GB2086007A

GB2086007A - Vibration Damping Handle

Info

Publication number: GB2086007A
Application number: GB8129476A
Authority: GB
Original assignee: Seto Kazuto
Current assignee: Seto Kazuto
Priority date: 1980-10-22
Filing date: 1981-09-30
Publication date: 1982-05-06
Also published as: JPS5946748B2; JPS5771784A; DE3132105A1; AU7389781A

Abstract

A vibration damping handle for use on a vibratory body (1) such as a chain saw or a rock drill, having a first mass (3, 4) mounted on the vibratory body by first resilient members such as coil springs (7) interposed between the vibratory body and the first mass to allow the latter to vibrate, and a hand grip (12) connected to the first mass and having a chamber (13) defined therein. A dynamic vibration absorber (19, 20) comprises a second mass such as a weight (17, 18) disposed in the chamber (13) of the hand grip for free vibratory motion therein, a cantilever spring (15, 16) connecting the second mass to the first mass, and the chamber in the hand grip being filled with oil for damping vibration of the second mass. <IMAGE>

Description

SPECIFICATION Vibration Damping Handle The present invention relates to vibration damping handles, and more particularly to such handles designed to adequately damp two-directional vibrations, e.g. vertical and horizontal vibrations, that are transmitted thereto from a hand-carried vibratory machine such as, for example, a chain saw or rock drill on which the handle is mounted.

Various attempts have been made to damp vibrations from the hand-grip of a hand-carried vibratory machine, such as a chain saw or rock drill. One proposal employs a vibration-proof rubber, but although this is effective to damp vibrations near its resonant frequency, it cannot adequately damp out those vibrations having the relatively high frequencies experienced with a chain saw or rock drill.

Therefore, this type of vibration damper is not suitable for use for the hand grips of these vibratory machines.

Another proposal is to use a dynamic vibration absorber having a natural frequency which is the same as the frequency of the vibrations of the vibratory machine, and which is mounted on a handle of the vibratory machine. The arrangement is such that when the machine vibrates the dynamic vibration absorber can damp out the vibrations transmitted from the vibratory machine to the handle. However, a dynamic vibration absorber of the type proposed is only effective for one-directional vibrations, and adequate vibration damping cannot be provided for the vibratory machines described above, which generally tend to vibrate in two or more directions. Thus, handles with a dynamic vibration absorber have not been satisfactory in preventing harmful vibrations of a magnitude likely to cause the machine operator to suffer from diseases caused by vibration, such as Raynaud's disease.

One object of the present invention is to provide a simple vibration damping handle which eliminates the above-described problems attendant known constructions, and adequately damp out two-directional vibrations, such as vibrations that occur with components in the vertical and horizontal directions, generated by a hand-carried vibratory machine such as a chain saw or rock drill on which the handle is mounted.

The invention consists in a vibration damping handle for use on a vibratory body which is vibratable in directions substantially perpendicular and parallel to a reference surface, said handle comprising a first mass disposed adjacent said vibratory surface by first resilient means allowing said first mass to vibrate in at least two directions, a hand-grip connected to said first mass and extending substantially parallel to said reference surface, said hand-grip containing a chamber in which a second mass is disposed in spaced relation to the wall of said chamber by second resilient means connecting said second mass to said first mass, and damping means associated with said hand-grip for damping out any vibration of said second mass.

The invention will now be described with reference to the drawings, in which: Figure 1 is a simplified, schematic perspective view of one exemplary embodiment with part of the hand grip cut away; Figure 2 is a theoretical mechanical model of the handle shown in figure 1 with respect to vertical vibrations; Figure 3 is a graph showing curves of ratios of displacement transmitted, plotted against frequency, for the mechanical model shown in figure 2; Figure 4 is an enlarged side elevation of a dynamic vibration absorber; Figure 5 is a set of graphs showing the relationship between coefficients of correction and rotational inertia for various shapes of the dynamic vibration absorber of figure 4; Figure 6 is a set of graphs showing the relationship between shapes and damping coefficients of the vibration absorber of figure 4;; Figure 7 is a graph showing a curve of a ratio of displacement transmitted when no vibration absorber is provided; Figure 8 is a graph showing a curve of a ratio of displacement transmitted when a vibration absorber is provided; Figure 9A is a graph showing a wave form of vibration plotted against time when there are impulses applied in a vertical direction and no vibration absorber is provided; Figure 9B is a graph showing a waveform of vibration plotted against time when there are impulses applied in a to-and-fro direction and no vibration absorber is provided; Figure 1 OA is a graph showing a waveform of vibration plotted against time when there are impulses applied in a vertical direction and a vibration absorber is provided;; Figure 1 OB is a graph showing a waveform of vibration plotted against time when there are impulses applied in a to-and-fro direction and a vibration absorber is provided; and Figure 11 is a simplified schematic perspective view of a second exemplary embodiment of the present invention, with part of the hand grip cut away.

With reference to figure 1, a vibratory body 1 which may comprise part of a vibratory machine such as a chain saw or rock drill, for example, is vibratable in a vertical direction, as indicated by an arrow A, substantially perpendicular to a reference surface 2 of the body 1, and in a horizontal to-andfro direction, as indicated by an arrow B, substantially parallel to the surface 2. A parallel pair of bar shaped members, 3 and 4, are mounted with their major axes in the direction B, parallel to the surface 2. A pair of inverted U-shaped frames 5 and 6, mounted on the surface 2 adjacent opposite ends of the member 3 thus surround them. The member 3 is resiliently supported with respect to the surface 2 by sets of coil springs 7, connecting each of the frames 5 and 6, and the surface 2 to each face of the member 3.Thus, four coil springs 7 are provided for each frame, 5 and 6. two extending horizontally and two vertically. Likewise, the member 4 is resiliently supported by sets of coil springs 7 in a pair of inverted U-shaped frames, 8 and 9. Thus, the members 3 and 4 are resiliently movable both vertically and horizontally with respect to the surface 2.

A pair of vertical support members 10 and 11 are mounted centrally on the members, 3 and 4, respectively. The support members 10 and 11 are linked at their upper ends by a horizontal hand grip 12 extending substantially normal to the to-and-fro direction B. The hand grip 1 2 is in the form of a hollow cylinder, with its ends sealed by the support members 10 and 11 to form a cylindrical chamber 13 that is filled with a damping material 14, such as silicone oil.From the opposite ends of the cylindrical chamber 13, there extend inwardly a pair of cantilever springs, 1 5 and 16, projecting towards each other axially within the cylindrical chamber 1 3. A pair of cylindrical weights, 1 7 and 1 8 respectively, are supported on the free ends of the cantilever springs 1 5 and 1 6, spaced from the cylindrical wall of the grip 1 2 which defines the chamber 13.

With such an arrangement, the members 3 and 4, together with the support members 10 and 11, jointly comprise a first mass, the coil springs 7 jointly comprise a first resilient means, the weights 1 7 and 1 8 jointly comprise a second mass, and the cantilever springs 1 5 and 1 6 jointly comprise a second resilient means. The cantilever spring 1 5, the weight 17, and the silicone oil 1 4 jointly comprise a dynamic vibration absorber 19, and the cantilever spring 16, the weight 18, and the silicone oil 14 jointly comprise a dynamic vibration absorber 20, and these dynamic vibration absorbers 1 9 and 20 function to damp-out any vibrations that are transmitted from the vibratory body 1 to the hand grip 12.

The operation of the vibration damping handle shown in figure 1 will now be described.

A theoretical mechanical model of the above-described handle is shown in figure 2, which model is designed for damping vertical vibrations. The model comprises a weight 23 having a mass M and supported on the vibratory body 1 by two springs, 21 and 22, each having a spring constant K/2, the weight 23 corresponding to the hand grip 12, support members 10 and 11 , and the members 3 and 4 shown in figure 1, whilst the springs 21 and 22 correspond to the two groups of eight coil springs 7.A system of a spring 24 having a spring constant k1 a damper 25 having a damping factor C1, the spring 24 and damper 25 being connected in parallel to the weight 23, and a weight 26 having a mass m and connected to the spring 24 and damper 25, corresponds to the dynamic vibration absorber 1 9.

Likewise, another system of a spring 27 having a spring constant k2, a damper 28 having a damping factor C2, and a weight 29 of a mass m2,the spring 27 and damper 28 being connected in parallel to the weights 23 and 29, corresponds to the dynamic vibration absorber 20.

The dynamic vibration absorbers 1 9 and 20 are shaped so as to be symmetrical in both the vertical and the horizontal to-and-fro directions. The handle comprising the hand grip 12, the support members 10 and 11, and the members 3 and 4 are designed to have a natural frequency which is equalised in the vertical and horizontal to-and-fro directions, and as the dynamic vibration absorbers 1 9 and 20 are adjusted optimally in the vertical direction, they are automatically adjusted in the horizontal to-and-fro direction. Thus, only vertical adjustment of the dynamic vibration absorbers will be described.

To allow the handle to have a natural frequency equalised in both the vertical and the horizontal to-and-fro directions, the coil springs 7 should be designed so that their combined spring constant in the vertical direction will be the same as the combined spring constant in the horizontal to-and-fro direction, that is, to satisfy the following equation:

where R is the effective radius of the coil springs; H is the height of the coil springs; e is the wire diameter of the coil springs; and G and E are the modulus of transverse elasticity and the modulus of longitudinal elasticity of the spring material, respectively.

Assuming that m,/M=m2/M=0.056, M=1 (kg) and K=3.55x 104 (N/m) in the mechanical model of figure 2, optimised vibration damping for the weight 23 or the complete handle requires the dynamic vibration absorbers to have their vibratory elements defined by the following optimum physical quantities according to vibration theory: m,=m2=0.56x10-' (kg) k,=1.36x103 (N/m) k2=1.98x 103 (N/m) (2) C,=2.1 (N.sec/M) C2=3.1 6 (N.sec/m).

Figure 3 illustrates curves, plotted by a computer, of ratios of displacement transmitted to the weight 23 from a vibratory body 1 which vibrates at a frequency w. The curve a is obtained when dynamic vibration absorbers with vibratory elements having the optimum values listed above at (2) are attached to the weight 23, while the curve b is obtained when no dynamic vibration absorbers are attached. From a comparison between the curves a and b, attachment of the dynamic vibration absorbers reduces the ratio of displacement transmitted from 40 db to 12 dB at the resonantfrequency wr, that is, the dynamic vibration absorbers are effective to attenuate the magnitude of vibration by about 1/2.5 of that which is experienced with no dynamic vibration absorbers provided.

Designing the dynamic vibration absorbers 19 and 20 to the optimum values of (2) will be described hereinbelow as an illustrative example.

As shown in figure 4, assuming that a weight 30 of a mass m has a diameter 2r and a height h, a cantilever spring 31 has a modulus of longitudinal elasticity Ed, the distance between the fixed end of the cantilever spring 31 and the centre of the weight 30 is I, and the geometrical moment of inertia of the cantilever spring 31 is I, the natural frequency wd of a dynamic vibration absorber D can be given by the following expression:

where a is a coefficient of correction with the rotational inertia of the weight 30 taken into account, the coefficient of correction being given by:

Figure 5 is a graph illustrative of relations given by the equation (4).With 2r=1 8 (mm), h=25 (mm) (in one example, the weight was a cylinder of copper having a diameter of 1 8 mm and a height of 25 mm, and the cantilever spring was a piano wire having a diameter of 1.6 mm), effective spring lengths 1" 12 which satisfy optimum spring constants k,=1.36x 103 (N/m) and k2=1.98x 103 (N/m) will be l,=51.8 (mm) and 12=45.4 (mm) from the graph of figure 5.

Figure 6 shows actual measurements plotted for the damping factor C of a cylinder as it vibrates radially in a pipe, the cylinder having a diameter d and a height h and being disposed coaxially within the pipe, and the pipe having an internal diameter D=26 mm and being filled with turbine oil having a kinematic viscosity V=5 x 0-4 m2/sec. White dots are indicative of values measured when d=22 mm, squares indicate values measured when d=20 mm, triangles indicate measurements when d=1 8 mm, and black dots are indicative of measurements when d=1 6 mm. Such measured values are approximated by the straight lines in the graph from which there is derived the following practical approximate expression:

where the units are m2/s for V, mm for h, mm ford, and mm for D.

From the expression (5), oil with a kinematic viscosity V=6.3x 10-4 m2/sec should be used for the value of C=2.1 N.sec/m with d=1 8 mm, h=25 mm, such oil being obtained by mixing two kinds of silicone oil having V=l Ox 1 0-4 m2/sec and V=5 x 10-4 m2/sec, respectively.

An experiment was conducted on a handle assembly prototype designed as described above. The experiment was carried out by vibrating the vibratory body 1 with a hydraulic vibrator to allow accelerometers mounted centrally on the vibratory body 1 and the grip member 12 to produce signals which were analysed by a transfer function analyser to obtain ratios of displacement transmitted.

Figure 7 shows a curve of ratios of displacement transmitted when no vibration absorber is provided, and figure 8 shows a curve of ratios of displacement transmitted when vibration absorbers are provided. It will be understood from a comparison between figures 7, 8 and 3 that theoretical values of figure 3 are substantially in conformity with experimental values of figures 7 and 8. The experimental measurements show that the vibration absorbers provided were highly effective in reducing the maximum ratio of displacement transmitted at the resonant frequency (30 Hz) from 70 times (37 dB) when no dynamic vibration absorber is provided down to 4 times (12 dB) with the vibration absorbers provided, an attenuation to about 1/18 of the magnitude experienced when no dynamic vibration absorber is provided.

To determine if the dynamic vibration absorbers can suppress vibrations in the horizontal to-andfro direction as well as in the vertical direction, the hand grip 1 2 was struck centrally thereof in the vertical and horizontal to-and-fro directions in an experiment to review impulse responsiveness of the handle assembly, the results being shown in figures 9(A) and (B) for no absorber, and figures 10(A) and (B) with an absorber.

Figures 9(A) and (B) illustrate waveforms of vibration of the handle in response to an impact applied in the vertical and the horizontal to-and-fro directions, respectively, and with no vibration absorber provided, whilst figures 1 0(A) and (B) illustrate waveforms of vibration of the handle in response to an impact applied in the vertical and horizontal to-and-fro directions respectively with vibration absorbers provided. The curves in figures 10(A) and (B) indicate that the dynamic vibration absorbers can suppress vibrations substantially equally in the vertical and horizontal to-and-fro directions.

Various modifications may be made in the embodiment described hereinabove. For example, there may be only one dynamic vibration absorber. As shown in figure 11 , furthermore, a handle may comprise a single support member 32, with a cruciform lower member 33. An additional dynamic vibration absorber 34 which is symmetrical in both the horizontal to-and-fro and the lateral directions may be mounted in a hollow support member 32 for vibration damping in the horizontal direction indicated by an arrow C which extends perpendicularly to the to-and-fro direction B, in addition to the damping provided in the vertical and horizontal directions A and B. With such an arrangement, the weights 35 and 36 may be shaped for optimised operation.

It should be understood that in actual use the handle shown in figure 1 can be inclined, or turned upside-down without adversely affecting vibration damping of the handle.

Vibratory motion of the second mass (the weights 1 7 and 1 8) may be reduced by magnetic damping. For example, the weights 1 7 and 1 8 may be made of an electrically conductive material, and a magnet may be mounted on the hand grip 12 to produce a magnetic flux extending perpendicularly to a cylindrical side wall of the weights 17 and 18.

Claims

1. A vibration damping handle for use on a vibratory body which is vibratable in directions substantially perpendicular and parallel to a reference surface, said handle comprising a first mass disposed adjacent said vibratory surface by first resilient means allowing said first mass to vibrate in at least two directions, a hand grip connected to said first mass and extending substantially parallel to said reference surface, said hand grip containing a chamber in which a second mass is disposed in spaced relation to the wall of said chamber by second resilient means connecting said second mass to said first mass, and damping means associated with said hand grip for damping out any vibration of said second mass.

2. A vibration damping handle as claimed in claim 1, in which said damping means comprises a damping material filling said chamber in said hand grip.

3. A vibration damping handle as claimed in claim 1, in which said second mass is made of an electrically conductive material and said damping means comprises a magnet mounted on said hand grip to produce a magnetic flux extending substantially perpendicularly to said second mass.

4. A vibration damping handle substantially as described with reference to figure 1 or figure 11.