CONTROL DEVICE AND METHOD FOR SETTING UPPER AND LOWER LIMIT CURVES FOR ONE OR MORE TOOLS CONFIGURED TO INSTALL FASTENERS - Patent application

Abstract

A controller for one or more tools configured to set fasteners in a production process is provided, the controller obtaining a set of trace data (15) relating to a plurality of test fastener setting operations performed by at least one of the one or more tools in a production setup process, and determining from the set of trace data a maximum and minimum value indicative of setting force (T) for each of a plurality of values ​​indicative of displacement or time (α). max , T min ) or its derivative, calculates first and second polynomials based thereon, and sets upper and lower limit curves (11, 12) based on the first and second polynomials. Then, in the production process, the control device determines that the fastener installation operation is not acceptable (NOK) if the trace data (16) exceeds the upper and lower limit curves. This provides a balanced trade-off between the leniency / strictness of the limit values ​​and improves the detection accuracy of NOK operations.

Description

[Technical Field]

[0001] The present invention relates generally to the field of controls for one or more tools configured to install fasteners in a manufacturing process. In particular, the present invention relates to such controls capable of setting limit curves for detecting non-okay (NOK) fastener installation operations. [Background technology]

[0002] In industrial assembly plants, tools are used to install fasteners into objects in order to join different pieces of material together during the production process. Examples of such tools are clamping tools for installing threaded fasteners (such as screws and nuts) and riveting tools for installing rivets.

[0003] In such production processes, it is important to detect fastener installation operations performed by such tools that do not meet the desired quality standards. Such operations are usually referred to as rejected, non-compliant, or non-OK fastener installation operations. To name a few, such non-compliant fastener installation operations are operations involving fasteners with incorrect dimensions, fasteners with incorrect thread coating, fasteners that are skewed during insertion, or operations that exhibit so-called stick-slip (chatter). The cause of stick-slip is a complex dynamic phenomenon involving many physical parameters, which results in the joint starting to behave like an oscillating spring, resulting in torque values ​​oscillating at high frequencies.

[0004] To detect such NOK fastener installation operations, trace data from the tool operation is collected. Typically, such trace data includes values ​​representing installation force (such as torque or clamping force) against values ​​representing displacement (such as angle) or time, and can be displayed graphically.

[0005] Furthermore, these limits are typically manually set by production engineers during a setup process before production begins. Later in production, it is detected whether the trace data for an operation exceeds these limits. If so, the fastener installation operation is classified as a non-OK operation and typically recorded as such in the production control system and displayed to the tool operator. The operator must then retry the fastener installation to obtain a passing result.

[0006] A drawback of current solutions for setting such limits is that they generally require manual setting of the limits. Furthermore, it can be difficult to balance the trade-off between setting limits that are generous enough to avoid false NOK detections and strict enough to avoid missing activities that would otherwise be detected as NOK. Failing to find this balance reduces the accuracy of the NOK activity detection process. Summary of the Invention [Problem to be solved by the invention]

[0007] It would be advantageous to provide a control system and method that overcomes or at least mitigates the above-mentioned drawbacks. In particular, it would be desirable to provide a control system and method that facilitates setting limits for purposes of detecting NOK fastener installation operations. It would also be desirable to enable more accurate detection of NOK fastener installation operations. [Means for solving the problem]

[0008] In order to better address one or more of these problems, a control device and a method are provided having the features defined in the independent claims. Preferred embodiments are defined in the dependent claims.

[0009] Thus, according to a first aspect, there is provided a controller for one or more tools configured to install fasteners in a production process, the controller comprising: obtaining a set of trace data for a plurality of test fastener installation operations performed on a joint type by at least one of the one or more tools, the trace data including, for each fastener installation operation, a value indicative of installation force with respect to a value indicative of displacement or time, or a derivative thereof; deriving a maximum value or its derivative indicative of the attachment force for each of a plurality of values ​​indicative of displacement or time from the set of trace data, and calculating a first polynomial based on these maximum values; deriving a minimum value or its derivative indicative of the attachment force for each of a plurality of values ​​indicative of displacement or time from the set of trace data, and calculating a second polynomial based on these minimum values; setting an upper limit curve based on the first polynomial; setting a lower limit curve based on the second polynomial; It is structured as follows: The control device, in the production process following the production setting process, The method is further configured to determine that a fastener setting operation performed by any one of the one or more tools is not acceptable (NOK) if at least a portion of the trace data is above the upper curve and / or below the lower curve.

[0010] According to a second aspect, there is provided a method for a control system for one or more tools configured to install fasteners in a production process, the method comprising: obtaining a set of trace data for a plurality of test fastener setting operations performed on one type of joint by at least one of the one or more tools, the trace data including, for each fastener setting operation, a value indicative of setting force with respect to a value indicative of displacement or time, or a derivative thereof; deriving a maximum value or its derivative indicative of attachment force for each of a plurality of values ​​indicative of displacement or time from the set of trace data, and calculating a first polynomial based on these maximum values; deriving a minimum value or its derivative indicative of attachment force for each of a plurality of values ​​indicative of displacement or time from the set of trace data, and calculating a second polynomial based on these minimum values; setting an upper limit curve based on the first polynomial; setting a lower limit curve based on the second polynomial; further comprising In this method, in a production step subsequent to the production setting step, The method further includes determining a fastener setting operation performed by any one of the one or more tools as not passing (NOK) if at least a portion of the trace data exceeds the upper limit curve and / or falls below the lower limit curve.

[0011] The inventors have recognized that upper and lower limit curves for detecting NOK operations can be automatically created by calculating a polynomial based on the maximum and minimum values ​​of setting force (for each of multiple values ​​of displacement or time) or their derivatives for multiple test fastener installation operations. The area between the upper and lower limit curves may be referred to as the envelope of tolerance values. Thus, in this embodiment, an envelope defining the limits between OK / NOK values ​​can be automatically created. Because this envelope is based on a polynomial calculated based on the maximum and minimum values ​​of multiple actual test fastener installation operations for one type of joint, a balanced trade-off between leniency and strictness of the limit values ​​is ensured, thereby improving the accuracy of detecting NOK operations. By using a polynomial, the envelope curves (i.e., the upper and lower limit curves) do not track all irregularities in a single fastener installation operation. Instead, a smooth curve is provided for limiting the OK value from the NOK value.

[0012] Furthermore, by generating upper and lower limits in the form of a curve, it is possible to detect NOK operations, and evaluate not only the final maximum value, but also, in some cases, values ​​through one, several, or all of the different steps of the operation, which allows the detection of more types of NOK operations, such as stick-slip, where the final terminal torque is within an acceptable range but the torque oscillates during the torque build-up phase.

[0013] The polynomial can be calculated based on the values ​​indicative of the setting force versus displacement / time or based on the derivative (first or second order) of the values ​​indicative of the setting force versus displacement / time, both of which can be used as the basis for detecting OK / NOK fastener installation operations.

[0014] As used herein, the term "value indicative of the setting force" means the value of a parameter that somehow reflects / represents the force that the tool applies to the fastener. For example, if the tool is a fastening tool, such a parameter could be, for example, the torque sensed by a torque sensor of the tool, the motor current (representative of the torque), or the clamping force sensed by, for example, an ultrasonic sensor of the tool. As another example, if the tool is a riveting tool, such a parameter could be, for example, the motor current (which reflects the force applied by the tool to the rivet). Other parameters can also be envisaged.

[0015] Furthermore, in this specification, the term "value indicating displacement or time" means the value of a parameter that somehow reflects / represents the progress of the operation. In the case of a fastening tool, the parameter may be, for example, the angle sensed by an angle sensor. In the case of a riveting tool, the parameter may be the time from the start of the riveting operation. Other parameters may also be envisaged.

[0016] Furthermore, as used herein, the term "one type of joint" refers to a joint having the same characteristics. For example, test fastener installations can be performed on the same corresponding single joint in multiple identical assemblies. Alternatively, test fastener installations can be performed on multiple joints in one (or multiple identical) assemblies, as long as these joints have the same characteristics, such as stiffness (softness / hardness), friction, etc. For example, the joints can join the same pieces of material and contain the same type of fastener. Importantly, to generate an appropriate polynomial, it is desirable that the collected trace data of an OK fastener installation operation follow approximately the same path, at least for each step of the fastener installation operation.

[0017] For example, the upper and lower limit curves can be set to be equal to the first and second polynomials, respectively. Alternatively, a (small) marginal can be added to the polynomials. Preferably, the upper and lower limit curves can be set to follow the first and second polynomials, respectively.

[0018] According to one embodiment, the degree of the first and second polynomials is at least two, preferably at least three, most preferably at least four.

[0019] According to one embodiment, the degree of the first and second polynomials is at most six, preferably at most five.

[0020] A polynomial degree that is too low will result in poor adaptability, while a polynomial degree that is too high will result in a curve that is too oscillatory. We have found that a polynomial degree of around 4 to 5 is probably the best trade-off in this regard.

[0021] According to one embodiment, the first and second polynomials can be calculated using regression analysis, such as the least squares method, which provides an efficient method for approximating the polynomials that best fit the maximum and minimum values.

[0022] According to one embodiment, after acquiring the set of trace data of the test fastener installation operation and prior to the step of deriving the maximum and minimum values, the controller: - if the set of obtained trace data includes trace data that is deemed to represent a non-okay (NOK) test fastener installation operation, removing that trace data from the set; It can be further configured as follows.

[0023] This embodiment is advantageous in that the test trace data for NOK runs is removed / discarded before the maximum and minimum values ​​are derived, so the polynomial will only fit OK test runs, improving the accuracy of the resulting upper and lower limit curves.

[0024] Removal of trace data for NOK test fastener installation operations can be performed, for example, at the command of a user / operator (e.g., via input from a user interface) or can be performed automatically, for example, by using a machine learning model to identify NOK test fastener installation operations.

[0025] According to one embodiment, the control device performs the following steps in the production process: continuously monitoring whether at least a portion of the resulting trace data exceeds an upper curve and / or falls below a lower curve during a fastener setting operation performed by at least one of the one or more tools; It can be further configured as follows.

[0026] Thus, it is possible to detect that a fastener installation operation in progress is not going as desired before the entire operation is completed.

[0027] According to one embodiment, the control device comprises: - triggering an interruption (preferably immediately) of the fastener installation operation in response to the resulting trace data exceeding an upper curve and / or falling below a lower curve; It can be further configured as follows.

[0028] Thus, a fastener installation operation can be stopped as soon as the trace data falls outside the tolerance envelope, rather than waiting until the entire operation is completed before evaluation of the trace data. This embodiment is advantageous in that it prevents or at least reduces damage to the material into which the fastener is installed and to the fastener itself.

[0029] According to one embodiment, the tool may be a fastening tool or a riveting tool.

[0030] According to one embodiment, the control device comprises: - dividing the set of trace data into at least two sets representing at least two different steps of a fastener installation operation; - calculating a first and a second polynomial for each of said at least two steps; - setting upper and lower limit curves for each step based on the first and second polynomials calculated for each step, respectively; It can be further configured as follows.

[0031] That is, for each of the two sets of trace data, a maximum value indicative of installation force can be derived to calculate a first polynomial, and a minimum value indicative of installation force can be derived to calculate a second polynomial. Thus, different first polynomials can be provided for different steps, and different second polynomials can be provided for different sets. In other words, each of the multiple steps in a fastener installation operation will have its own upper and lower limit curves, which will better fit the test trace data for that step.

[0032] Examples of tightening steps include rundown (up to when the fastener head contacts the workpiece), snag (when the workpiece material strips are compressed), torque buildup (when compression is complete and the torque in the joint is built up), and braking (when the applied torque is discontinued).

[0033] According to one embodiment, there is provided a system comprising one or more tools configured to install fasteners in a production process and a controller as defined in accordance with the first aspect.

[0034] According to one embodiment there is provided a computer program comprising instructions which, when executed by a computer (such as a controller), cause the computer to carry out the method defined according to the second aspect.

[0035] According to one embodiment there is provided a computer readable storage medium comprising instructions which, when executed by a computer (such as a controller), cause the computer to perform the method defined according to the second aspect.

[0036] It should be noted that embodiments of the present invention relate to all possible combinations of the features recited in the claims. Furthermore, it should be understood that all of the various embodiments described for the control device can be combined with the method as defined according to the second aspect of the present invention.

[0037] These and other aspects will be explained in more detail in the following detailed description of illustrative and non-limiting embodiments, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0038] [Figure 1] 1 illustrates a system according to one embodiment. [Figure 2] 1 illustrates a graph of trace data according to one embodiment. [Figure 3]3 shows a graph of the trace data of FIG. 2 showing the trace data of the NOK operation. [Figure 4] 1 illustrates a graph of trace data according to one embodiment. [Figure 5] 1 illustrates a method according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0039] All figures are schematic, not necessarily to scale, and generally show only parts necessary to explain the embodiments, and other parts may be omitted. Like reference numerals refer to like elements throughout the specification.

[0040] A system 1 according to one embodiment will be described with reference to Figure 1. The system 1 comprises at least one tool 2 for installing a fastener 8 in a workpiece 7 in an industrial production process. The tool 2 may be, for example, a tightening tool (shown in Figure 1) for installing a screw fastener 8 or a riveting tool (not shown) for installing a rivet.

[0041] The system 1 may further include a controller 6 configured to control the tool 2. The controller 6 may be in communication with the tool 2, for example, by wire or wirelessly. The controller 6 may be a remote single unit (e.g., a computer as shown in FIG. 1 ), distributed across multiple units (e.g., cloud-based), and / or included in the tool 2. The controller 6 may comprise a memory for storing coded instructions and processing means for executing the coded instructions.

[0042] System 1 may optionally further include a display 5 for displaying information about the fastener installation operation being performed by tool 2. Display 5 may be a separate unit (as shown in FIG. 1) or may be incorporated into controller 6 and / or tool 2.

[0043] In industrial manufacturing, a pre-production setup process may be performed to set up the system 1 for the next production run. In such a pre-production setup process, the equipment to be used and the processing steps to be performed may be tested and configured for the particular assembly to be performed.

[0044] In this example, during such a pre-production setup process, upper and lower limit curves may be defined for the purpose of being able to detect that a fastener setting operation performed by tool 2 later in the production process is not acceptable (NOK). Such upper and lower limit curves may also be redefined / updated during subsequent production setup processes, for example, when a new lot of fasteners is used that has higher friction compared to previous lots. Examples of how these upper and lower limit curves may be set are described in more detail below.

[0045] 2 shows a graph 10 of a set of trace data 15 of test fastener installation operations performed by a tool on a joint during a production setup process (which may be a pre-production setup process or a subsequent production setup process). The trace data 15 for each operation may be displayed as a curve showing how a parameter T (e.g., torque) indicating the force applied to the fastener by the tool changes as the operation progresses. The operation progress is represented by a parameter α indicating either displacement (e.g., angle) or time.

[0046] Alternatively (or additionally), the trace data can be displayed as the derivative of the parameter T with respect to displacement or time α (not shown).

[0047] The controller may be configured to obtain this trace data 15 from the tool and, optionally, display it to the operator on a display (such as in the form of graph 10 shown in Figure 2).

[0048] If the acquired set of trace data 15 includes any test activity that is deemed NOK, the trace data for that activity can be removed, for example, by an operator or by a machine learning model.

[0049] The controller then determines from the set of trace data 15 the maximum value T of the attachment force (e.g., torque) for each of a plurality of displacement or time values ​​(e.g., angle) α. max and minimum value T min For simplicity, in Figure 2, we simply use some maximum values ​​T max and minimum value T min Although the maximum value T is shown for many more quantiles or time values ​​α, such as hundreds or thousands of quantiles or time values ​​α, depending on the sample rate of the trace data, max and minimum value T min It should be understood that it is possible to derive

[0050] Maximum value T max and minimum value T min The multiple displacement or time values ​​α for deriving T can represent, for example, a particular portion of the fastener installation operation or the entire fastener installation operation. Such a particular portion can correspond, for example, to a particular step in the fastener installation operation. In the example shown in FIG. 2, the maximum value T max and minimum value T min The multiple displacement or time values ​​α from which α is derived may represent torque build-up steps 13 of the tightening operation.

[0051] The control device further determines the maximum value T max Calculate the first polynomial based on the minimum T min For example, the polynomial can be calculated using a method based on regression analysis, such as the least squares method.

[0052] Next, the first polynomial is a basis for setting the upper limit curve 11, and the second polynomial is a basis for setting the lower limit curve 12. For example, the upper and lower limit curves 11, 12 may be equal to the first and second polynomials, respectively (as shown in FIG. 2). Alternatively, the upper and lower limit curves 11, 12 may be set slightly offset from the first and second polynomials. As can be seen from FIG. 2, the upper and lower limit curves 11, 12 are set to a value that is equal to the maximum value T max and minimum value T min Preferably, the degree of the first and second polynomials is between 2 and 6, for example 4 or 5.

[0053] Optionally, the upper and lower curves 11, 12 may be editable by the user before being finally set.

[0054] In subsequent production steps, these limit curves 11, 12 can be used to detect NOK fastener installation operations, as will be explained below with reference to FIG.

[0055] During a production process, the control device is configured to acquire, preferably continuously, trace data 16 of operations performed by the tool. If this trace data 16 is detected to fall outside the envelope defined by the upper and lower limit curves 11, 12, the operation is determined to be a non-operational-key operation. The trace data 16 can be continuously monitored against the limit curves 11, 12 during the operation, and the operation can be interrupted as soon as the trace data 16 falls outside the envelope. Alternatively, the trace data 16 can be compared with the limit curves 11, 12 after all operations have been completed.

[0056] In the example shown in Figure 3, trace data 16 of a tightening operation that includes stick-slip is shown. As can be seen, trace data 16 oscillates 17 outside the envelope defined by limit curves 11 and 12. Therefore, the operation will be classified by the control device as an NOK operation.

[0057] For example, the control device may be further configured to display the results of the OK / NOK classification of the work on a display and / or record / store them in a production control system.

[0058] According to one embodiment, the control device can be configured to divide the trace data of the operation into a number of sets, each corresponding to a predefined step of the operation. In the example shown in Figure 4, the tightening operation is divided into the steps of run down 21, snug 22, torque buildup 23, and braking 24. Here, for a number of displacement or time values ​​α defined for each step 21, 22, 23, 24, the maximum value T max and minimum value T min The limits between different steps can be defined not as numerical values ​​of displacement or time, but as when certain conditions are met. For example, the snag step 21 can be defined to end when the torque starts to rise. These maximum values ​​T max and minimum value T min Based on this, one first polynomial and one second polynomial are calculated for each one of steps 21, 22, 23, and 24. Then, upper limit curves 211, 221, 231, and 241 and lower limit curves 212, 222, 232, and 242 for each step can be set appropriately.

[0059] The trace data curves may be aligned for each step 21, 22, 23, 24. However, this is merely a matter of representation, and when calculating the polynomial, the associated displacement or time values ​​for the particular step of interest are used to derive the maximum and minimum values.

[0060] A method 100 according to one embodiment will now be described with reference to Figure 5. The method 100 may be performed by a controller such as that described with reference to Figure 1.

[0061] The method 100 includes a production setup step 101: a) obtaining a set of trace data for a plurality of test fastener setting operations performed on one type of joint by at least one of one or more tools, the trace data including, for each fastener setting operation, a value indicative of setting force versus a value indicative of displacement or time, or a derivative thereof; b) optionally, if the acquired set of trace data includes trace data that is deemed to represent a non-okay (NOK) test fastener installation operation, removing the trace data; c) deriving a maximum value or a derivative thereof indicative of attachment force for each of a plurality of values ​​indicative of displacement or time from the set of trace data, and calculating a first polynomial based on these maximum values; d) deriving a minimum value indicative of attachment force or its derivative for each of a plurality of values ​​indicative of displacement or time from the set of trace data, and calculating a second polynomial based on these minimum values; e) setting an upper limit curve based on the first polynomial; f) setting a lower limit curve based on the second polynomial; Includes.

[0062] The method 100 further includes, in a production step 102 following the production setup step 101, g) determining a fastener setting operation performed by any one of the one or more tools as not passing (NOK) if at least a portion of the trace data is above an upper limit curve and / or below a lower limit curve; Optionally, the fastener installation operation can be determined to be otherwise OK.

[0063] Optionally, method 100 further comprises: h) triggering an interruption of the fastener installation operation in response to the resulting trace data exceeding an upper curve and / or falling below a lower curve; and / or i) notifying an operator of the determination result of step g) and / or storing the result in a production control system; may include:

[0064] It should be understood that all of the described embodiments of the control device can be combined with the method embodiments.

[0065] Those skilled in the art will understand that the invention is not limited to the embodiments described above, but rather many modifications and variations are possible within the scope of the claims.

[0066] In addition, by studying the drawings, the disclosure and the claims, those skilled in the art will understand and effect variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A control device (6) for one or more tools (2) configured to install fasteners (8) in a production process, comprising: The control device, in the production setting step, - obtaining a set of trace data (15) relating to a plurality of test fastener setting operations performed on one type of joint by at least one of said one or more tools, said trace data including, for each fastener setting operation, a value indicative of setting force or a derivative thereof with respect to a value indicative of displacement or time; From the set of trace data, for each of a plurality of values ​​(α) indicating displacement or time, a maximum value (T max ) or its derivative, and calculating a first polynomial based on the maximum value; From the set of trace data, for each of a plurality of values ​​(α) indicating displacement or time, a minimum value (T min ) or its derivative, and calculating a second polynomial based on the minimum value; - setting an upper limit curve (11) based on said first polynomial, - setting a lower limit curve (12) based on said second polynomial; It is structured as follows: The control device, in a production process subsequent to the production setting process, determining that the fastener setting operation performed by any one of said one or more tools is unacceptable (NOK) if at least a portion of the trace data (16) is above an upper curve limit and / or below a lower curve limit; The control device is further configured as follows.

2. The control device of claim 1 , wherein the degree of the first and second polynomials is at least two.

3. 3. The control device according to claim 1, wherein the degree of the first and second polynomials is up to six.

4. The control device according to claim 1 , wherein the first and second polynomials are calculated using regression analysis such as the least squares method.

5. after obtaining the set of trace data for the test fastener installation operation and prior to deriving the maximum and minimum values; - if the acquired set of trace data includes trace data that is deemed to represent a failing (NOK) test fastener installation operation, removing the trace data; The control device according to claim 1 , further configured to:

6. In the production process, - continuously monitoring whether at least a portion of the resulting trace data exceeds an upper curve and / or falls below a lower curve during a fastener setting operation performed by at least one of said one or more tools; The control device of claim 1 , further configured to:

7. - triggering an interruption of the fastener installation operation in response to the resulting trace data exceeding the upper curve limit and / or falling below the lower curve limit; 7. The control device of claim 6, further configured to:

8. The control device according to claim 1 , wherein the tool is a fastening tool or a riveting tool.

9. - dividing said set of trace data into at least two sets representing at least two different steps (21, 22, 23, 24) of a fastener installation operation; - calculating a first and a second polynomial for each of said at least two steps, - setting upper and lower limit curves (211, 221, 231, 241) and (212, 222, 232, 242) for each step based on the first and second polynomials calculated for each step, respectively; The control device of claim 1 , further configured to:

10. - one or more tools (2) configured to install fasteners (8) in a production process; - a control device (6) according to any one of claims 1 to 9, A system (1) comprising:

11. 1. A method (100) for a control system for one or more tools configured to install fasteners in a production process, comprising: (a) obtaining a set of trace data for a plurality of test fastener setting operations performed on one type of joint by at least one of the one or more tools, the trace data including, for each fastener setting operation, a value indicative of setting force with respect to a value indicative of displacement or time, or a derivative thereof; (c) deriving a maximum value or its derivative indicative of attachment force for each of a plurality of values ​​indicative of displacement or time from the set of trace data, and calculating a first polynomial based on the maximum value; (d) deriving from the set of trace data a minimum value indicative of attachment force or its derivative for each of a plurality of values ​​indicative of displacement or time, and calculating a second polynomial based on the minimum value; (e) setting an upper limit curve based on the first polynomial; (f) setting a lower limit curve based on the second polynomial; further comprising In the production process (102) following the production setting process, (g) rejecting a fastener setting operation performed by any one of the one or more tools if at least a portion of the trace data is above the upper limit curve and / or below the lower limit curve; The method further comprises:

12. A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method of claim 11.

13. A computer-readable storage medium containing instructions that, when executed by a computer, cause the computer to perform the method of claim 11.

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