GB2411375A

GB2411375A - Vibration reduction in pneumatic tools.

Info

Publication number: GB2411375A
Application number: GB0404246A
Authority: GB
Inventors: Roy Wyatt
Original assignee: South West Highways Ltd
Current assignee: South West Highways Ltd
Priority date: 2004-02-26
Filing date: 2004-02-26
Publication date: 2005-08-31
Anticipated expiration: 2024-02-26
Also published as: GB2411375B; GB0404246D0

Abstract

A vibration reduction system and method for a pneumatic tool 1 for working a material, the tool being powered by an air supply 9, comprises at least one sensor 3 for producing a signal providing an indication of the vibration of the tool, a measurement system 5 to receive said signal and in response determine an optimum air supply for the tool to reduce vibration of the tool and an air supply control system 7 to adjust the air supply in response to a control signal produced by the measurement system.

Description

Vibration Reduction System This invention concerns a vibration reduction

system for a pneumatic tool.

Pneumatic cutting tools such as air hammers are conventionally used to break hard materials such as concrete and mortar. They often produce high levels of vibration when in operation. The frequency and magnitude of the vibrations are such that they may be harmful to the user of the pneumatic tool. Under current health and safety guidelines the use of the tool may be significantly limited if itproduces high-level vibrations of certain frequencies. These frequencies and magnitudes are described in BS EN ISO 5349-1:2001.

Obviously it is possible to reduce the level of vibration by simply reducing the air supply to the pneumatic tool. However, a simple reduction of air supply to the tool to reduce vibration decreases the efficiency of the cutting action. Consequently the cutting process takes longer thereby exposing the operator to a longer period of vibration and is therefore not an effective way of reducing exposure to vibration.

The relationship between the hardness of the material and the vibration of the tool is highly complex and depends primarily upon the construction of the tool. When air hammers are used against materials of different hardness the vibration of the tool changes by varying amounts in different axes depending on the nature of the surface being worked. By monitoring these vibrations it is possible to determine the hardness of the material being cut. Using this information the air supply to the tool can be adjusted to give optimum efficiency and minimum vibration levels for a given material. However, re-adjusting the air supply to a pneumatic tool whenever a different material is encountered is cumbersome and creates lengthy delays, as in a single cutting job the tool may have to cut several different materials.

It is an object of the present invention to provide an automatic system for reducing the level of vibration by optimizing the air supply to a pneumatic tool in dependence on the material being worked.

In accordance with a first aspect of the present invention there is provided a vibration reduction system for a pneumatic tool for working a material, the tool being powered by an air supply, comprising at least one sensor for producing a signal providing an indication of the vibration of the tool, a measurement system to receive said signal and determine an optimum air supply for the tool and an air supply control system to adjust the air supply in response to a control signal produced by the measurement system.

The at least one sensor may be mountable on the tool or wearable on the body of a tool operator.

Preferably, there is a plurality of sensors for measuring vibration in a plurality of orthogonal planes. Components of frequency and amplitude of the vibration may be measured.

The measurement system preferably compares the characteristics of the vibration with a set of known characteristics. These may comprise vibration and hardness characteristics for a selection of materials in a database. The measurement system may determine the hardness of the worked material and compare the hardness with known values of hardness for a selection of materials in a database. The database may comprise a look-up table, and contain information about the optimum air supply to be used for each material in the database. The measurement system advantageously determines which material in the database is most similar to the worked material and produces the control signal comprising information about the optimum air supply for that material.

The air supply control system may control the flow rate and or pressure of the air supply.

Advantageously, the air supply control system comprises at least one valve and at least one regulator.

In a further aspect, the invention provides a pneumatic tool when fitted with the inventive vibration reduction system.

According to a third aspect of the invention, there is provided a method of reducing vibration of a pneumatic tool, including the steps of measuring the vibration of the tool, using the measurements to determine an optimum air supply for the tool and adjusting the air supply to the tool to substantially conform to the optimum air supply.

S The step of measuring the vibration of the tool may comprise determining the components of vibration in a plurality of orthogonal planes, such as the components of frequency and amplitude of the vibration.

The hardness of a material being worked by the tool may be determined using the vibration 1 0 measurements.

The optimum air supply may preferably be determined by comparing characteristics of the vibration of the tool with a set of known characteristics, such as the vibration characteristics or hardness of known materials. Information may advantageously be stored about the optimum air supply for each known material. The known material that has characteristics most similar to the measured vibration may then be determined, and a control signal that comprises information relating to the optimum air supply for the known material is produced and the air supply adjusted to approximate the optimum air supply.

The invention will now be described by way of example with reference to the following figures, in which: Figure 1 shows a schematic view of an embodiment of the invention, and Figure 2 shows a schematic view of the air supply system of figure 1.

Figure 1 schematically shows a first preferred embodiment of the present invention. A pneumatic tool 1, shown as an air hammer, is of standard construction except that a collar 2 is mounted to it. Collar 2 in turn has sensors 3 mounted thereon, which are protected by the collar.

The sensors may be accelerometers, velocity or displacement measurement devices which sense the frequency and amplitude of the vibration of the tool, typically they may comprise piezo electric accelerometers. However, it is also possible to monitor the vibrations by monitoring the acoustic emissions of the tool. In this instance there are three sensors shown, which permit the sensing of vibration in three orthogonal axes x, y and z. Typically the sensors measure the vibration over a wide frequency band of about 0.5 to about 50000Hz. A cable 4 transfers vibration information from the sensors 3 to a measurement and control system, shown schematically as 5. The measurement and control system 5 is connected via a two-way control line 6 to an air supply control system 7. This regulates the air supply to the tool 1 via air supply line 8. The air is supplied by a compressed air source 9, which is typically a compressor, via a compressed air supply line 10.

The measurement and control system 5 is typically microprocessor-based, and as mentioned above receives vibration information from sensors 3, which is then processed by circuitry to provide frequency and amplitude data resolved in the x, y and z planes. These data are then processed by a comparator which checks the current pressure and flow rate of the air supply and uses this information to determine the material hardness from the vibration data and air supply data. The comparator then compares the material hardness and vibration characteristics with a database of known hardness and vibration characteristics for a selection of materials. The database may comprise a table, e.g. a look-up table. Also stored in the database are optimum air supply characteristics, i.e. flow rate and operating pressure, for each ofthe known materials. The comparator determines which of the known materials is most similar to the material being worked by the tool and hence the optimum air supply for the material. The comparator sends a control signal to the air supply control system 7 to supply air with these optimum characteristics.

Air supply control system 7 is shown in more detail in figure 2. Compressed air enters to air inlet manifold 1 1, which distributes air to a plurality of regulators 12 governed by solenoid valves 13.

The regulators are set to supply a range of pressures to the output, each regulator being set to a different pressure and supply rate. One solenoid valve 14 functions as a bleed valve to enable excess pressure to be vented from the system as the supply to the tool is requested. This avoids high transient vibration levels due to high impulsive flow rates. Air passing through each 3 0 regulator / valve route is collected by air outlet manifold 15 and then fed to the tool. A data line 16 is provided from the regulators 12 which passes flow supply information to the measurement and control system 5 for monitoring, while a control line 17 from the measurement and control system 5 is connected to the solenoid valves 13 to adjust the air supply as appropriate. The system shown enables a range of pressures and flow rates to be provided and changed very quickly. This means that as the tool encounters a different material, the correct solenoid valves are activated and the correct air supply is provided suff quickly, minimizing periods of high vibration. For example, the tool control system may typically change the air supply within about milliseconds such that as the tool encounters different materials its vibration level remains substantially constant.

In use, the tool supply line is brought up to operating pressure slowly to remove transient high level accelerations caused by stored elastic energy in the air supply lines.

In a second possible embodiment, the measurement and control system 5 does not require a database stored with known material characteristics. With this arrangement, the measurement and control system 5 acts to calculate the hardness of the material being worked and determines the optimum air pressure and flow-rate directly from the vibration measurements. A formula relating the acceleration along a particular axis to the hardness is required and the air supply calculated therefrom.

Although the invention has been described with reference to the embodiments above, there are many other modifications and alternatives possible within the scope ofthe claims. For example, instead of being mounted on collar 2, the sensors may be mounted directly onto vibrating surface of tool, or be worn by the user, for example on the wrist.

The sensors may communicate with the measurement and control microprocessor via a hardline or radio, optical, infra-red or sonic link for example. If a radio or sonic link is used for example, the flexibility of the system is increased and a user wearing the sensors will be able to leave the vicinity of the tool without disconnecting the sensors.

Claims

Claims l. A vibration reduction system for a pneumatic tool for working a

material, the tool being powered by an air supply, comprising at least one sensor for producing a signal providing an indication of the vibration of the tool, a measurement system to receive said signal and in response determine an optimum air supply for the tool to reduce vibration of the tool and an air supply control system to adjust the air supply in response to a control signal produced by the measurement system.
2. A vibration reduction system according to claim l wherein the at least one sensor is mountable on the tool.
3. A vibration reduction system according to claim 1 wherein the at least one sensor is wearable on the body of a tool operator.
4. A vibration reduction system according any preceding claim wherein there is a plurality of sensors for measuring vibration in a plurality of orthogonal planes.
5. A vibration reduction system according to any preceding claim wherein the measurement system determines components of frequency and amplitude of the vibration.
6. A vibration reduction system according to any preceding claim wherein the measurement system compares the characteristics of the vibration with a set of known characteristics.
7. A vibration reduction system according to claim 6 wherein the known characteristics comprise vibration and hardness characteristics for a selection of materials in a database.
8. A vibration reduction system according to either of claims 6 and 7 wherein the measurement system determines the hardness ofthe worked material and compares said hardness with known values of hardness for a selection of materials in a database.
9. A vibration reduction system according to either of claims 7 and 8 wherein the database comprises a look-up table.
l O. A vibration reduction system according to any of claims 7 to 9 wherein the database contains information about the optimum air supply to be used for each material in said database.
l I. A vibration reduction system according to claim lO wherein the measurement system determines which material in the database is most similar to the worked material and produces the control signal comprising information about the optimum air supply for that material.
12. A vibration reduction system according to any preceding claim wherein the air supply control system controls the flow rate of the air supply.
13. A vibration reduction system according to any preceding claim wherein the air supply control system controls the pressure of the air supply.
14. A vibration reduction system according any preceding claim wherein the air supply control system comprises at least one valve.
15. A vibration reduction system according to any preceding claim wherein the air supply control system comprises at least one regulator.
16. A pneumatic tool when fitted with the vibration reduction system according to any preceding claim.
17. A method of reducing vibration of a pneumatic tool, including the steps of measuring the vibration of the tool, using the measurements to determine an optimum air supply for the tool and adjusting the air supply to the tool to substantially conform to the optimum air supply.
18. A method according to claim 17 wherein the step of measuring the vibration of the tool comprises determining the components of vibration in a plurality of orthogonal planes.
19. A method according to either of claims 17 and 18 wherein the step of measuring the vibration of the tool comprises determining the components of frequency and amplitude of the vibration.
20. A method according to any of claims 17 to 19 including the step of determining the hardness of a material being worked by the tool using the vibration measurements.
21. A method according to any of claims 17 to 20 wherein the optimum air supply is determined by comparing characteristics of the vibration of the tool with a set of known I O characteristics.
22. A method according to claim 21 wherein the set of known characteristics comprises the vibration characteristics or hardness of known materials.
23. A method according to claim 22, wherein information is stored about the optimum air supply for each known material.
24. A method according to claim 23 wherein the step of comparing characteristics includes determining the known material that has characteristics most similar to the measured vibration.
25. A method according to claim 24 wherein the step of adjusting the air supply to the tool includes the step of producing a control signal that comprises information relating to the optimum air supply for the known material and adjusting the air supply to approximate the optimum air supply.
26. A vibration reduction system substantially as herein described with reference to the figures.
27. A method of reducing vibration substantially as herein described with reference to the figures.