Power tool

Details Power tool Power tool

2001-06-14

2004-09-14

Wilson, Lee D. (Department: 3723)

Abrading

Frame or mount

Portable abrader

C451S490000, C451S548000

Reexamination Certificate

active

06790134

ABSTRACT:

The present invention relates to a means of driving a power tool and the position of this means within the power tool and in particular a power module and an electric motor for driving a belt sander and the position of the power module and the electric motor in relation to the sandpaper belt of the belt sander.
Sandpaper is used for the removal of surface layers like, for example, a layer of varnish on a piece of wood. A piece of sandpaper may be used manually, which involves the user repeatedly rubbing the sandpaper against the layer of varnish to be removed and the abrasive nature of the sandpaper steadily removing this surface layer. The user will cease the rubbing action once satisfied that the layer of varnish has been removed, thus exposing a clean piece of wood from underneath the varnish.
Manual usage of sandpaper allows the user access to tight corners, however it may also involve a lot of time and significant effort on the part of the user. This time and effort increases with the size of the task and many would agree that the removal of a layer of varnish from the wooden floor of a room in a typical house would be too onerous a task to be attempted by manual use of sandpaper. However, a power tool in the form of an electric sander, using electrical power to drive the rubbing motion of the sandpaper against the surface layer to be removed, would complete such a task more quickly and with significantly less physical effort on the part of the user.
An electric sander uses domestic mains electrical supply or battery electrical supply to drive an electric motor, which in turn drives a mechanism capable of converting the motor's rotational motion into sandpaper rubbing motion. Sandpaper rubbing motion typically takes one of two forms.
Substantially constant flat linear motion moving relative to the stationary surface layer to be removed, as achieved by a continuous sandpaper belt with abrasive surface on the exterior, rotating quickly in the form of a flat loop about a first driven roller and a second non-driven roller, the rollers being parallel to each other.
Vibrating movement within a flat plane thus quickly moving the abrasive side of the flat sandpaper back and forth against the surface layer to be removed.
Electric sanders may embody either of the above methods of sandpaper rubbing motion depending on the manufacturing cost of the electric sander and the scale of its intended purpose. When designing an electric sander consideration must also be paid to its shape, size and ergonomics. The shape of the electric sander's body in relation to its sanding surface will influence the electric sander's ability to reach edges and tight corners, something which is not a consideration when manually using sandpaper. An electric sander employing the rubbing motion as described in (a) above is called a belt sander.
A conventional belt sander typically comprises a main body element having a handle with an electrical switch and containing an electric motor, a driving mechanism, a driven roller, a non-driven roller, and a sandpaper belt, the sandpaper belt being located on the underside of the body element and held in a flat loop by the two rollers. The rollers are connected to the body element and the driven roller is rotatably driven by the electric motor via the driving mechanism, and both the electric motor and driving mechanism are located within or attached to the body element. Some electric motors, like for example a universal motor, may be powered by a domestic mains electrical supply or battery electrical supply. Other electric motors require a power module to convert a domestic mains electrical supply or battery electrical supply into a more suitable electrical supply. The choice of motor and hence the requirement of a power module depends on the desired performance of the belt sander. If a power module is required, it is normally located in the body element of a conventional belt sander and may be powered by domestic mains electrical supply or battery electrical supply.
Typically a conventional belt sander transfers the rotational motion of the electric motor to the driven roller via a driving mechanism comprising a toothed belt and two toothed wheels, arranged in the form of a pulley system. The first toothed wheel is attached to, and rotated by, the electric motor, thereby turning the toothed belt. The toothed belt passes by the side of the sandpaper belt and turns the second toothed wheel which is attached to and rotates the driven roller. This transfer of rotational motion from the electric motor to the driven roller urges the sandpaper belt to turn about the two rollers in the shape of a flat loop, the flat lower exterior face of the sandpaper acting as an abrasive wall against the work surface.
The operation of a belt sander to polish, clean or remove the surface of materials can be hazardous due to the abrasive nature of the sandpaper belt and the rapid speed at which it travels. The user must take care to avoid any contact with the moving sandpaper belt, but the risk of injury can be reduced by a body element which encloses all moving parts except for the sandpaper belt. The toothed belt passes by the side of the sandpaper belt and must therefore extend the overall width of a conventional belt sander. For the sake of safety the toothed belt and wheels are enclosed by part of the body element which will consequently protrude beyond the width of the sandpaper belt if it is to accommodate the toothed belt and wheels. The additional protruding width of the body element inhibits a conventional belt sander from reaching edges and tight corners on the side of the protrusion, thereby occasionally requiring the user to rotate the belt sander through 180° in order to use the side of the belt sander on which the body element is substantially in line with the edge of the sandpaper belt. Furthermore, the additional protruding width limits the choice of aesthetic and ergonomic designs that can be applied to the body element of a conventional belt sander.
One aspect of the present invention embodies a new design of belt sander which makes use of the area located within the confines of the sandpaper belt by substituting a normal driven roller for a roller comprising an electric motor. The electric motor is located inside the roller and provides the means for driving the roller. Preferably the electric motor forms the driven roller, thus obviating the need for an additional driving mechanism such as the pulley system characterised by a toothed belt and wheels. In absence of the toothed belt and wheels the width of the belt sander body element may be reduced to no more than the width of the sandpaper belt plus the necessary means for attaching the rollers and other components located within the sandpaper belt to the body element.
The construction of electric motors is a precise task that may involve many different components, some of which are complicated to make. Electric motors like, for example, an induction motor may comprise a multiple-lamination steel rotor and a stator further comprising a complicated field coil, both of which can be a time consuming and therefore costly to manufacture. With the present invention the preferred choice of electric motor is a claw pole motor comprising an internal stator and an external rotor. The stator comprises at least one claw pole stator element and the rotor comprises at least one permanent magnet acting as a magnetic pole. The preferred choice of stator comprises three claw pole stator elements but, as would be apparent to the skilled person in the art, any number of claw pole stator elements may be employed, the number depending on, amongst other things, the available space and the type of power supply. Preferably the rotor comprises a plurality of permanent magnets and the preferred type of permanent magnet is a rare earth sintered magnet. The rare earth sintered magnet gives the advantage of greater flux density per unit volume in comparison to conventional permanent magnets, however other types of permanent magnet may

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