WO2005090008A1

WO2005090008A1 - Power tool

Info

Publication number: WO2005090008A1
Application number: PCT/SE2005/000342
Authority: WO
Inventors: Carl Ribbing
Original assignee: Carl Ribbing
Priority date: 2004-03-22
Filing date: 2005-03-08
Publication date: 2005-09-29
Also published as: SE0400719L; SE0400719D0; CA2560302A1; CN1942287A; SE528362C2

Abstract

A power tool having a handle (12) and an active portion (18) for engagement with a work piece. To optimize the engagement forces of the tool and to provide an open top side allowing for alternative gripping, the handle (12) and the active portion (18) are joined in a substantially U-shaped configuration, where the handle and the active portion form free ends at respective tops thereof, and that the active portion is located such that the rotational axis lies on a level below said top.

Description

Title: Power tool

Technical field

This invention relates to a power tool comprising a handle and an active portion for engagement with a work piece.

Background

In power tools, i.e. hand tools having any kind of driving mechanism, for example, power drills, screw and nut drivers or grinders, the tool transfers work or power to the work piece. The rotational force imparts a torque to the tool. When the tool is used, a force is applied straight forward by the user's hand to push the rotating active portion against the work piece. For screwdrivers and drills, the necessary axial force sometimes amounts up to 100 N.

There are many different types of power tools having handles of different shapes and locations. In order to demonstrate the importance of the position of the handle in relation to the axis of the rotating part, a short analysis of some of the forces that may appear in the tool is given below. Compared are forces between a conventional power drill and that of the present invention as shown in FIG. 1.

A conventional power drill/screwdriver has a handle positioned so that the top portion of the user's hand will be located a few centimeters below the rotational axis of the chuck. The following simple analysis will show that in order to apply a force that is directed exclusively along the axis of the chuck, one has to combine a forward pushing force with a downward turning force. This analysis does not account for the rotational force of the operating tool and not for the weight of the tool but is intended to illustrate one of the problems to be solved by the present invention.

Most easy is to analyze the forces acting in two points, namely the tool bit tip and the lower portion of the user's wrist. In the absence of any downward turning force from the wrist, the force f in the bit tip will be directed, as shown in FIG. 2, along a line from the wrist to the bit tip. According to FIG. 2, this force can be divided into two components, a straight forward directed horisontal force f(h) =f cos(a) and a straight upward directed vertical force f(v) =f sin(a). The upward directed force may cause a drilled hole to be oval or a driven screw to be deflected upwards. To eliminate the upward force, a downward torque M may be applied from the user's wrist. In the tool bit tip, this torque results in a force designated by f(m) and perpendicular to the pushing force. When f(m) is sufficiently large to compensate for f(v), it will be f(m) = f tan(a) = f x/y = IWr as a function of the distances x, y, r and the torque M around the point m. The total force f(t) directed exclusively forward is then f(t) = f/cos(a) whereby the pushing force f must be f = f(t) cos(a) and the torque M M = f(m) r = f(t) x

Thus, the rotational force f(m) is the pushing force f multiplied by x/y. The torque M is f(t) multiplied by x and is independent from y. It may seem that such a large value of y should decrease the necessary torque M, while a large value of y only decreases the angle a so that, in practice, it will be less important to fully reduce f(m) from f(v).

Typical values of x and y for a traditional screwdriver are x=11 and y=23, whereby r=25.5 cm and angle a=25.5 degrees. If a total force f(t) =100 N is desired, then f=90 N, f(m)=43 N and M=11 Nm. These values show that a large turning force is required to obtain a straight forward force: First a pushing force of 90 N has to be applied, and this pushing force must be combined with a downward force of 43 N having a torque of 1 1 Nm to compensate for f(v). Supposing a lever arm of 5 cm at the user's wrist, the torque of 11 Nm gives rise to 220 N corresponding to the total force developed in the wrist. At these typical values, the conclusion is that only 45% of the total force in the wrist is used in the tool bit tip if the force is to be directed along the tool rotational axis.

If x is decreased to 7 cm and the angle to 16.9 degrees, which are typical values for the present invention, the result is f=96 N, f(m)=29 N and M=7 Nm. In the same manner now 7 Nm using a lever arm of 5 cm corresponds to 140 N. Accordingly, 71 % of the applied force is utilized, and efficiency increases by 57% compared to the previously described conventional power tool.

As mentioned above, there are many different types of power hand tools. Some have their handles positioned so as to reduce the upward torque as shown above, for example, certain types of hammer drills where the handle is positioned at the rear end with the upper part of the handle in line with the chuck axis. Some power drills also have a handle that allows for placing the hand near the axis f the chuck. Disclosure of the invention

According to an aspect of the invention, the handle and the active portion are connected in a substantially U-shaped configuration, where the handle and the active portion form free ends at respective top portions thereof, and the active portion is located so that the rotational axis lies on a level below said top portions.

Accordingly, a novel feature of this invention is that the handle, in addition of optimizing the forces as described above, has an open top allowing alternative ways of gripping the handle.

Moreover, it is possible to easily make the active portion tumable to the sides so that the tool may be used in sideway directions for increased accessibility.

Other features and advantages with the invention will be apparent from the following description and the claims.

Brief description of the drawing

FIG. 1 is a rear oblique view of a power tool according to the invention;

FIG. 2 is a graphical analysis of forces present when using the power tool;

FIGS. 3 and 4 show two different ways of holding a power tool according to the invention; and

FIG. 5 is a lateral view of a tumable link between the active portion and the power tool.

Detailed description

The power hand tool generally designated by 10 in FIG. 1 has a handle 12 and an active portion 18 connected in a substantially U-shaped configuration where the handle 12 has an upward free end and the active portion 18 forms a second upward free end. "Active portion" 18 is to be understood as the part of the tool which interacts with the work piece material by, for example, a chuck 20 of a power drill. By such a configuration according to FIG. 1 , the distance from a user's wrist to the rotationa l axis 20 of the power tool is reduced so as to transfer the applied force to the work piece material in a direction along the axis 20. In addition, there is a possibility of an alternative way of grasping the handle, FIG. 4, where the user's palm is supporting the upper portion of the rear face of the handle and the fingers are placed over the top of the handle. By using this grip it is possible to use the power tool on a high level without having to flex the wrist, which is a problem with the conventional type of power tool, where the wrist is flexed up to 45 degrees when working at high levels. The lower part 16 of the tool section including the active portion 18 is adapted for being capable of use in a two-handed grip. As there is a large distance between the rotational axis and the second grip, the torque from the rotation of the motor 28 to the chuck 20 may be handled. Further, the upward torque described in the introduction of this description, can be entirely eliminated by the two-handed grip forming a lever where the second hand is holding back so that pushing force is applied from the first hand only.

In order that the handle 12 should provide an optimal grip it is formed with two vertical portions 32, 34 joined by a curved portion 36. The vertical portions allow application of forward force, and at the same make time it possible to incline the hand by being laterally offset to each other by a distance D1 of about 1-3 cm. The handle 12 is connected to the reminder of the power tool in such a manner that the front face of the handle is ended at a higher level than the rear face by a distance D2 of about 1-3 cm which allows for a compact grip and a structure of a higher strength.

Power hand tools of this type are sometimes used in areas of low accessibility. To facilitate such use, the present invention makes it possible to make the active portion tumable sideways. The active portion 18, FIG. 1 , shows the portion that can be arranged as a linkage 26 rotatable to the sides so that the power tool can be used in a lateral direction. FIG. 5 shows in detail how such linkage 26 can be constructed. It is comprised of two parts where one part may be clamped by a screw. It is suitable to have an arresting function at a 90 degree rotational position in both directions, for example by spring-loaded balls locking in grooves at 0 and 90 degrees. The required free space behind the chuck at a 90 degree rotation will then be small

List of reference-numbered parts

10. Power tool

12. Handle

14. Trigger

16. Two-handed hand grip

18. Active portion

20. Chuck or holder defining the rotational axis

24. Gearbox

26. Turnable coupling between power tool and active portion

28. Motor

30. Battery unit

D1. Distance between top and bottom portion of handle

D2. Distance between front and rear handle attachment

Claims

1. A power tool comprising a handle and an active portion for engagement with a work piece, c h a r a c t e r i z e d in that the handle (12) and the active portion (18) are joined in a substantially U-shaped configuration, where the handle and the active portion form free ends at respective tops thereof, and that the active portion is located such that the rotational axis lies on a level below said top.

2. The power tool according to claim 1 , wherein the rotational axis lies on a level between the top and at least the half of the handle (12).

3. The power tool according to claim 1 or 2, comprising a trigger provided at a front face and at the free end of the handle (12) to be controlled from above or laterally by at least one user finger.

4. The power tool according to any of the previous claims, wherein the active portion (18) is arranged turnable around a shaft substantially perpendicular to said rotational axis.

5. The power tool according to claim 4, wherein said shaft is a drive shaft for the power tool.

6. The power tool according to any of the previous claims, comprising a battery pack (30) located below the handle (12) in a manner to localize the center of gravity of the power tool.

7. The power tool according to any of the previous claims, wherein the rear face of the power tool has a shape defined by two substantially vertical portions (32, 34) located at the top and at the bottom of the handle, said vertical portions (32, 34) being joined by a curved portion (36) in such a manner that an upper portion (34) of the substantially vertical portions lies a distance (D1) closer than a lower portion (32) of the substantially vertical portions.

8. The power tool according to any of the previous claims, wherein the handle is connected to the power tool in such a manner that at front face of the handle (12) is ended at a level situated a distance (D2) higher than a rear face of the handle.

9. A handle according to claims 7 or 8, wherein said distance (D1 , D2) is about 1- 3 cm.