first counterbalance mass, and a bearing between the mounting portion and the drive shaft.

10. An orbital sander comprising: a housing; a drive unit within the housing, the drive unit including an electric motor defining a rotational axis, and a drive shaft coupled to the electric motor to receive torque therefrom, the drive shaft rotatable about the rotational axis and having an eccentric portion; an accessory tool configured to orbit about the rotational axis in response to rotation of the eccentric portion of the drive shaft, the accessory tool defining a rotational imbalance; and a dynamic mass balancer system including an actively adjustable counterbalance mass to attenuate vibration caused by the rotational imbalance, wherein the dynamic mass balancer system includes a first counterbalance mass located on a first end of the drive shaft within the carrier.

11. The orbital sander of claim 10, wherein the dynamic mass balancer system further comprises a second counterbalance mass located on an opposite, second end of the drive shaft.

12. The orbital sander of claim 10, wherein the dynamic mass balancer system includes an annular dynamic mass balancer having an annular main body in which one or more moving elements comprising the first counterbalance mass are disposed therein.

13. The orbital sander of claim 11, wherein the one or more moving elements include one or more balls, one or more cylindrical rollers, one or more sliding arcs, or a combination thereof.

14. The orbital sander of claim 10, wherein the dynamic mass balancer system includes a pendulum shaped mass balancer having a mounting portion, a swinging mass suspended from the mounting portion that comprises the first counterbalance mass, and a bearing between the mounting portion and the drive shaft.

15. The orbital sander of claim 10, further comprising a plurality of compliant mounts disposed between the motor and the housing.

16. The orbital sander of claim 15, wherein the compliant mounts permit the motor to move relative to the housing as the dynamic mass balancer system counterbalances vibration of the orbital sander during use.

17. An orbital sander comprising: a housing; a drive unit within the housing, the drive unit including an electric motor defining a rotational axis, and a drive shaft coupled to the electric motor to receive torque therefrom, the drive shaft rotatable about the rotational axis and having an eccentric portion; an accessory tool configured to orbit about the rotational axis in response to rotation of the eccentric portion of the drive shaft, the accessory tool defining a rotational imbalance; and a dynamic mass balancer system including an actively adjustable counterbalance mass to attenuate vibration caused by the rotational imbalance, wherein the dynamic mass balancer system includes a first counterbalance mass located on a first end of the drive shaft within the carrier and a second counterbalance mass located on an opposite, second end of the drive shaft.

18. The orbital sander of claim 17, further comprising a plurality of compliant mounts disposed between the motor and the housing.

19. The orbital sander of claim 18, wherein the compliant mounts permit the motor to move relative to the housing as the dynamic mass balancer system counterbalances vibration of the orbital sander during use.

20. The orbital sander of claim 17, wherein the dynamic mass balancer system includes an annular dynamic mass balancer, a pendulum shaped mass balancer, or a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a side view of a rotating power tool in accordance with an embodiment of the invention.

[0009] FIG. 2 is side, cross-sectional view of the rotating power tool of FIG. 1.

[0010] FIG. 3A is front schematic view of a mass balancing system for use with the rotating power tool of FIG. 1.

[0011] FIG. 3B is a schematic view of a component for use with another embodiment of the mass balancing system of FIG. 3A.

[0012] FIG. 3C is a schematic view of a component for use with another embodiment of the mass balancing system of FIG. 3A.

[0013] FIG. 3D is a schematic view of a component for use with another embodiment of the mass balancing system of FIG. 3A.

[0014] FIG. 3E is a schematic view of a component for use with another embodiment of the mass balancing system of FIG. 3A.

[0015] FIG. 3F is a side, perspective view of a portion of a rotating power tool in accordance with another embodiment of the invention.

[0016] FIG. 4A is a schematic view of a dynamic mass balancing system according to an embodiment of the invention, illustrating an unbalanced system.

[0017] FIG. 4B is a schematic view of the dynamic mass balancing system of FIG. 4A, illustrating a balanced system.

[0018] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION

[0019] FIGS. 1 and 2 illustrate a rotating power tool 10 including a main housing 14 having a motor housing portion 18 for supporting a drive unit 50, which includes an electric motor 58 defining a rotational axis 62 and a drive shaft 68 that receives torque from the motor 58, causing the drive shaft 68 to rotate about the axis 62. In the illustrated embodiment of the drive unit 50, a portion of the drive shaft 68 is coupled for co-rotation with a rotor of the electric motor 58, thereby also doubling as a motor output shaft. However, in some embodiments of the drive unit 50, the electric motor 58 may include a separate output shaft for providing torque to the drive shaft 68, with or without an intermediate gear train.

[0020] The main housing 14 further includes a handle portion 16 extending from the motor housing 18 that is graspable by the user of the sander 10 during use. The handle portion 16 includes a controller (e.g., a printed circuit board having one or more microprocessors and multiple field-effect transducers for driving the motor), a battery receptacle 22 for selectively receiving a battery pack 26 to electrically power the electric motor 58 and the controller, when activated. A trigger switch 32 is electrically connected to the controller for providing an input signal to the controller to activate and deactivate the motor 58 in response to actuation of the trigger switch 32. And, a trigger 30 protrudes from the handle portion 16 that is depressible by the user to actuate the trigger switch 32.

[0021] With continued reference to FIG. 2, the drive unit 50 further includes an internal motor housing 19 located within an interior portion of the motor housing 18 for supporting a first bearing 72, which supports a first portion of the drive shaft 68, and a second bearing 75, which supports an opposite, second portion of the drive shaft 68. The drive unit 50 also includes an eccentric bushing 71 mounted on the drive shaft 68 for co-rotation therewith and a radial bearing 74 mounted on the exterior of the bushing 71. An eccentric carrier 66 is mounted to an outer race of the bearing 74. The eccentric carrier 66 is configured to be axially supported in the housing 18 by a shoulder portion 69 surrounding the eccentric bearing 74 and a retaining ring 73 located opposite shoulder 69. The carrier 66 is configured to receive a plurality of fasteners 78 (e.g., screws) to fasten a pad attachment 82 to the eccentric carrier 66.

[0022] The eccentric carrier 66 further includes a cylindrical bore 67 for receiving the pad attachment 82. The bore 67 not only helps to control the concentric alignment of the pad attachment 82 and the carrier 66, but also reduces the overall length of the sander 10, which can be advantageous for when the user is trying to operate the sander 10 in confined spaces. The pad attachment 82 is configured to selectively retain an accessory tool, such as a sanding pad 100. The sanding pad 100 includes a main body 116 having a bottom surface 120 to which a sanding sheet is attached for performing a sanding operation, and a connection portion 114 extending upward from the main body 116 in an opposite direction as the lower surface 120. The connection portion 114 includes a locking geometry 110 configured to engage the pad attachment 82 to axially affix the sanding pad 100 to the pad attachment 82 for orbital motion therewith.

[0023] The rotating power tool 10 further includes a plurality of clamps 34 (FIG. 1) secured on opposite sides of the motor housing portion 18 by fasteners 36 to obtain a flush profile with the exterior of the motor housing 18. The clamps 34 are configured to impart a clamping force onto a portion of the drive unit 50. Specifically, the fasteners 36 extend through the motor housing 18 to connect two housing clamshells that make up the housing 14 of the sander 10. This relationship imparts a clamping force onto the first bearing 72 to clamp the bearing 72 between the two housing clamshells. In addition, the clamps 34 are configured to retain a first end 39 of a torque absorber 38 on the motor housing 18. The torque absorber 38 is configured to flex and absorb the torque from the motor 58 to prevent the eccentric carrier 66 from free rotation about the rotational axis 62. The torque absorber 38 further includes a second end 41 mounted to the carrier 66 for limiting the movement of the carrier 66 to orbital motion about the rotational axis 62 in response to rotation of the drive shaft 68.

[0024] With respect to FIGS. 1, 2, and 4A-4B, to rotationally balance the rotating power tool 10 during use, the sander 10 includes a dynamic mass balancing system including a front mass balancing system 200, a rear mass balancing system 300, and a plurality of compliant mounts 124. The compliant mounts 124 (e.g., rubber isolators) are configured to suspend the motor 58 within the housing 18 via the internal motor housing 19 in order to permit the motor 18 to move relative to the motor housing 18 such that the systems 200, 300 can provide a counterbalance to the vibration of the tool 10 during use. The front mass balancing system 200 is located within the eccentric carrier 66 on a lower portion 70 of the drive shaft 68 and the rear mass balancing system 300 is located rearward of the motor 58 on an upper portion of the drive shaft 68. Both the front and rear mass balancing systems 200, 300 include a dynamic mass balancer.

[0025] With respect to FIGS. 4A-4B, the purpose of the dynamic mass balancer is to automatically counteract any rotating imbalances 216 inherent in the sanding pad 100 or any other orbiting accessory attached to the pad attachment 82. For example, FIG. 4A illustrates a system where the dynamic mass balancer is configured as a ball balancer 202 including an annular main body 204 and a plurality of balls 208 retained within the main body 204 that, when combined, define a counterbalance mass capable of offsetting any rotational imbalances in the system. In this system, the imbalance 216 is eccentrically orbiting about the rotational axis 62 on an eccentric axis 63, while the suspended mass (i.e., an accessory tool) is orbiting about the rotational axis 62 along an eccentric travel path 212. In the example illustrated in FIG. 4A, the imbalance 216 is in-line with the balls 208 such that both the center of gravity of the imbalance 216 and the counterbalance mass of the balls 208 are on the same side of the system. This configuration creates a heavy side out condition where the dynamic mass balancer hasn't properly oriented the counterbalance mass to eliminate the vibration caused by the imbalance 216.

[0026] Alternatively, FIG. 4B illustrates a light side out condition where the counterbalance mass of the balls 208 is oriented opposite of the center of gravity of the imbalance 216. In this condition, the counterbalance mass of the balls 208 eliminates the vibration caused by the eccentrically rotating imbalance 216. With the presence of an imbalance 216 in the system, the counterbalance mass will move to a position that directly counteracts the eccentric movement of the imbalance 216 until the vibration caused by the imbalance 216 is effectively neutralized.

[0027] With respect to FIGS. 3A-3F, the dynamic mass balancer can be configured as an annular system (such as the ball balancer 202) or a pendulum-shaped system. FIGS. 3A-3C illustrate different embodiments of annular systems. For example, with reference to FIG. 3B and FIG. 3C, the balls 202 can be replaced with cylindrical rolling elements 220 or sliding arc-shaped elements 224, respectively, to form the counterbalance mass. In these embodiments, the cylindrical rolling or sliding arc-shaped elements 220, 224 move within the annular main body 204 about the rotational axis 62 to counteract the eccentric movement of the imbalance 216. It is important to reduce the friction in the system, but not so much so that the counterbalance mass is precluded from moving within the main body 204 as the tool 10 is operated. Essentially, when the sander 10 begins to rotate, the coefficient of friction between the counterbalance mass (i.e., balls, cylindrical rolling elements, or sliding arc-shaped elements) and the main body 204 is sufficiently low to allow the counterbalance mass to rotate within the main body 204 about the rotational axis 62 to counteract the imbalance 216. If the coefficient of friction is too high between the counterbalance mass and the main body 204, this could create dead zones, or regions where the counterbalance mass could get trapped and not rotate about the rotational axis 62. If the counterbalance mass remains in the dead zone, the sander 10 can become unbalanced and emit a relatively high magnitude of vibration to the user.

[0028] FIGS. 3D-3F illustrate alternative embodiments of a pendulum-shaped mass balancer. The pendulum balancer includes a mounting portion 228, a swinging mass 232 suspended from the mounting portion 228, and a bearing 236 (e.g., ball bearing, sleeve bearing, etc.) positioned between the drive shaft 68 and the mounting portion 228 for frictionally engaging the drive shaft 68. Similar to the annular balancers, the bearing 236 needs to provide sufficiently low friction between the shaft 68 and the bearing 236 to allow the pendulum balancers to rotate, but not too much to create any dead zones where the pendulum balancers could otherwise seize on the drive shaft 68. To achieve a desired counterbalance mass, the user can stack multiple pendulum balancers (e.g., four or more as shown in FIG. 3F) on the drive shaft 68 so that the pendulums are spaced about 3-4 mm apart. Similar to the annular systems, the pendulum balancers rotate about the rotational axis 62 until the counterbalance mass, formed by a combination of the respective pendulum balancers, automatically adjusts to eliminate the vibration from the imbalance 216.

[0029] In some embodiments of the sander 10, the dynamic mass balancing system can incorporate both a pendulum-shaped mass balancer and an annular-shaped mass balancer for eliminating the vibration of the rotating unbalance 216.

[0030] With respect to FIGS. 1, 2, and 3A-3F, the front and rear mass balancing systems 200, 300 of the sander 10 can incorporate either an annular dynamic mass balancer, a pendulum-shaped mass balancer, or a combination of both. In the illustrated embodiment, the front mass balancing system 200 includes a plurality of pendulum balancers 232 arranged on a lower portion of the drive shaft 68. Each of the pendulum balancers 232 includes a bearing 236 for imparting a sufficient amount of friction between the drive shaft 68 and the respective pendulum balancers 232 to permit the pendulum balancers 232 to move about the rotational axis 62 such that the pendulum balancers 232 can properly and automatically adjust to counteract the vibration created by the imbalance 216. Similarly, the rear balancing system 300 includes a plurality of pendulum balancers 232 supported on an upper portion of the drive shaft 68 via respective bearings 236. The rear balancing system 300 further includes a ball balancer 202 surrounding one of the pendulum balancers 232 for providing additional counterbalance mass. In other embodiments of the rear balancing system 300, the ball balancer 202 could be replaced with any of the other annular mass balancers (e.g., cylindrical/sliding arc-shaped rolling elements).

[0031] In other embodiments of the sander 10, the front and rear mass balancing systems 200, 300 could be positioned anywhere along the drive shaft 68 to counteract the vibration created by the imbalance 216.

[0032] By incorporating the dynamic mass balancing system into the sander 10, the user is permitted to use a wider variety of attachments (e.g., multi-tool attachments or sander attachments) as compared to other conventional rotating power tools. This is due to the front and rear mass balancing systems 200, 300 being comprised of multiple mass balancing systems (e.g., pendulum or annular systems), which allow for a greater range of possible rotating imbalances 216 that can be neutralized by the systems 200, 300. Because each of the systems 200, 300 utilize multiple members 202, 232 to form the counterbalance mass to counteract the imbalance 216, one or more of these members 232, 202 can be adjusted as needed to eliminate the vibration caused by the imbalance 216. Furthermore, the dynamic mass balancing system allows the user to alter the eccentricity of the sanding pad 100 by re-orienting the systems 200, 300 along the drive shaft 68.

[0033] The various masses in any of the balancing systems described above will shift opposite a rotating imbalance above the first natural frequency of a suspended system under the influence of the body forces created from the motion of the suspended system from the rotating imbalance. As the mass(es) move opposite the suspended system, the system becomes balanced, the body forces are decreased or eliminated, and the mass(es) stop moving opposite the imbalance, reaching an equilibrium rotating condition with little or no vibration. The balancing systems described above exploit this behavior with two such balancers on opposite ends of a rotating motor/bearing suspended system, automatically in real time adjusting the dynamic masses during operation to reduce vibration.

[0034] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.

[0035] Various features of the invention are set forth in the following claims.