WO2012158049A1

WO2012158049A1 - Ultrasonic device

Info

Publication number: WO2012158049A1
Application number: PCT/NZ2012/000069
Authority: WO
Inventors: Ross Douglas CLARKE; Shane Richard Leath; Robin HOLDSWORTH
Original assignee: Agresearch Limited
Priority date: 2011-05-19
Filing date: 2012-05-21
Publication date: 2012-11-22
Also published as: GB201319350D0; AU2012256467B2; NZ592935A; GB2504636B; GB2504636A; AU2012256467A1

Abstract

The present application relates to an ultrasonic device and associated method. The device includes a frequency generator configured to generate an oscillating signal having a predetermined frequency and power level. An ultrasonic transducer is configured to receive the oscillating signal and generate a mechanical vibration, wherein the frequency and amplitude of the mechanical vibration are controlled by the oscillating signal. A tool is configured to vibrate in response to the mechanical vibration, and at least one processor is configured to receive at least one operational characteristic relating to the vibration of the tool, and determine at least one property of material in contact with the tool using the operational characteristic in combination with predetermined values.

Description

ULTRASONIC DEVICE

STATEMENT OF CORRESPONDING APPLICATIONS

This application is based on the Provisional specification filed in relation to New Zealand Patent Application Number 592935, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an ultrasonic device. In particular, the present invention relates to an ultrasonic cutting device.

BACKGROUND ART

Ultrasonic techniques have been used in various industrial applications for decades, particular in the areas of grinding and cutting.

In the example of ultrasonic cutting, the basic means by which this is achieved is effectively universal. An ultrasonic generator is used to vibrate a blade, the resonant frequency of which is generally optimised for the material which it is intended to cut.

The ultrasonic vibration of the blade is intended to result in a very clean cut, and prevent residue sticking to the blade as it progresses through the material.

In surgical applications, ultrasonic vibration of the cutting implement may also have a cauterising or coagulating effect on tissue.

Some recent work in the area of ultrasonic cutting has focused on "tuning" or adjusting of the power and frequency of the cutting blade. This is usually in an attempt to improve the cutting ability of the ultrasonic blade in response to variations in the cutting conditions.

United States Patent No. 5101599 describes an ultrasonic cutting machine configured to determine the load on the tip of a tool and adjust the amplitude of vibration accordingly. This allows for more efficient chip disposal and compensates for changes in the sharpness of the tip.

Other processes using "autoresonance" methods are known. These implement feedback to monitor the frequency of the cutting blade and increase the power to the ultrasonic generator in order to maintain the vibration of the blade. These previous applications have focused on optimising the ultrasonic cutting of effectively homogeneous, or at least known, materials. However, there are many applications in which goods to be cut have multiple layers of differing materials. Furthermore, the thickness, composition and orientation of these layers may vary between items.

For example, when considering the processing of an animal carcass, the material to be cut may include pelt, muscle, fat, internal organs, or bone. The position, toughness, ratio and composition of these materials will vary between carcasses. Temperature and other environmental factors may also cause the material characteristics of these layers to vary.

Traditionally, oscillating toothed blades are used to cut the pelt free of the carcass. These blades can easily catch and tear the pelt or carcass, thereby reducing the value of these products. Further, the blades require sharpening every day. It is common to have a rotation of blades which are continually being removed and sharpened in order to maintain their cutting ability. The time and material costs reduce profitability of the process.

Further, known ultrasonic cutting control systems may be unable to compensate for such variability, potentially resulting in inefficient or ineffective operation of the machine, or damage to the carcass itself.

It would be advantageous if an ultrasonic cutting process could identify the material which was being cut, in order to optimise the cutting of said material or minimise the risk of damage to same.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only. DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided an ultrasonic device, including: a frequency generator configured to generate an oscillating signal having a

predetermined frequency and power level; an ultrasonic transducer configured to receive the oscillating signal and generate a mechanical vibration, wherein the frequency and amplitude of the mechanical vibration are controlled by the oscillating signal; a tool configured to vibrate in response to the mechanical vibration; characterised in that the ultrasonic device includes at least one processor configured to receive at least one operational characteristic relating to the vibration of the tool, and determine a property of material in contact with the tool using the operational characteristic in combination with predetermined values. According to another aspect of the present invention there is provided a method of operating an ultrasonic device, including the steps of: generating an oscillating signal having a predetermined frequency and power level; generating a mechanical vibration, wherein the frequency and amplitude of the mechanical vibration are controlled by the oscillating signal; vibrating a tool, wherein the tool is configured to vibrate in response to the mechanical vibration; measuring at least one operational characteristic relating to the vibration of the tool; and characterised by the step of: determining a property of material in contact with the tool using the operational characteristic in combination with predetermined values.

In a preferred embodiment the tool of the present invention includes a cutting blade. It should be appreciated that the blade may be configured to vibrate in a transverse, longitudinal, or rotational manner, depending on the desired functionality.

Reference may be made throughout the specification to the tool being a blade, and the ultrasonic device used in the processing of meat or carcasses. However, it should be appreciated that this is not intended to be limiting, and that other functions are envisaged. In particular, the present invention may be applied to the cutting of other heterogeneous material, such as fruits or vegetables, wood, or fish. As further examples, the present invention may be applied to the defleshing or shearing of a pelt, or de-hairing of a hide.

Further, it should be appreciated that the present invention is not intended to be limited to cutting, and that the tool may be configured to perform other operations, such as milling, sifting, , tamping, grinding or drilling.

It is envisaged that the tool may be connected to the ultrasonic transducer by way of a waveguide. It should be appreciated that the tool may be integral to the waveguide, also known as a tuning stem, or a separate component which may be attached by any suitable means known in the art.

Reference to a frequency generator should be understood to mean any electronic device which generates repeating, non-repeating, or arbitrary waveforms. In a preferred embodiment the frequency generator is configured to generate a substantially sinusoidal waveform, but it should be appreciated that other waveforms are envisaged - for example a sawtooth or square wave. Preferably the present invention includes a drive unit configured to step up the voltage or power level of the oscillating signal before being received by the ultrasonic transducer. It should be appreciated that this may be achieved by any means known in the art, such as a power amplifier and/or transformer and/or voltage amplifier. It should also be appreciated that the drive unit may be controlled by the processor to control characteristics of the oscillating signal. Reference to an ultrasonic transducer should be understood to mean any device which creates a mechanical vibration in response to an electrical signal, preferably in the ultrasonic range.

The ultrasonic transducer may generate the mechanical vibration in any suitable manner known in the art. For example, the ultrasonic transducer may employ a piezoelectric ceramic or quartz oscillator, or a magnetostrictive transducer.

Reference to operational characteristics relating to vibration of the tool should be understood to mean any characteristic by which the frequency, speed, wavelength and/or amplitude of the tool's vibration may be determined, directly or indirectly.

It should be appreciated that these parameters may not be actually measured or derived.

For example, it is envisaged that operational characteristics may be obtained by monitoring the electrical characteristics of the ultrasonic transducer, such as current, voltage, power, frequency, Q factor, magnitude, phase or any combination thereof. A person skilled in the art would appreciate that these characteristics will be influenced by the vibration of the tool and may be used to infer the mechanical characteristics of the vibration, or used directly in the determination of the material in contact with the tool. Alternatively, operational characteristics may be obtained by directly measuring mechanical characteristics of the tool's vibration, particularly displacement, frequency, velocity, or acceleration. Such measurement of mechanical characteristics may be obtained using any ultrasonic sensor known in the art, such as piezoelectric transducers, or laser based sensors. In a preferred embodiment, the measured operational characteristic may be used to determine additional parameters for use in determining the property of material in contact with the tool - for example the dielectric constant or phase constant.

Once the operational characteristics have been obtained, the processor may use these in comparison with predetermined values for to determine a property of the material. The predetermined values may be stored in look-up tables, or in any other suitable manner known in the art.

In a preferred embodiment determining the property of the material includes classifying the material. Reference to classifying the material should be understood to mean identification of what the material is, particularly in relation to differentiating between materials.

In the example of meat processing, it is envisaged that the device may be able to differentiate between pelt, muscle (pre rigor), meat (post rigor), bone, internal organs and fat. These materials may be classified within subclasses such as hot or chilled fat. It should be appreciated that this is not intended to be limiting, but is illustrative of the envisaged minimal sensitivity of the device.

However, it is envisaged that other properties may be determined. Using the example of meat processing, the property of the material may relate to water levels, pliability, or stiffness. This data may be used in assessing quality of the material, or determining an appropriate action for the processing of the material.

It should be appreciated that such a comparison may not require direct matching of the measured operational characteristics to the predetermined values. Rather, the processor may implement statistical comparison of the values, or any other suitable comparison known to a person skilled in the art.

For example, the processor may be configured to act as a proportional-integral- differential/derivative (PID) controller to cause the tool to vibrate at its harmonic frequency. The settings required to achieve this may be monitored by the processor, and if the settings are outside a preset range or threshold, the nature of the material may be inferred or an action taken.

Determination of the material in contact with the tool in conjunction with information relating to the travel or operation of the tool may be used in quality assessment or grading of the material. For example, the thickness of fat, or ratio of fat to meat in a particular cut may be used to grade the meat according to pre-established standards.

In a preferred embodiment, the processor is configured to control the frequency generator in response to the determination of the material in contact with the tool.

It should be appreciated that reference to automated control by the processor is not intended to be limiting. For example, the device may be configured to output a recommended configuration or action to an operator who may manually reconfigure the device accordingly or authorize the processor to carry out said action.

Once the material or property of the material in contact of the tool has been determined, it is envisaged that an optimal mode of operation for the tool will be implemented. The settings associated with the optimal mode of operation may be stored in look-up tables or obtained by any other suitable means known in the art.

It should be appreciated that determination of the property of the material may be inherent to the control of the device. For example, there may or may not be an intermediate step of identifying a particular property of the material using the operational characteristics prior to implementing the control associated with that property. The system may establish control parameters from the operational characteristics directly without such an intermediate step.

In one embodiment, the processor may control the power of the oscillating signal.

Alternatively, or in conjunction with the change in power level, the processor may control the frequency of the oscillating signal. In doing so, it is envisaged that the vibration of the tool will be closer to harmonic frequency when in contact with that particular material, enabling more efficient operation of the tool.

For example, where the present invention is used to process pitted fruit, there may be a mode for cutting the skin, a mode for cutting the flesh, and a mode for cutting the pit in which the power and/or frequency of the oscillating signal differs.

In another example, the present invention may be used to process fruit having a hard shell and soft flesh, such as pumpkin or squash. This may require two modes to optimise cutting through the two layers and reduce the extent to which the different materials stick to the blade.

In the example of meat processing, it is envisaged that the frequency of the oscillating signal ' may vary between 15 kilohertz (kHz) to 1 MHz in response to the material detected by the device.

It is envisaged that where a material is contacted which is unidentifiable, the settings required to vibrate the tool at its harmonic frequency may be stored by the processor. In doing so, the vibration of the tool may be optimised should the material be encountered again. Alternatively, the settings may be stored and used to identify the material using external sources.

In addition to allowing for optimal operation of the tool, information regarding the material in contact with the tool may be used in controlling the action of the tool in terms of orientation, direction, or depth. The action of the tool may be controlled by essentially any automated movement mechanism such as a CNC machine, robot, or any other suitable means known in the art.

For example, in the production of a frenched rack an automated process would need to identify the position of the rib bones and intercostal meat in order to perform the correct depth and angle of cuts required to meet the specifications provided by a customer. The present invention may be coupled with the control mechanism of such a process to aid in identification of the boundaries between the layers.

In the example of primal cutting, whereby a carcass is separated into sections from which designated cuts of meat are obtained, the invention may be implemented to determine the location of bones before making a cut. The blade could be touched to the spinal region of a carcass to determine whether it is over a bone or between bones (i.e. the vertebrae). If over bone, the blade may be shifted by a short distance before being applied to the carcass again. Once the blade is determined to be between vertebrae, the blade may be driven between the vertebrae and sever the spine.

In the further example of opening the abdominal cavity during evisceration of the carcass, the blade could be pushed through the abdominal muscles until the abdominal lining and/or viscera was detected and the knife stopped, thereby avoiding contamination of the meat from the intestinal contents.

Further, feedback from the blade could be used to guide a robot as a cut is made and terminate the cut upon reaching the sternum (bone).

In the example of boning, the blade could guide the robot and initiate/terminate cutting upon contact with expected materials (e.g. cartilage and/or bone) in order to bone complex shapes. This could be particularly useful in navigating the ball joint in a hind leg cut, or the removal of meat from around the shoulder.

It is also envisaged that the vibration of the tool may be controlled in order to cauterise, sear or seal the material. In the example of processing an animal carcass the tool may be used to limit liquid loss when cutting organs, or body parts such as the spinal cord.

The heat generated by the vibration could also be used to sterilize the cut face of a steak, or to sterilize the blade itself between cuts. Preferably, the processor is configured to stop operation of the ultrasonic device on determining human flesh in contact with the tool. This may be equally applicable to the detection of any material not intended to be in contact with the tool, such as foreign objects.

It is envisaged that this may have particular operation to surgical procedures. The present application may be applied to identify the passage of the surgical blade into material not intended to be contacted during a particular procedure, and switch off the cutting ability of the blade to prevent further damage.

It should be appreciated that this may be achieved in a number of ways, for example by turning off the frequency generator or ultrasonic generator, or control of the action of the tool to remove the tool from the immediate vicinity. In the example of a cutting machine, the cutting action of the blade may be reversed to remove pressure from the material.

In a preferred embodiment, the processor may also be configured to control at least one characteristic of the oscillating signal in order to determine a property of the material.

It is envisaged that altering a factor of the vibration while the tool is in contact with an identified material will allow for comparison of the change in operational characteristics to known values. As an example, the frequency of the signal may be shifted, and the power levels monitored to measure the effect.

It is envisaged that the processor may be configured to issue an alarm or notification on determination of a particular event. The event may be the determination of a foreign object or human in contact with the tool, determination that the composition of the material does not meet quality requirements, or any other desirable (or undesirable) factor.

The alarm may be in the form of a physical indicator in the vicinity of the device, or a control point. Alternatively, the alarm may be in the form of a flag set in software to alert an operator that a particular event has occurred, or trigger the implementation of further software instructions.

The processor may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices or controllers (PLDs, PLCs), field programmable gate arrays (FPGAs), computers, lap tops, controllers, micro-controllers, microprocessors, electronic devices, other electronic units (whether analogue of digital) designed to perform the functions described herein, or a combination thereof.

A software implementation may be implemented with modules (e.g., procedures, functions, and so on) that perform the steps of the method described herein. The software codes may be stored in a memory unit which may be within the processor or external to the processor. The steps of a method, process, or algorithm described in connection with the present invention may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The various steps or acts in a method or process may be performed in the order shown, or may be performed in another order. Additionally, one or more process or method steps may be omitted or one or more process or method steps may be added to the methods and processes. An additional step, block, or action may be added in the beginning, end, or intervening existing elements of the methods and processes.

The method and apparatus of the present invention may have a number of advantages over the prior art methods and devices, including: · improved efficiency and/or effectiveness of the operation of the device by adjusting to the presence of identified and/or unidentifiable materials;

• reduced downtime in a production environment due to the device's ability to adjust to a plurality of materials without external operator/senor input. For example, with a conveyor line for slicing pizza wherein the pizzas have mixed properties - cooked/uncooked, thin/thick crust, ingredients such as cheese or pepperoni - the present invention would not need reprogramming to account for different pliability between types of pizza;

• cost savings through reduction in wear on tools due to more efficient operation;

• improved quality control by assessment of material composition at the time of cutting, allowing for efficient decision making as to use or further processing of the material;

• automation of quality control by matching parameters used to process the material (and thereby material composition and thickness of the cut) to a carcass, and/or location or time; and

• increased safety by controlling operation of the device to account for the presence of foreign objects or human flesh in contact with the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: shows a schematic view of an ultrasonic device according to one embodiment of the present invention;

FIG. 2: is a flow diagram illustrating one method by which the present invention can be implemented, and

FIG. 3: is a graph illustrating the response of operational characteristics of an ultrasonic device according to one embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates an ultrasonic device (generally indicated by arrow 1 ) according to one aspect of the present invention.

The ultrasonic device 1 includes a processor 2, the operation of which will be described further below. The ultrasonic device 1 also includes a frequency generator 3 configured to generate an oscillating signal having a predetermined frequency and power level. The frequency generator 3 includes a signal generator 4 capable of generating an oscillating signal having a frequency between 15 kHz to 10 MHz. The signal is amplified by a voltage amplifier 5, for example up to 3000 V.

The ultrasonic device 1 also includes an ultrasonic transducer 6 in the form of a torus-shaped ceramic piezoelectric transducer. The ultrasonic transducer 6 is configured to receive the oscillating signal from the frequency generator 3 and generate a mechanical vibration, wherein the frequency and amplitude of the mechanical vibration are controlled by the oscillating signal.

A tuning stem 7 is connected to the ultrasonic transducer 6. The tuning stem 7 guides the mechanical vibration to a blade 8 connected to the end of the tuning stem 7. The blade 8 may be configured to vibrate in a transverse, longitudinal, or rotational manner depending on the application.

The processor may also receive a signal from a trigger (not illustrated) operated by an operator in order to activate the blade 8. In operation, the processor 2 is configured to receive operational characteristics in the form of feedback from the signal generator 4, and the voltage amplifier 5. Power output by the amplifier 5 is represented by P₀, the power at the load (i.e. transducer 6) by P_L and the phase of P₀ and P_L (Φι and Φ₂ respectively).

The processor 2 is configured to compare the operational characteristics (or variables calculated from these characteristics) with predetermined values stored in memory 9 and determine a material property of material in contact with the blade 8. This will be discussed in more detail with reference to FIG. 2 below. FIG. 2 is a flow diagram illustrating steps which could be taken in accordance with one embodiment of the present invention, using the ultrasonic device 1 described with reference to FIG. 1.

At step 201 the processor 2 retrieves standby parameters for the frequency generator 3 from memory 10. These standby parameters are such that feedback may be received without activating vibration of the blade 9 to the extent that it is likely to cut material on contact.

At step 202 the processor 2 controls the frequency generator to achieve the parameters previously set.

The signal from the signal generator 4 is amplified by amplifier 5 before being input to transducer 6. The blade 8 is vibrated accordingly.

At step 203 operational parameters in the form of power output (P₀), the power at the load (P_L) and the phase (Φ) at the amplifier 5 and load are received by the processor 2. Frequency of the signal output by the signal generator 4 is also determined. It should be appreciated that the signals indicative of these parameters may be filtered or otherwise preprocessed before being received by the processor 2.

At step 204, the operational parameters are used to calculate the variables which will be used in determining the material or material properties in contact with the blade 8.

In one exemplary embodiment, the variables include power loss and phase loss, where: power loss = P_L/Pol and

phase loss = Φ-ι -Φ₂.

Reference to phase loss should be understood to mean the change in phase due to a change in the impedance of an electrical system.

In step 205, the processor 2 determines whether the trigger has been activated by the operator. If not, the process loops back to step 201.

If the trigger has been activated, the processor determines at step 206 whether the blade 9 is in contact with material by comparing the calculated variables with known values for air. If not, the process loops back to step 201.

If the blade is determined to have contact with material, at step 207 the processor 2 compares the variables (e.g. power loss and phase shift) to a look up table which returns desirable parameter settings for the frequency generator 3, and loops back to step 202. For example, in the context of removing the pelt from an animal carcass, the processor 2 may determine that the blade is in contact with human flesh and cut power to the frequency generator 3. The operational characteristics and calculated variables are also recorded, and may be used to create a log of material or material properties which have come in contact with the blade 8.

FIG. 3 is a graph 300 illustrating the collection of operational characteristics using the device 1 of FIG. 1 and visualizes the comparisons which may be made between materials using the present invention.

Data 301 indicates the power output P₀ from amplifier 5, where P₀ has been held constant for the purpose of establishing baseline values. Data 302 is the power at the load (P_L), while data 303 is the Ratio Po P_- Trace 304 records the phase Φ of the signal on the output, while data 305 shows when the blade was activated or triggered. Period 306 indicates when the blade 8 was in contact with a pelt. It may be seen that there is a step in P₀ between the baseline and contact with the pelt, and again once the trigger is activated. Simultaneously, there is a drop off in Φ.

This contrasts with period 307 when the blade 8 is in contact with muscle; it may be seen that 0 rises significantly, along with an increase in P₀.

Moving to period 308, in which the blade 8 is in contact with the collagen connecting the pelt to the flesh, there is a drop off in P₀, combined with a steep decrease in Φ.

It may be seen from this raw data that different materials have quite different responses which may be used to determine their presence and subsequently control the operating parameters in response to the presence of that material - for example setting optimal parameters for cutting. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims

WHAT WE CLAIM IS:

1. An ultrasonic device, including:

a frequency generator configured to generate an oscillating signal having a

predetermined frequency and power level; an ultrasonic transducer configured to receive the oscillating signal and generate a mechanical vibration, wherein the frequency and amplitude of the mechanical vibration are controlled by the oscillating signal;

a tool configured to vibrate in response to the mechanical vibration;

characterised in that the ultrasonic device includes at least one processor configured to receive at least one operational characteristic relating to the vibration of the tool, and determine at least one property of material in contact with the tool using the operational characteristic in combination with predetermined values.

2. An ultrasonic device as claimed in claim 1 , wherein the operational characteristic is used to determine additional parameters for use in determining the property of material in contact with the tool.

3. An ultrasonic device as claimed in either claim 1 or claim 2, wherein the processor is configured to classify the material in contact with the tool.

4. An ultrasonic device as claimed in any one of claims 1 to 3, wherein the processor is configured to control the tool according to the determined property of the material.

5. An ultrasonic device as claimed in claim 4, wherein the processor is configured to stop operation of the ultrasonic device on determining a particular material is in contact with the tool.

6. An ultrasonic device as claimed in any one of claims 1 to 5, wherein the processor is configured to control at least one characteristic of the oscillating signal in order to determine a property of the material.

7. An ultrasonic device as claimed in claim 6, wherein the processor is configured to receive a operating characteristic at a first setting of the characteristic of the oscillating signal, and the operating characteristic at a second setting of the oscillating signal, and use the change in the operational characteristic to determine the property of the material.

8. An ultrasonic device as claimed in any one of claims 1 to 7, wherein the processor is configured to record settings of the frequency generator required to vibrate the tool at its harmonic frequency when the property of the material cannot be determined.

9. An ultrasonic device as claimed in any one of claims 1 to 8, wherein the processor is configured to receive information relating to the travel of the tool and use this in conjunction with the property of the material to grade the material.

10. An ultrasonic device as claimed in any one of claims 1 to 9, wherein the tool includes a cutting blade.

11. An ultrasonic device as claimed in any one of claims 1 to 10, wherein the tool is connected to the ultrasonic transducer by way of a waveguide.

12. A method of operating an ultrasonic device, including the steps of:

generating an oscillating signal having a predetermined frequency and power level; generating a mechanical vibration, wherein the frequency and amplitude of the mechanical vibration are controlled by the oscillating signal;

vibrating a tool, wherein the tool is configured to vibrate in response to the mechanical vibration;

measuring at least one operational characteristic relating to the vibration of the tool; and characterised by the step of:

determining a property of material in contact with the tool using the operational characteristic in combination with predetermined values.

13. A method as claimed in claim 12, including the step of determining additional parameters for use in determining the property of material in contact with the tool based on the operational characteristic.

14. A method as claimed in either claim 12 or claim 13, wherein determining the property of the material includes classifying the material.

15. A method as claimed in any one of claims 12 to 14, including the step of controlling operation of the tool according to the determined property of the material.

16. A method as claimed in claim 15, wherein controlling operation of the tool includes stopping operation of the ultrasonic device on determining a particular material is in contact with the tool.

17. A method as claimed in any one of claims 12 to 16, including the step of controlling at least one characteristic of the oscillating signal in order to determine a property of the material.

18. A method as claimed in claim 17, including the steps of:

receiving a operating characteristic at a first setting of the characteristic of the oscillating signal;

receiving the operating characteristic at a second setting of the oscillating signal; and using the change in the operational characteristic to determine the property of the material.

19. A method as claimed in any one of claims 12 to 18, including the step of to recording settings of the frequency generator required to vibrate the tool at its harmonic frequency when the property of the material cannot be determined.

20. A method as claimed in any one of claims 12 to 19, including the steps of:

receiving information relating to the travel of the tool; and

using this information in conjunction with the property of the material to grade the material.