A surgical instrument control method and system based on adaptive life curve control (ALCC)

Abstract

The present application relates to surgical instrument control technical field, provide a kind of based on adaptive life curve ALCC surgical instrument control method, comprising: S1: the used life of surgical instrument is obtained, according to the used life from adaptive life curve ALCC find corresponding existing plastic deformation, according to existing plastic deformation calculation the damage of each axis;S2: when damage condition does not reach the scrapping standard, using surgical instrument carries out operation, obtains the stress information of each axis of surgical instrument in the operation process, according to stress information, the plastic deformation of each axis of surgical instrument working section is calculated, according to existing plastic deformation and working section plastic deformation, the position instruction of each axis of surgical instrument is compensated in real time;S3: according to working section plastic deformation, update existing plastic deformation, and according to adaptive life curve ALCC, update the used life.Adaptive compensation plastic deformation influence, both guarantee surgical instrument movement control precision in each operation, and increase the service life of surgical instrument.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of surgical instrument control, and in particular to a surgical instrument control method and system based on an adaptive life curve control method (ALCC). BACKGROUND

[0002] Surgical robots are advanced medical devices operated by medical professionals for various types of surgery. These robotic systems usually include mechanical arms, control consoles, vision systems, and surgical tools. They are designed to provide more precise, stable, and minimally invasive surgical procedures.

[0003] Here are some features and advantages of surgical robots:

[0004] (1) Precision: Surgical robots can provide highly precise operations, as their mechanical arms have great flexibility and fine motion control. This allows doctors to perform more accurate operations during surgery.

[0005] (2) Stability: Robotic systems usually have a stable platform that can reduce hand tremors and movements during surgery, thereby improving the stability of the surgery.

[0006] (3) Three-dimensional vision: Surgical robot systems are usually equipped with high-resolution three-dimensional cameras and microscopes, allowing doctors to clearly observe the surgical area and help them locate and operate more accurately.

[0007] (4) Minimally invasive surgery: Surgical robots can perform surgery through smaller incisions or through natural orifices in the body, reducing trauma to the patient and recovery time.

[0008] (5) Teleoperation and control console: Doctors can teleoperate the robot through a control console while observing high-definition visual feedback. This allows doctors to perform surgery in a comfortable location.

[0009] Surgical instruments, as the end execution unit of surgical robots, directly contact the human body and perform surgical operations in a complex in-vivo environment, requiring high precision in motion control.

[0010] Surgical instruments are usually driven by wire, and before and after surgery, surgical instruments need to undergo sterilization and disinfection. During the surgery, the steel wire repeatedly stretches and contracts, constantly undergoing elastic deformation. When stretched to a certain extent, these operations will cause the surgical instrument to undergo a certain degree of irreversible plastic deformation, affecting the precision of motion control. As the number of uses increases, the plastic deformation of the surgical instrument accumulates, and when the original control algorithm cannot meet the high precision requirements of motion control, the instrument reaches its service life and is scrapped.

[0011] Therefore, it is necessary to carry out plastic deformation based on surgical instruments, calculate the used life, and adaptively compensate the influence of plastic deformation, so as to ensure the accuracy of motion control and further improve the service life of the instruments. SUMMARY

[0012] In view of the above problems, the purpose of the present application is to provide a surgical instrument control method and system based on adaptive life curve ALCC, which calculates the used life based on the plastic deformation of surgical instruments, adaptively compensates the influence of plastic deformation, ensures the accuracy of surgical instrument motion control in each operation, and increases the service life of surgical instruments.

[0013] The above application purpose of the present application is realized by the following technical scheme:

[0014] A surgical instrument control method based on adaptive life curve ALCC, comprising the following steps:

[0015] S1: After the surgical instrument is installed on the surgical equipment, the used life of the surgical instrument is obtained from the surgical instrument information, and the existing plastic deformation amount of the surgical instrument corresponding to the used life is found from the adaptive life curve ALCC, and the damage condition of each shaft of the surgical instrument is calculated according to the existing plastic deformation amount;

[0016] S2: When the damage condition does not reach the scrap standard of the surgical instrument, the surgical instrument is used for operation, the stress information of each shaft of the surgical instrument is obtained during the operation, the plastic deformation amount of the working section of each shaft of the surgical instrument is calculated according to the stress information, and the position command of each shaft of the surgical instrument is compensated in real time according to the existing plastic deformation amount and the working section plastic deformation amount;

[0017] S3: The existing plastic deformation amount is updated according to the working section plastic deformation amount, and the used life is updated according to the adaptive life curve ALCC.

[0018] Further, before step S1, it further comprises: drawing the adaptive life curve ALCC in advance, specifically:

[0019] A large amount of experimental data or running data during actual experiments on the surgical instrument or during actual use is collected as a data set, and the used life of the surgical instrument under different existing plastic deformation amounts in the data set is obtained;

[0020] The relationship between the existing plastic deformation amount and the used life of the surgical instrument in the data set is calculated by using a preset algorithm, the adaptive life curve ALCC is established with the existing plastic deformation amount as the horizontal axis and the used life as the vertical axis;

[0021] The preset algorithm is used to continuously optimize and adjust the adaptive life curve ALCC according to the relationship between the existing plastic deformation amount and the used life of the surgical instrument in actual use.

[0022] Further, in step S1, the damage condition of each shaft of the surgical instrument is calculated according to the existing plastic deformation amount, specifically:

[0023] An elastic-plastic damage constitutive model of the material of each shaft of the surgical instrument is established, and a damage variable corresponding to the existing plastic deformation amount for judging the damage condition is calculated according to the elastic-plastic damage constitutive model.

[0024] Further, the elastic-plastic damage constitutive model is calculated by the following formula:

[0025]

[0026] wherein, is the damage variable, is a critical value of the damage variable, is the existing plastic deformation amount, is a strain threshold value of damage under tension of each shaft of the surgical instrument, is a fracture strain value under tension to cause damage;

[0027] The critical value of the damage variable has the following specific forms:

[0028]

[0029] wherein, and are material hardening coefficients, is a material parameter, is a Poisson's ratio, is an elastic modulus, is a norm equivalent stress, is an average stress, is a damage strain value, is a fracture strain value.

[0030] Further, in step S2, it also includes: judging whether the damage condition reaches the scrapping standard of the surgical instrument, specifically:

[0031] A preset limit value of the damage variable of the surgical instrument is set ;

[0032] If the damage variable If the preset limit value is not reached, the surgical instrument is used for surgery, and if the damage variable If the preset limit value is reached, the surgical instrument is scrapped.

[0033] Further, in step S2, the force information of each shaft of the surgical instrument is acquired during surgery, and the plastic deformation amount of the working section of each shaft of the surgical instrument is calculated according to the force information, specifically:

[0034]

[0035] wherein, and is the material hardening coefficient, is the force information, is the damage variable corresponding to the existing plastic deformation amount for judging the damage condition.

[0036] Further, in step S2, the position command of each shaft of the surgical instrument is compensated in real time according to the existing plastic deformation amount and the working section plastic deformation amount, specifically:

[0037] +

[0038] wherein, is the current real-time position command, is the real-time position command of the original undamaged new instrument, is the existing plastic deformation amount, is the working section plastic deformation amount.

[0039] Further, in step S3, the existing plastic deformation amount is updated according to the working section plastic deformation amount, specifically:

[0040] The working section plastic deformation amount is added to the existing plastic deformation amount, and the specific formula is:

[0041]

[0042] wherein, is the existing plastic deformation amount, is the working section plastic deformation amount;

[0043] Meanwhile, the elastoplastic damage constitutive model is used to update the damage variable corresponding to the existing plastic deformation amount for judging the damage condition.

[0044] An adaptive life curve based (ALCC) surgical instrument control system for performing the adaptive life curve based (ALCC) surgical instrument control method as described above, comprising:

[0045] a damage condition calculation module configured to, after the surgical instrument is installed on the surgical device, obtain a used life of the surgical instrument from the surgical instrument information, and find a corresponding existing plastic deformation amount of the surgical instrument from the adaptive life curve (ALCC) according to the used life, and calculate a damage condition of each shaft of the surgical instrument according to the existing plastic deformation amount;

[0046] a position instruction compensation module configured to, when the damage condition does not reach the retirement standard of the surgical instrument, use the surgical instrument to perform surgery, obtain stress information of each shaft of the surgical instrument during the surgery, calculate a working section plastic deformation amount of each shaft of the surgical instrument according to the stress information, and compensate a position instruction of each shaft of the surgical instrument in real time according to the existing plastic deformation amount and the working section plastic deformation amount;

[0047] a data updating module configured to update the existing plastic deformation amount according to the working section plastic deformation amount, and update the used life according to the adaptive life curve (ALCC).

[0048] A computer device comprising a memory and one or more processors, the memory storing computer code, the computer code being executed by the one or more processors to cause the one or more processors to perform the method as described above.

[0049] A computer readable storage medium storing computer code, the computer code being executed to perform the method as described above.

[0050] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0051] By providing a surgical instrument control method based on an adaptive life curve ALCC, comprising: S1: after the surgical instrument is installed on the surgical device, the used life of the surgical instrument is obtained from the surgical instrument information, and the corresponding existing plastic deformation amount of the surgical instrument is found from the adaptive life curve ALCC according to the used life, and the damage condition of each shaft of the surgical instrument is calculated according to the existing plastic deformation amount; S2: when the damage condition does not reach the scrap standard of the surgical instrument, the surgical instrument is used for surgery, the stress information of each shaft of the surgical instrument is obtained during the surgery, the working section plastic deformation amount of each shaft of the surgical instrument is calculated according to the stress information, and the position command of each shaft of the surgical instrument is compensated in real time according to the existing plastic deformation amount and the working section plastic deformation amount; S3: the existing plastic deformation amount is updated according to the working section plastic deformation amount, and the used life is updated according to the adaptive life curve ALCC. The above technical scheme is based on the stress information, tensile state and real-time calculation of the elastic-plastic deformation amount of the steel wire rope, based on the elastic-plastic deformation amount of the steel wire rope, the used life of the surgical instrument is inferred, based on the used life of the instrument, the influence of plastic deformation is adaptively compensated, and the motion control precision of the surgical instrument is ensured.

[0052] By adaptively compensating the influence of plastic deformation on the surgical instrument, the service life of the surgical instrument can be increased. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 The overall flowchart of the surgical instrument control method based on the adaptive life curve ALCC of the application is shown in the figure;

[0054] Figure 2 The detailed flowchart of the surgical instrument control method based on the adaptive life curve ALCC of the application is shown in the figure;

[0055] Figure 3 The schematic diagram of the adaptive life curve ALCC of the application is shown in the figure;

[0056] Figure 4 The overall structure diagram of the surgical instrument control system based on the adaptive life curve ALCC of the application is shown in the figure. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0058] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It is further understood that the terms "comprising," "including," "containing," and "having" and the like, when used in the specification, specify the presence of stated features, integers, steps, operations, elements, and / or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0059] First embodiment

[0060] As shown in Figure 1 and 2 , the embodiment provides a surgical instrument control method based on an adaptive life curve ALCC, comprising the following steps:

[0061] S1: After the surgical instrument is installed on the surgical device, the used life of the surgical instrument is obtained from the surgical instrument information, and the existing plastic deformation amount of the surgical instrument corresponding to the used life is found from the adaptive life curve ALCC according to the used life, and the damage condition of each shaft of the surgical instrument is calculated according to the existing plastic deformation amount.

[0062] Specifically, when the target surgical instrument is installed on the surgical device, the used life of the current surgical instrument needs to be obtained from the saved surgical instrument information, and the existing plastic deformation amount of the surgical instrument corresponding to the used life of the surgical instrument is found from the adaptive life curve ALCC according to the used life of the surgical instrument , and the damage condition of each shaft of the surgical instrument is calculated according to the existing plastic deformation amount, that is, the damage variable of the surgical instrument is calculated In the embodiment, each shaft of the surgical instrument is specifically a shaft formed of a steel wire rope material.

[0063] Before step S1, it also includes: drawing the adaptive life curve ALCC in advance, which is specifically:

[0064] (1) Collect a large amount of experimental data or running data during actual experiments on the surgical instrument or during actual use as a data set, and obtain the used life of the surgical instrument under different existing plastic deformation amounts in the data set.

[0065] (2) The relationship between the existing plastic deformation amount and the used life of the surgical instrument in the data set is calculated by using a preset algorithm, and the adaptive life curve ALCC as shown in Figure 3 is established with the existing plastic deformation amount as the horizontal axis and the used life as the vertical axis.

[0066] The preset algorithm is not limited in the embodiment, and only needs to simulate the relationship between the existing plastic deformation and the service life according to a large amount of data sets, to form a curve with the existing plastic deformation as the horizontal axis and the service life as the vertical axis. For example, the nonlinear least square method can be used to fit the data of the existing plastic deformation and the service life.

[0067] (3) The adaptive life curve ALCC is continuously optimized and adjusted according to the relationship between the existing plastic deformation and the service life of the surgical instrument in actual use by the preset algorithm.

[0068] In step S1, the damage condition of each shaft of the surgical instrument is calculated according to the existing plastic deformation, specifically: an elastic-plastic damage constitutive model of the material of each shaft of the surgical instrument is established, and a damage variable for judging the damage condition corresponding to the existing plastic deformation is calculated according to the elastic-plastic damage constitutive model.

[0069] In the present application, the damage variable is defined as the ratio of the bearing area of the damaged material to the bearing area of the material before damage, that is

[0070]

[0071] When is the undamaged state of the material, represents the complete fracture of the material, and 0-1 corresponds to different degrees of damage state. The following formula of the elastic-plastic damage constitutive model is used for calculation:

[0072]

[0073] wherein, is the damage variable, is the critical value of the damage variable, is the existing plastic deformation, is the strain threshold value of damage of each shaft of the surgical instrument under tension, is the fracture strain value of damage under tension.

[0074] The specific form of the critical value of the damage variable is:

[0075]

[0076] wherein, and are material hardening coefficients, is a material parameter,​ Poisson's ratio, For elastic modulus, For paradigm equivalent force, For average stress, This represents the damage strain value. This represents the fracture strain value.

[0077] S2: When the damage does not reach the scrapping standard of the surgical instrument, the surgical instrument is used to perform surgery. During the surgery, the force information of each axis of the surgical instrument is obtained. Based on the force information, the plastic deformation of the working section of each axis of the surgical instrument is calculated. Based on the existing plastic deformation and the plastic deformation of the working section, the position command of each axis of the surgical instrument is compensated in real time.

[0078] Specifically, in this embodiment, before performing the surgery, it is first necessary to determine whether the damage meets the scrapping standard of the surgical instruments, specifically as follows:

[0079] Set a preset limit value for the damage variable of the surgical instrument. In this embodiment, Set it to 0.5.

[0080] If the damage variable If the preset limit value is not reached, the surgical instrument is used to perform the surgery; if the damage variable... When the preset limit value is reached, the surgical instrument is scrapped.

[0081] In step S2, during the operation, the working status of the steel wire rope of each axis of the surgical instrument is obtained in real time based on the encoder information and current information of each drive motor of the surgical instrument, that is, the working section of the steel wire rope and the force information of each axis of the surgical instrument are obtained. Based on the force information, the plastic deformation of the working section of each axis of the surgical instrument is calculated in real time, specifically:

[0082]

[0083] in, and The material hardening coefficient, The force information, The damage variable is used to determine the damage condition, corresponding to the existing amount of plastic deformation.

[0084] In step S2, the position commands of each axis of the surgical instrument are compensated in real time based on the existing plastic deformation and the plastic deformation of the working section, specifically as follows:

[0085] +

[0086] wherein, is a current real-time position instruction, is a real-time position instruction of an original undamaged new instrument, is the existing plastic deformation amount, is the working segment plastic deformation amount.

[0087] S3: updating the existing plastic deformation amount according to the working segment plastic deformation amount, and updating the used life according to the existing plastic deformation amount and the adaptive life curve ALCC.

[0088] updating the existing plastic deformation amount according to the working segment plastic deformation amount, specifically:

[0089] accumulating the working segment plastic deformation amount to the existing plastic deformation amount, and the specific formula is:

[0090]

[0091] wherein, is the existing plastic deformation amount, is the working segment plastic deformation amount;

[0092] simultaneously updating the damage variable used for judging the damage condition corresponding to the current existing plastic deformation amount by using the elastic-plastic damage constitutive model, that is,

[0093]

[0094] wherein, is the damage variable, is a critical value of the damage variable, is the existing plastic deformation amount, is a strain threshold value of damage generated under stretching of each shaft of the surgical instrument, is a fracture strain value of damage generated under stretching.

[0095] Second embodiment

[0096] As shown in Figure 4 the embodiment provides a surgical instrument control system based on an adaptive life curve ALCC for performing a surgical instrument control method based on an adaptive life curve ALCC as in the first embodiment, comprising:

[0097] The damage condition calculation module 1 is used to obtain the used life of the surgical instrument from the surgical instrument information after the surgical instrument is installed on the surgical device, and find the existing plastic deformation amount of the surgical instrument from the adaptive life curve ALCC according to the used life, and calculate the damage condition of each shaft of the surgical instrument according to the existing plastic deformation amount.

[0098] The position instruction compensation module 2 is used to perform surgery by using the surgical instrument when the damage condition does not reach the retirement standard of the surgical instrument, obtain the force information of each shaft of the surgical instrument during the surgery, calculate the plastic deformation amount of the working section of each shaft of the surgical instrument according to the force information, and compensate the position instruction of each shaft of the surgical instrument in real time according to the existing plastic deformation amount and the plastic deformation amount of the working section.

[0099] The data updating module 3 is used to update the existing plastic deformation amount according to the plastic deformation amount of the working section, and update the used life according to the adaptive life curve ALCC.

[0100] A computer readable storage medium stores computer codes, when the computer codes are executed, the above method is executed. Those skilled in the art can understand that all or part of the steps in the above method can be completed by programs instructing related hardware, and the programs can be stored in a computer readable storage medium, and the storage medium can include a read only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0101] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above embodiment. Any technical solution falling within the concept of the present application shall be considered as the protection scope of the present application. It should be noted that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements shall also be considered as the protection scope of the present application.

[0102] The technical features of the above embodiments can be combined arbitrarily. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, they shall be considered as the scope of the present application.

[0103] It should be noted that the above embodiments can be freely combined as needed. The above only describes the preferred embodiments of the present application, and it should be pointed out that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered as the protection scope of the present application.

Claims

1. A surgical instrument control method based on adaptive life curve control (ALCC), characterized by, The method comprises the following steps: S1: After the surgical instrument is installed on the surgical device, the used life of the surgical instrument is obtained from the surgical instrument information, and the existing plastic deformation amount of the surgical instrument is found from the adaptive life curve ALCC according to the used life, and the damage condition of each shaft of the surgical instrument is calculated according to the existing plastic deformation amount; S2: When the damage condition does not reach the scrap standard of the surgical instrument, the surgical instrument is used for surgery, the stress information of each shaft of the surgical instrument is obtained during the surgery, the working section plastic deformation amount of each shaft of the surgical instrument is calculated according to the stress information, and the position instruction of each shaft of the surgical instrument is compensated in real time according to the existing plastic deformation amount and the working section plastic deformation amount; S3: The existing plastic deformation amount is updated according to the working section plastic deformation amount, and the used life is updated according to the adaptive life curve ALCC; In step S1, the damage condition of each shaft of the surgical instrument is calculated according to the existing plastic deformation amount, specifically: an elastic-plastic damage constitutive model of the material of each shaft of the surgical instrument is established, and a damage variable for judging the damage condition corresponding to the current existing plastic deformation amount is calculated according to the elastic-plastic damage constitutive model; The elastic-plastic damage constitutive model is calculated by the following formula: wherein, is the damage variable, is the critical value of the damage variable, is the existing plastic deformation, is the strain threshold value of damage generated under the stretching of each shaft of the surgical instrument, is the fracture strain value of damage generated under stretching. Critical values of the impairment variable The specific manifestations are: wherein, and is a material hardening coefficient, is a material parameter, is a Poisson's ratio, is an elastic modulus, is a norm equivalent stress, is an average stress, is a damage strain value, is a fracture strain value.

2. The method of adaptive life curve control (ALCC) based surgical instrument control of claim 1, wherein, Before step S1, it also includes: drawing the adaptive life curve ALCC in advance, specifically: A large amount of experimental data or operation data during actual experiments on the surgical instrument is collected as a data set, and the used life of the surgical instrument under different existing plastic deformation amounts in the data set is obtained; The relationship between the existing plastic deformation amount and the used life of the surgical instrument in the data set is calculated by using a preset algorithm, and the adaptive life curve ALCC is established with the existing plastic deformation amount as the horizontal axis and the used life as the vertical axis; The adaptive life curve ALCC is continuously optimized and adjusted by using the preset algorithm according to the relationship between the existing plastic deformation amount and the used life of the surgical instrument during actual use.

3. The surgical instrument control method based on adaptive life curve control (ALCC) according to claim 1, characterized in that, In step S2, it also includes: judging whether the damage condition reaches the scrap standard of the surgical instrument, specifically: setting a preset limit value of the lesion variable of the surgical instrument ; If the damage variable If the preset limit value is not reached, the surgical instrument is used to perform the surgery; if the damage variable... When the preset limit value is reached, the surgical instrument is scrapped.

4. The surgical instrument control method based on adaptive life curve control (ALCC) according to claim 1, characterized in that, In step S2, the stress information of each shaft of the surgical instrument is obtained during the surgery, and the working section plastic deformation amount of each shaft of the surgical instrument is calculated according to the stress information, specifically: wherein, and is a material hardening coefficient, is the force information, is the damage variable corresponding to the current existing plastic deformation amount for judging the damage condition.

5. The method of adaptive life curve control (ALCC) based surgical instrument control of claim 4, wherein, In step S2, the position instruction of each shaft of the surgical instrument is compensated in real time according to the existing plastic deformation amount and the working section plastic deformation amount, specifically: + wherein, is a current real-time position command, is a real-time position command for a pristine, undamaged new instrument, is the existing amount of plastic deformation, is the plastic deformation of the workpiece.

6. The surgical instrument control method based on adaptive life curve control (ALCC) of claim 1, wherein, In step S3, the existing plastic deformation amount is updated according to the working section plastic deformation amount, specifically: The working section plastic deformation amount is added to the existing plastic deformation amount, and the specific formula is: wherein, is the amount of plastic deformation of the workpiece, is the amount of plastic deformation of the workpiece; The elastic-plastic damage constitutive model is used to update the damage variable for judging the damage condition corresponding to the current existing plastic deformation amount.

7. An adaptive life curve control (ALCC) based surgical instrument control system for performing the adaptive life curve control (ALCC) based surgical instrument control method according to any one of claims 1 to 6, characterized by It comprises: The damage condition calculation module is configured to, after the surgical instrument is installed on the surgical device, acquire a used life of the surgical instrument from the surgical instrument information, find a corresponding existing plastic deformation of the surgical instrument from the adaptive life curve ALCC according to the used life, and calculate the damage condition of each shaft of the surgical instrument according to the existing plastic deformation. The position instruction compensation module is configured to, when the damage condition does not reach the retirement standard of the surgical instrument, perform surgery by using the surgical instrument, acquire stress information of each shaft of the surgical instrument during the surgery, calculate a working section plastic deformation of each shaft of the surgical instrument according to the stress information, and compensate a position instruction of each shaft of the surgical instrument in real time according to the existing plastic deformation and the working section plastic deformation. The data updating module is configured to update the existing plastic deformation according to the working section plastic deformation, and update the used life according to the adaptive life curve ALCC. 8.A computer readable storage medium, the computer readable storage medium storing computer code which, when executed, performs the method of any one of claims 1 to 6.

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