GB2382856A

GB2382856A - A device for damping the vibrations of a handgrip of a power-driven tool

Info

Publication number: GB2382856A
Application number: GB0227112A
Authority: GB
Inventors: Karl Bendel; Martin Fischer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-11-28
Filing date: 2002-11-20
Publication date: 2003-06-11
Anticipated expiration: 2022-11-20
Also published as: CH695853A5; GB0227112D0; GB2382856B; JP2003170370A; DE10158266A1; DE10158266B4

Abstract

A handgrip 3 of a power-driven tool 1 is connected to a housing 2 of the power-driven tool 1 by means of at least one spring 4. An actuator 5 acts on the spring 4 , the actuator 5 being able to adjust the preload of the spring 4 so that the distance between the handgrip 3 and the housing 2 of the power-driven tool 1 remains practically constant independently of the operating force 6 exerted on the handgrip 3. The force exerted by the actuator 5 on the spring 4 is controlled by a feed-back control arrangement 7, 8, 9, 10.

Description

Device for vibration-damping of a handgrip of a power-driven tool State of the art The present invention relates to a device for vibrationdamping of a handgrip of a power-driven tool, wherein the handgrip is connected by means of at least one spring to the housing of the power-driven tool.

In particular in the case of power-driven tools with a percussion drive, for example hammer drills, chisel hammers and the like, very strong vibrations are produced in the machine which are transmitted to the handgrip of the machine and are not only unpleasant for the operator but can also be damaging to health. Passively and actively acting devices by which the handgrip of a power-driven tool can be uncoupled to a greater or lesser degree with respect to vibrations of the machine are already known from the state of the art.

In the case of passively acting devices, as emerges, for example, from DE 41 24 574 Al, individual springs or spring systems are interposed between the handgrip and the housing of the power-driven tool. Good uncoupling requires the softest possible spring. A variation of the pressure exerted by an operator on the handgrip therefore causes especially large differences in the distance between the handgrip and

the housing of the power-driven tool. Bottoming of the handgrip on a stop on the machine housing therefore frequently occurs. In such situations the uncoupling between the handgrip and the machine housing is completely abolished.

A very high degree of independence of the vibrational uncoupling with respect to the operating force applied to the handgrip can be attained by means of active devices. Such an active device for vibrational uncoupling of the handgrip of a power-driven tool is described, for example, in EP 0 206 981 A2. The active device for vibrational uncoupling disclosed by this document consists of an actuator in the form of an electromagnet connecting the handgrip to the housing of the power-driven tool, the force of which electromagnet is controllable as a function of the position of the handgrip with respect to the housing of the powerdriven tool. For this purpose a feedback control system is provided which is controlled, for example, by means of a signal of a system for measuring the travel of the handgrip with respect to the housing. In this way a large distance between the handgrip and the housing can be set when the operating pressure is low and a small distance can be set when the operating pressure is high.

An active uncoupling between the handgrip and the housing of a power-driven tool is also disclosed by WO 98/21014. Here, the force exerted by an actuator is so controlled as a function of the acceleration of the machine housing that, independently of the oscillations of the machine housing, the handgrip does not move. For this purpose a feedback control system is provided which is controlled by means of an acceleration sensor in the handgrip and the operating

pressure exerted by the operator on the handgrip is compensated by means of a strong spring.

The above-mentioned devices in which the vibrational uncoupling is effected by means of actuators require relatively high electric power for the electric drive of the actuators. Furthermore, such vibration damping arrangements are effective only within a very restricted vibration frequency band because of a certain sluggishness of the actuators. These purely active, electrically-driven vibration-damping arrangements also require relatively costly control circuitry.

Advantages of the invention A vibration-damping device according to the invention for a handgrip of a power-driven tool consists according to the features of Claim 1 in that the handgrip is connected to the housing of the power-driven tool by means of at least one spring and in that an actuator acting on the spring is present, by means of which actuator the preloading of the spring is so adjustable that the distance between the handgrip and the housing of the power-driven tool remains practically constant independently of the operating force exerted on the handgrip.

Unlike known actuators which regulate the distance between the handgrip and the housing of the power-driven tool in a vibration-damping manner, the actuator used according to the invention, which only adjusts the preloading of a spring, is realisable with considerably less technical complexity and

requires only low electrical power for its operation. As a result of the adjustment of the spring preload by means of an actuator the distance between the handgrip and the powerdriven tool can be kept largely constant despite a changing operating force exerted on the handgrip, whereby a very high degree of vibrational uncoupling of the handgrip with respect to the housing of the power-driven tool is achieved. The cost of the control technology of the device according to the invention is very low.

Advantageous embodiments and further developments of the invention emerge from the subsidiary claims.

In order to be able to keep the distance between the handgrip and the housing of the power-driven tool practically constant independently of the operating force exerted on the handgrip, it is useful to provide means which control or regulate a force exerted by the actuator on the spring to adjust its preloading as a function of the distance between the handgrip and the housing of the power-driven tool, or as a function of the force of pressure prevailing between the handgrip and the housing of the power-driven tool.

An advantageous embodiment of the actuator consists in that it has a plunger acting on the spring, which plunger is displaceable by means of an electromagnetic or hydraulic or pneumatic drive.

The actuator can be arranged either on or in the handgrip, or on or in the housing of the power-driven tool.

Drawings The invention is explained in more detail below with reference to a number of embodiments represented in the drawings, in which: Fig. 1 is a schematic diagram of a device which uncouples the handgrip of a power-driven tool in a vibration-damping manner with respect to the power-driven tool, Fig. 2 shows a vibration-damping device the actuator of which is arranged in the handgrip, the actuator being activated by a displacement sensor signal, Fig. 3 shows a vibration-damping device the actuator of which is arranged in the housing of the power-driven tool, the actuator being activated by a displacement sensor signal, and Fig. 4 shows a vibration-damping device the actuator of which is activated by a force sensor signal.

Description of embodiments Fig. 1 is a schematic diagram of a power-driven tool 1, for example a hammer drill or chisel hammer, etc. , with a housing 2 accommodating a drive for the tool and with a handgrip 3 coupled to the housing 2. During the work process the housing 2 can be subjected to very strong vibrations which without vibration-damping measures are transmitted to the handgrip 3.

The device illustrated in Fig. 1 is designed to effect the most extensive possible vibrational uncoupling of the handgrip 3 from the housing 2 of the power-driven tool. This vibrational uncoupling device has a spring or a spring system 4 consisting of a plurality of springs arranged between the housing 2 and the handgrip 3. This device also includes an

actuator 5 with which the preload of the spring 4 is variably adjustable. The objective is so to activate the actuator 5 that it so adjusts the preload of the spring 4 that the distance between the housing 2 of the power-driven tool and the handgrip 3 remains practically constant independently of an operating force 6 exerted on the handgrip 3. In order accordingly to activate the actuator 5, a control unit 7 is provided which derives a positioning value y for the actuator 5 from a control value x supplied by a sensor 8 and a preset reference value xs stored in the control unit 7. The reference value xs is a distance to be maintained between the housing 2 of the power-driven tool and the handgrip 3.

The sensor 8 is either a displacement sensor which captures the actual distance x between the housing 2 and the handgrip 3, or the sensor 8 can be a pressure sensor with which the operating force 6 with which the handgrip 3 is moved towards the housing 2 can be measured.

A positioning value y for the actuator 5 is derived by the control unit 7 from the deviation between the actual value x of the operating force and the preset reference value xs, so that said actuator 5 so adjusts the preloading of the spring 4 that the distance between the housing 2 and the handgrip 3 remains practically constant. The control unit 7 includes a low-pass filter 9 and a variable-gain amplifier 10. The lowpass filter 9 is attuned to a pass range for the frequency of the varying operating force. At a frequency of 50 Hz usually occurring in the case of a hammer drill or a jackhammer the upper edge frequency of the low-pass filter should be approx.

15 Hz.

It is precisely the frequencies of the changing operating force 6 that must be corrected by the actuator 5 adjusting the preload of the spring 4. The vibrational frequencies above this value are largely absorbed by the spring 4.

A number of concrete embodiments of the arrangement and implementation of the actuator 5 and embodiments of the sensor 8 will now be described with reference to Figs. 2,3 and 4. In Figs 2 to 4 the elements of the vibration-damping device mentioned in connection with Fig. 1 are denoted by the same reference characters as in Fig. 1.

Fig. 2, like Figs. 3 and 4 to be described later, shows a cutaway portion of the housing 2 of a power-driven tool and the handgrip 3 coupled thereto. The actuator 5 adjusting the preload of the spring 4 is located in the handgrip 3. The actuator has a plunger 11 which is displaceable by means of an electromagnetic or hydraulic or pneumatic drive. The spring 4 is, for example, a helical spring which on one side is mounted on a spigot 12 arranged on the housing 2 and is fixed thereto. On the other side the helical spring 4 is mounted on the plunger 11 of the actuator 5 where it bears against a stop 13. By movement of the plunger 11 of the actuator 5 the helical spring 4 is compressed more or less strongly, whereby its preload is changed. Instead of a helical spring 4 a spring washer or leaf spring attached to the housing 2 and to the plunger 11 of the actuator 5 can also be used. It is also possible to provide a spring system consisting of a plurality of springs instead of only one spring. Likewise, the handgrip 3 can be coupled in a vibration-damping manner to the housing 2 by means of a

plurality of springs and a plurality of actuators 5 acting thereon.

Between the handgrip 3 and the housing 2 is inserted a displacement sensor 14 which captures the distance between the handgrip 3 and the housing 2 as a control value x. The displacement sensor 14 can be based, for example, on the principle that a sensing spindle 15 is displaced according to the distance between the handgrip 3 and the housing 2 and this displacement is measured, for example, inductively.

However, any other type of displacement sensor can be used to measure the distance between the handgrip 3 and the housing 2.

The embodiment illustrated in Fig. 3 differs from that in Fig. 2 in that the actuator 5 with the associated control unit 7 is arranged in the housing 2 and not in the handgrip 3 of the power-driven tool.

As described above a force sensor can be used instead of a displacement sensor 14, which force sensor captures the force of pressure between the handgrip 3 and the housing 2. An embodiment of the force sensor can consist, for example, in that the stop 13 on the plunger 11 of the actuator 5 reacts to the pressure of the spring 4 bearing thereon. For example, the stop 13 could consist of a material the electric resistance of which changes as a function of a force acting upon it. The pressure-dependent resistance change of the stop 13 is captured as the control value x and supplied to the control unit 7.

The actuator for adjusting the spring preload can also consist, for example, of the motor present in the powerdriven tool and a spindle driven thereby, which acts on the spring. Specifically, the spindle is reciprocatingly movable by means of the motor in the direction of the spring axis.

For this purpose a coupling can be provided which converts the rotation of the motor shaft into a longitudinal motion of the spindle. The coupling can be so controlled that it applies a clockwise or anticlockwise rotation to the spindle as a function of the distance between the handgrip and the machine housing, depending on whether the spindle is to be moved out or in.

Claims

1. A device for vibration-damping of a handgrip of a power- driven tool wherein the handgrip (3) is connected to the housing (2) of the power-driven tool (1) by means of at least one spring (4), characterised in that an actuator (5) acting on the spring (4) is present, with which actuator (5) the preloading of the spring (4) is so adjustable that the distance between the handgrip (3) and the housing (2) of the power-driven tool (1) remains practically constant independently of the operating force (6) exerted on the handgrip (3).

2. A device according to Claim 1, characterised in that means (7,8, 14,15) are present which control or regulate a force exerted by the actuator (5) on the spring (4), which force adjusts the preload of said spring (4) as a function of the distance between the handgrip (3) and the housing (2) of the power-driven tool (1).

3. A device according to Claim 1, characterised in that means (7,8, 13) are present which control or regulate a force exerted by the actuator (5) on the spring (4), which force adjusts the preload of said spring (4) as a function of the force of pressure prevailing between the handgrip (3) and the housing (2) of the power-driven tool (1).

4. A device according to one of the preceding claims, characterised in that the actuator (5) has a plunger (11) acting on the spring (4), which plunger (11) is displaceable by means of an electromagnetic or hydraulic or pneumatic drive.

5. A device according to one of claims 1 to 4, characterised in that the actuator (5) is arranged on or in the handgrip (3).

6. A device according to one of claims 1 to 4, characterised in that the actuator (5) is arranged on or in the housing (2) of the power-driven tool (1).

7. A device for vibration-damping of a handgrip of a power- driven tool substantially as herein described with reference to the accompanying drawings.