GB1602596A - Vibration-including devices - Google Patents

Description

(54) VIBRATION-INDUCING DEVICES (71) We, VIBRATECHNIQUES LIMITED, of New England House, Brighton, BNI 4GH, Sussex, a British Company, do hereby declare the invention for which we pry that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to vibrationinducing devices and has been devised with the general object of providing a rotary action vibration-inducing device in which the frequency of the vibration which can be applied can be varied whilst maintaining a relatively constant centrifugal force, this effect being advantageous compared with known devices utilising a fixed eccentrically mounted weight where the centrifugal force is proportional to the square of the rotational speed.

Thus in accordance with the invention there is proposed a vibration-inducing device comprising a rotor coupled to a motor and having a centre of gravity eccentrically disposed relative to the axis of rotation of the rotor, said rotor having a back plate with a compensating weight pivotally mounted thereon for angular movement relative thereto about an axis offset from the axis of rotation, there being also mounted on the back plate a cylinder containing a piston and a resilient member, the piston being movable in one direction in the cylinder by thrust transmitted by the compensating weight, the resilient member serving to control the movement of the piston and thereby the movement of the compensating weight under the influence of centrifugal force as the rotational speed of the rotor increases.

Preferably the compensating weight has a heel portion which acts on the said piston through the intermediary of a ball, and the resilient member is a plug made of synthetic rubber-like material.

In order that the nature of the invention may be more clearly understood however, there is hereinafter described by way of illustrative example an even more fully developed and preferred embodiment of the invention which is illustrated in the accompanying drawings, in which: Fig. 1 is an end elevation partly in section of a vibration inducing device; Fig. 2 is a view similar to Fig. 1 showing moving parts of the device in an alternative position; Fig. 3 is a side elevation of the device; and Fig. 4 is a plan view.

Referring now to the drawings, the vibration inducing device comprises a flat mounting plate 1 which supports an electric motor 2 and a pedestal 3. The pedestal 3 contains a bearing 4 which supports the boss 5a of a circular back plate 5 which is fixed to the motor shaft 6.

Pivotally attached to the outward face of the back plate 5 at a point P (Figs. 1 and 2) which lies closer to the rim of the back plate than to its centre is a movable weight 8 comprised of a relatively thin stem 8a an enlarged head 8b and a heel portion 8c. The centre of gravity of the weight 8 is indicated at C in Figs. 1 and 2.

The heel portion 8c of the weight 8 is in contact with a ball bearing 9 partly located in an end cavity of a piston 10 which is slidable in a cylinder 11. The end of this cylinder 11 is closed by an adjustable stop 12 having a screw driver slot 1 2a and between the stop 12 and the piston 10 is a resilient buffer 13 made of a synthetic rubber polyurethane material known as "Avothane" (Registered Trade Mark).

The theory and mode of operation of the vibration inducing device at different rotational speeds is hereinafter described.

The centrifugal force which is developed can be calculated from the formula: Wv2 Centrifugal Force=-----=.00034 WrN2 (lbf) 9r where W=eccentric weight in Ibs.

r=radius to centre of gravity of eccentric in feet N=speed in revolutions per minute v=velocity in feet per second.

The centrifugal force always acts radially outwards through the centre of gravity of the eccentric mass.

The moving weight (MW)8 is designed so that when it is rotated at a slow speed (Fig. 1 position) its centre of gravity C is just above the X-X axis and very near the centre of rotation of the backplate 5. In addition if the MW was rotated about pivot P in a clockwise direction the centre of gravity would traverse an arc which crosses the YY axis.

If all components apart from the moving weight 8 are considered as constituting the Fixed Weight (FW), the centre of gravity D of this FW can be adjusted--e.g. by adding mass to the backplate 5-so that it has a position in the lower right quadrant of the grid defined by the axes X-X and Y-Y.

At low speed (Fig. 1) the centrifugal force produced by the MW8 is very small as the distance r in the centrifugal force calculation is very close to the centre of rotation. For the FW the distance r and also its weight W are larger and the centrifugal force produced is very much greater than that of the moving weight 8. The resultant centrifugal force can be calculated by resolving the two centrifugal forces. The centrifugal force of the MW8 is small and in such a position that it makes little difference to the resultant.

At higher speeds the centrifugal force of the moving weight 8 causes it to move outwards, rotating about the point P against the resilient action of the buffer 13. In doing so its radius of eccentricity is increased and the centrifugal force it produces becomes greater by comparison with that produced by the FW. Also as the MW rotates its centre of gravity moves whilst the centre of gravity of the FW moves in the opposite direction, due to movement of the piston 10.

This causes the two centrifugal forces to oppose each other more directlv so that the centrifugal force due to the moving weight 8 (MW) has more effect on reducing the overall centrifugal force.

Fig. 2 shows the state of affairs at maximum speed (e.g. 6000 r.p.m.). In this condition it has been arranged that the centre of gravity of both the moving weight and the fixed weight are on the Y-Y axis and therefore the resultant centrifugal force is calculated by subtracting the centrifugal force of the moving weight from the centrifugal force of the fixed weight. The centre of gravity of the fixed weight has moved to D' due to the movement of the piston 10 and the buffer 13.

Although the centrifugal force of the fixed weight has increased with the square of the speed, ignoring the change in the radius of eccentricity, the centrifugal force of the moving weight has increased by a far greater amount and is arranged so that the resultant centrifugal force from 2000 r.p.m.

to 6000 r.p.m. remains almost constant.

The device as above described is advantageous in that it is effective throughout a designated speed range.

For vibrators with fixed eccentric weights the centrifugal force increases with the square of the rotational speed and these vibrators are designed so that the maximum centrifugal force of which they are capable occurs at their maximum running speed, even though the eccentric weight can be adjusted with the vibrator stationary. By having a large eccentric mass at low speeds the centrifugal force at low speeds can be increased. As the speed increases the increase in centrifugal force of the fixed weight is counteracted by that of the moving weight. This produces a resultant centrifugal force which remains approximately constant over a given speed range, in the instance described from 2000 to 6000 r.p.m.

WHAT WE CLAIM IS: 1. A vibration-inducing device comprising a rotor coupled to a motor and having a centre of gravity eccentrically disposed relative to the axis of rotation of the rotor, said rotor having a back plate with a compensating weight pivotally mounted thereon for angular movement relative thereto about an axis offset from the axis of rotation, there being also mounted on the back plate a cylinder containing a piston and a resilient member, the piston being movable in one direction in the cylinder by thrust transmitted by the compensating weight, the resilient member serving to control the movement of the piston and thereby the movement of the compensating weight under the influence of centrifugal force as the rotational speed of the rotor increases.

2. A device according to claim 1 wherein the compensating weight has a heel portion which acts on the said piston through the intermediary of a ball.

3. A device according to Claim 1 or Claim 2 wherein the resilient member is a plug made of synthetic rubber-like material.

4. A vibration-inducing device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. The centrifugal force always acts radially outwards through the centre of gravity of the eccentric mass. The moving weight (MW)8 is designed so that when it is rotated at a slow speed (Fig. 1 position) its centre of gravity C is just above the X-X axis and very near the centre of rotation of the backplate 5. In addition if the MW was rotated about pivot P in a clockwise direction the centre of gravity would traverse an arc which crosses the YY axis. If all components apart from the moving weight 8 are considered as constituting the Fixed Weight (FW), the centre of gravity D of this FW can be adjusted--e.g. by adding mass to the backplate 5-so that it has a position in the lower right quadrant of the grid defined by the axes X-X and Y-Y. At low speed (Fig. 1) the centrifugal force produced by the MW8 is very small as the distance r in the centrifugal force calculation is very close to the centre of rotation. For the FW the distance r and also its weight W are larger and the centrifugal force produced is very much greater than that of the moving weight 8. The resultant centrifugal force can be calculated by resolving the two centrifugal forces. The centrifugal force of the MW8 is small and in such a position that it makes little difference to the resultant. At higher speeds the centrifugal force of the moving weight 8 causes it to move outwards, rotating about the point P against the resilient action of the buffer 13. In doing so its radius of eccentricity is increased and the centrifugal force it produces becomes greater by comparison with that produced by the FW. Also as the MW rotates its centre of gravity moves whilst the centre of gravity of the FW moves in the opposite direction, due to movement of the piston 10. This causes the two centrifugal forces to oppose each other more directlv so that the centrifugal force due to the moving weight 8 (MW) has more effect on reducing the overall centrifugal force. Fig. 2 shows the state of affairs at maximum speed (e.g. 6000 r.p.m.). In this condition it has been arranged that the centre of gravity of both the moving weight and the fixed weight are on the Y-Y axis and therefore the resultant centrifugal force is calculated by subtracting the centrifugal force of the moving weight from the centrifugal force of the fixed weight. The centre of gravity of the fixed weight has moved to D' due to the movement of the piston 10 and the buffer 13. Although the centrifugal force of the fixed weight has increased with the square of the speed, ignoring the change in the radius of eccentricity, the centrifugal force of the moving weight has increased by a far greater amount and is arranged so that the resultant centrifugal force from 2000 r.p.m. to 6000 r.p.m. remains almost constant. The device as above described is advantageous in that it is effective throughout a designated speed range. For vibrators with fixed eccentric weights the centrifugal force increases with the square of the rotational speed and these vibrators are designed so that the maximum centrifugal force of which they are capable occurs at their maximum running speed, even though the eccentric weight can be adjusted with the vibrator stationary. By having a large eccentric mass at low speeds the centrifugal force at low speeds can be increased. As the speed increases the increase in centrifugal force of the fixed weight is counteracted by that of the moving weight. This produces a resultant centrifugal force which remains approximately constant over a given speed range, in the instance described from 2000 to 6000 r.p.m. WHAT WE CLAIM IS:

1. A vibration-inducing device comprising a rotor coupled to a motor and having a centre of gravity eccentrically disposed relative to the axis of rotation of the rotor, said rotor having a back plate with a compensating weight pivotally mounted thereon for angular movement relative thereto about an axis offset from the axis of rotation, there being also mounted on the back plate a cylinder containing a piston and a resilient member, the piston being movable in one direction in the cylinder by thrust transmitted by the compensating weight, the resilient member serving to control the movement of the piston and thereby the movement of the compensating weight under the influence of centrifugal force as the rotational speed of the rotor increases.

2. A device according to claim 1 wherein the compensating weight has a heel portion which acts on the said piston through the intermediary of a ball.

3. A device according to Claim 1 or Claim 2 wherein the resilient member is a plug made of synthetic rubber-like material.

4. A vibration-inducing device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.