Tape measure having quick rewinding mechanism

Abstract

A tape measure having a quick rewinding mechanism comprises a gear assembly including a first drive gear, a second driven gear, and an idler gear set having a first, a second, a third, and a fourth idler gears each meshed with the first drive gear wherein the idler gears are equally spaced around the first drive gear for uniformly distributing a generated force to the idler gears while rewinding the tape measure device.

Description

FIELD OF THE INVENTION

[0002] The present invention relates to measuring devices and particularly to a tape measure having quick rewinding mechanism with improved characteristics.

BACKGROUND OF THE INVENTION

[0003] A conventional tape measure 1 is shown in FIGS. 1 to 3b wherein a gear assembly 20 is provided in hub, a first gear 21 is in spindle in hub, and a second driven gear 23 is on lower cap. The diameter of first gear 21 is larger than that of second driven gear 23. Two opposed shafts 311 are provided adjacent the a hole with idler gear set (i.e., idler gears 22a and 22b) sleeved on. Further, a smaller gear is meshed with first gear 21 while a larger gear is meshed with second driven gear 23. With first gear 21 and second driven gear 23 rotated about the same axis and in meshing cooperation with idler gears 22a and 22b, a quick rewinding is carried out.

[0004] However, the previous design suffered from several disadvantages. For example, idler gear (i.e., shaft 311) tend to break thus malfunctioning the gear assembly. This is best illustrated in FIG. 1. Further, tape measure tends to vibrate irregularly, thus causing an inconvenience to user. This is best illustrated in FIG. 2. After analyzed, it is found that the break of shafts 311 is caused by an excess force exerted thereon while performing a quick rewinding (see FIG. 3a and 3b). In a clockwise rewinding of tape measure, force exerted on idler gear 22a by first gear 21 has a first component force along X axis and a second component force along Y axis. In other words, a resultant force, generated along Z axis, is perpendicular to and exerted on shaft 311 (FIG. 3a). Thus shaft 311 (i.e., idler gear 22a) tends to break after a long time of use while idler gear 22b is undamaged (FIG. 1). In one consideration, the diameter of shaft 311 is increased in order to increase the durability of shaft 311. However, this may adversely affect the strength of idler gears. In another consideration, the diameters of idler gears are also increased. However, this must significantly change the construction of tape measure. Also, this will inevitably increase the size thereof. Thus, it is not practical. Moreover, first gear 21 is provided between two idler gears 22a and 22b and only supported by them. This is not a stable design as illustrated in FIG. 2. Also, such drawback is not solved even when the diameters of shafts 311 (i.e., the rotation axes of idler gears 22a and 22b) are increased. Hence, further improvement exists.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide a tape measure device having a quick rewinding mechanism comprising a gear assembly including a first drive gear, a second driven gear, and an idler gear set having a first, a second, a third, and a fourth idler gears each meshed with the first drive gear wherein the idler gears are equally spaced around the first drive gear. This can uniformly distribute a generated force to the idler gears while rewinding the tape measure device.

[0006] The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a sectional view of a conventional tape measure with a quick rewinding mechanism for illustrating a first drawback thereof (i.e., break of shaft);

[0008] FIG. 2 is a perspective view of the FIG. 1 tape measure for illustrating a second drawback thereof (i.e., irregular vibration while rewinding);

[0009] FIG. 3 a is a partial sectional view of FIG. 2 for illustrating the causes of the first drawback;

[0010] FIG. 3 b is a side view of FIG. 3a for illustrating the causes of the first drawback;

[0011] FIG. 4 is an exploded perspectve view of a tape measure having quick rewinding mechanism according to the invention; and

[0012] FIG. 5 is a side view illustrating the meshing and operation relation among gears of the FIG. 4 gear assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Referring to FIGS. 4 and 5, there is shown a tape measure having quick rewinding mechanism constructed in accordance with the invention. The characteristics of the invention is that two idler gears 22c and 22d are added to be meshed with first gear 21 in addition to the already provided idler gears 22a and 22b which are also meshed with first gear 21. As shown, four idler gears 22a, 22b, 22c, and 22d are equally spaced around first gear 21. This may distribute force generated while rewinding the tape measure uniformly to four idler gears 22a, 22b, 22c, and 22d. In detail, a component force exerted on idler gear 22a along Z axis is uniformly distributed to idler gears 22c and 22d. Hence, a dynamic balance of rotation force is carried out on gear assembly. As a result, shaft 311 does not tend to break while rewinding.

[0014] While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.

Claims

1. A tape measure device having a quick rewinding mechanism comprising a gear assembly including a first drive gear, a second driven gear, and an idler gear set having a first, a second, a third, and a fourth idler gears each meshed with said first drive gear wherein said idler gears are equally spaced around said first drive gear for uniformly distributing a generated force to said idler gears while rewinding said tape measure device.