Impulse screw tightening process including stiffness measurement

Abstract

The present invention relates to a screwing system comprising a device for pulsed screwing of a screw element, said screwing device comprising at least: - a motor; - an output shaft capable of being driven in rotation by said motor; - angle measuring means capable of measuring at least one quantity representative of the angle of rotation of said output shaft; - torque measuring means capable of measuring at least one quantity representative of the tightening torque delivered by said output shaft; said system further comprising: - a controller of said motor capable of controlling said motor so that said output shaft delivers a plurality of successive screwing pulses capable of being transmitted to said screw element;- a processing unit capable of generating generated torque / angle pairs, each generated pair comprising a torque value and an angle value recorded simultaneously by said torque measurement means and by said angle measurement means during at least a portion of said pulses. According to the invention, said processing unit is capable of determining, from at least some of said generated torque / angle pairs, a function representative of a torque / angle characteristic of said screw-in element.

Description

Title of the invention: Impulse screw-driving method including stiffness measurement 1. Scope of the invention

[0001] The field of the invention is that of impulse screwing techniques. 2. Prior art

[0002] It is often necessary in various fields to tighten screw-on elements to create assemblies.

[0003] For this purpose, it is common to use continuous tightening screw devices during the implementation of which a tightening torque, constant or variable, is continuously delivered to the element to be screwed.

[0004] Screwing devices of this type have the disadvantage of transmitting, during a screwing operation, a high reaction torque into the hand of the operator so that they cannot be used to carry out screwing operations requiring tightening assemblies with too high a tightening torque.

[0005] To enable screwdriving operations to be carried out at a higher tightening torque without transmitting excessive reaction torque to the operator, impact screwdriving devices have been developed. These devices, also called impact wrenches, typically comprise a motor and an output shaft linked by an impact mechanism including at least a hammer and an anvil.

[0006] More recently, impulse tightening devices have been developed in parallel. These tightening devices have a structure similar to that of continuous tightening devices and therefore, unlike impact tightening devices, do not include an impact mechanism. Using a different approach, impulse tightening devices exploit the backlash in the transmission between the motor and the output shaft to generate torque pulses that are transmitted to the element to be tightened. These torque pulses are generated by supplying the motor with current pulses. Impact tightening devices have the advantage of being able to achieve high tightening torques while significantly limiting the reaction torque transmitted to the operator.

[0007] In industrial screwdriving applications, it is important that the screwdriving device stops as soon as the target tightening torque is reached, in order to comply with design specifications. To achieve this, it is necessary to measure the tightening torque delivered by the screwdriving device.

[0008] On continuous tightening screw devices, the tightening torque measurement is conventionally carried out via a torque sensor consisting of a deforming element Equipped with strain gauges, positioned between the gear transmission interposed between the motor and the output shaft, and the housing of the screw-driving device, this provides a reading of the tightening torque present in the output shaft and therefore of the torque transmitted to the workpiece while the screw-driving operation is in progress. Once it is detected that the target tightening torque has been reached, the screw-driving device's control means stop the motor to terminate the ongoing screw-driving operation.

[0009] On impulse screwdriving devices, the tightening torque is measured in the same way. However, due to the discontinuous transmission of tightening torque, i.e. by impulses, the tightening torque is only transmitted to the sensor at the moment of impact in the transmission generating the torque impulse.

[0010] Pulse screwdriving devices are equipped with calculation means designed to detect the tightening torque during each pulse, in order to know whether the tool should stop at the end of the current pulse or perform a new pulse.

[0011] The result of the tightening torque, as well as the screwing curve (torque / angle), are generally transmitted to curve processing / storage means.

[0012] These processing / storage means can thus display reporting information, issue alerts, launch actions based on the result of torque, etc... or store these curves for subsequent processing, manual or automatic.

[0013] The transient nature of torque pulses leads to dynamic phenomena, sometimes very significant, in the signal measured by the torque sensor. These phenomena can be more or less significant depending, in particular, on:

[0014] - of the target torque level,

[0015] - characteristics (stiffness, inertia, etc.) of the element to be screwed,

[0016] - characteristics (stiffness, inertia, etc.) of the accessories used at the end of the output shaft (sockets, extensions, etc...), etc...

[0017] It is sometimes difficult for the computing means to detect the torque installed in the screw from the signal transmitted by the sensor.

[0018] This results in less precision of the screwing device since it will stop too early (not enough pulses) or too late (too many pulses) leading to the tightening torque reached at the end of the screwing operation being either lower or higher than the target tightening torque.

[0019] The screwing curves transmitted to the processing means are also not representative of the actual screwing curve of the assembly, which can lead to erroneous processing of information.

[0020] There is therefore a need to improve the measurement of the tightening torque delivered by impulse screw-driving devices. 3. Objectives of the invention

[0021] The invention aims in particular to provide an effective solution to at least some of these different problems.

[0022] In particular, according to at least one embodiment, an objective of the invention is to provide a technique which makes it possible to make the measurement of the tightening torque delivered by an impulse tightening device more reliable.

[0023] In particular, the invention aims, according to at least one embodiment, to provide such a technique which makes it possible to obtain a tightening torque / screwing angle characteristic which is representative of that of the screwed assembly.

[0024] Another objective of the invention is, according to at least one embodiment, to provide such a technique which makes it possible to provide a stiffness function representative of the tightening torque installed in the element to be screwed, and this despite the dynamic phenomena which can be perceived by the torque sensor.

[0025] Another objective of the invention is, according to at least one embodiment, to provide such a technique which makes it possible to use a stiffness function representative of the tightening torque installed in the screwing element, i.e. the relation Torque = f(angle) in order to estimate the angle for which the target tightening torque will be reached and to stop the tool when this angle is reached.

[0026] Another objective of the invention is, according to at least one embodiment, to provide such a technique which allows to archive noise-free tightening curves in order to allow human or computer processing (for example: machine learning) on ​​curves representative of the bolted assembly.

[0027] Another objective of the invention is, according to at least one embodiment, to provide such a technique which makes it possible to characterize an assembly (stiffness, etc...) for example to ensure control of an assembly process.

[0028] Another objective of the invention is, according to at least one embodiment, to provide such a technique which is simple and / or reliable and / or robust and / or economical. 4. Presentation of the invention

[0029] For this purpose, the invention proposes a system comprising a device for screwing with impulses of an element to be screwed, said screwing device comprising at least:

[0030] - a motor;

[0031] - an output shaft capable of being driven in rotation by said motor;

[0032] - angle measurement means capable of measuring at least one quantity representative of the angle of rotation of said output shaft;

[0033] - torque measurement means capable of measuring at least one quantity representative of the tightening torque delivered by said output shaft;

[0034] said system further comprising:

[0035] - a controller of said motor capable of driving said motor so that said shaft of output delivers a plurality of successive screwing pulses that can be transmitted to the said element to be screwed;

[0036] - a processing unit capable of generating generated torque / angle pairs, each generated couplet comprising a torque value and an angle value recorded simultaneously by said torque measurement means and by said angle measurement means during at least a part of said pulses.

[0037] According to the invention, said processing unit is capable of determining, from at least some of said generated torque / angle pairs, a function representative of a torque / angle characteristic of said screw element.

[0038] The invention thus makes it possible to obtain a torque / angle characteristic representative of the screwed assembly which can then be used to regulate a screwing operation by abstracting from the dynamic phenomena which, according to the prior art, impair the precision.

[0039] It should be noted that the stiffness of an assembly is not necessarily purely linear. Thus, the function is not necessarily representative of the stiffness over the entire tightening process but only over a portion, particularly at least towards the end of tightening. Indeed, especially when this function is used to stop the tool, it is essential that the function be representative of the stiffness at the end of tightening (that is, when the torque reaches values ​​close to the target torque).

[0040] According to one possible feature, said processing unit is capable of determining, for each pulse of said at least a part of the pulses, at least one characteristic torque / angle couplet of said pulse, each characteristic couplet being determined from said generated couplets (i.e. selected from or calculated from), said function being determined from said characteristic couplets determined for each pulse of said at least a part of the pulses.

[0041] According to one possible feature, said processing unit is capable of generating said function by determining a regression function of at least a part of said characteristic couplets determined at each pulse of said at least a part of the pulses.

[0042] According to one possible feature, said processing unit is capable, at the end of each pulse of said at least a part of said pulses, of rejecting or weighting said at least one characteristic couplet of the pulse considered, for the determination of said regression function.

[0043] According to one possible feature, said processing unit is capable of rejecting said at least one characteristic couplet of said impulse when the distance of said at least one characteristic couplet from the determined regression function from the characteristic couplets of the pulses preceding said pulse in question, exceeds a predetermined threshold distance.

[0044] According to one possible characteristic, said processing unit is capable of determining, during at least one of said pulses, at least one useful angle value representative of a state of progress of the screwing of said element to be screwed at the end of said pulse.

[0045] According to one possible characteristic, said processing unit is capable of determining a theoretical tightening torque value reached at the end of said impulse from said at least one useful angle value and said function.

[0046] According to one possible characteristic, said controller is capable of:

[0047] - to detect the attainment of a predetermined screwing stop criterion;

[0048] - to stop said motor when said screw stopping criterion is reached;

[0049] said processing unit being capable of comparing said theoretical torque value of tightening of the considered impulse with a predetermined target torque value, said predetermined tightening stop criterion being a function of the result of this comparison

[0050] According to one possible feature, the achievement of said screw-stopping criterion consists of exceeding said predetermined target torque value by said theoretical torque value.

[0051] According to one possible feature, said processing unit is capable of comparing said determined function to a predefined theoretical function characteristic of said screwing element, said screwing system including alerting means, said alerting means being capable of issuing an alert when said determined function is far from the predefined theoretical function beyond a predetermined distance criterion.

[0052] The invention also covers a method for pulse-driven screwing of a screw element by means of a pulse-driven screwing system according to any one of claims 1 to 10, said method comprising at least:

[0053] - a step of controlling said motor by said controller so that said shaft of output delivers a plurality of successive screwing pulses to said element to be screwed;

[0054] - a measurement step using said angle measuring means of a quantity representative of the angle of rotation of said output shaft;

[0055] - a measurement step using said torque measurement means of a quantity representative of the tightening torque delivered by said output shaft;

[0056] - a step of generating by said torque / angle couplet processing unit generated, each generated couplet comprising a torque value and an angle value recorded simultaneously by said torque measurement means and by said angle measurement means during at least a part of said pulses.

[0057] According to the invention, such a method includes a step of determining by said processing unit, from at least some of said generated torque / angle pairs, a function representative of a torque / angle characteristic of said screw element.

[0058] According to one possible feature, a method according to the invention comprises a step of determining by said processing unit, for each pulse of said at least a part of said pulses, at least one characteristic torque / angle couplet of said pulse, each characteristic couplet being determined from said generated couplets, said function being determined by said processing unit during said determination step from said characteristic couplets determined for each pulse of said at least a part of said pulses.

[0059] According to one possible feature, said step of determining said function comprises a step of generating by said processing unit a regression function of at least a part of said characteristic couplets determined at each pulse of said at least a part of said pulses

[0060] According to one possible feature, a method according to the invention comprises, at the end of each pulse of said at least a part of said pulses, a step of rejection or weighting by said processing unit of said at least one characteristic couplet of the pulse considered, with a view to determining said regression function.

[0061] According to one possible feature, said processing unit is capable of rejecting said at least one characteristic couplet of said pulse when the distance of said at least one characteristic couplet from the regression function determined from the characteristic couplets of the pulses preceding said pulse in question exceeds a predetermined threshold distance

[0062] According to one possible feature, a method according to the invention includes, during at least a part of said pulses, a step of determining by said processing unit at least one useful angle value representative of a state of progress of the screwing of said element to be screwed at the end of said pulse.

[0063] According to one possible feature, a method according to the invention includes a step of determining by said processing unit a theoretical tightening torque value reached at the end of said impulse from said at least one useful angle value and said function.

[0064] According to one possible feature, a method according to the invention comprises:

[0065] - a step of detection by said controller of the attainment of a predetermined criterion screw stop;

[0066] - a step of stopping said motor by said controller when said stopping criterion of screwing is achieved;

[0067] said method further comprising a step of comparison by said processing unit, of said theoretical tightening torque value of the considered impulse with a predetermined target torque value, said predetermined screwing stop criterion being a function of the result of this comparison.

[0068] According to one possible feature, said achievement of said predetermined screwing stop criterion corresponding to an exceeding of said predetermined target torque value by said theoretical torque value.

[0069] According to one possible feature, a method according to the invention includes a step of comparing, by said processing unit, said determined function to a predefined theoretical function characteristic of said screw element, and a step of issuing an alert by said alerting means when said determined function is far from the predefined theoretical function beyond a predetermined distance criterion.

[0070] The invention also covers a computer program product comprising program code instructions for implementing a process according to any of the above variants when executed by a processor.

[0071] The invention also covers a computer-readable recording medium comprising program code instructions which, when executed by a processor, cause the processor to implement a process according to any of the above variants. 5. Description of the figures

[0072] Other features and advantages of the invention will become apparent from the following description of particular embodiments, given by way of simple illustrative and non-limiting example, and the accompanying drawings, among which:

[0073] [Fig-1] [Fig.1] illustrates a diagram of a pulse screwdriving system according to the invention;

[0074] [Fig.2] [Fig.2] illustrates the variation as a function of temperature of the tightening torque and of the screwing angle during a screwing operation;

[0075] [Fig.3] [Fig.3] illustrates the variation in tightening torque during an impulse screwing;

[0076] [Fig.4] [Fig.4] illustrates the variation in screw angle during a pulse of screwing;

[0077] [Fig. 5] [Fig. 5] illustrates a cloud of torque / screwing angle bridges screwing generated;

[0078] [Fig.6] [Fig.7] [Fig.6] illustrates one way of obtaining a characteristic couplet and the [Fig.7] illustrates the characteristic couplets of the impulses of a screwing;

[0079] [Fig.8] [Fig.8] illustrates a linear regression of characteristic couplets;

[0080] [Fig.9] [Fig.9] illustrates a flowchart of an example of a process according to the invention.

[0081] 6. Description of particular embodiments 6.1. Screwing system

[0082] An example of a pulse screwing system 1 according to the invention is presented in relation to [Fig.1].

[0083] Such a system comprises:

[0084] - a pulse screwing device 10;

[0085] - a controller 11;

[0086] - a processing unit 12.

[0087] These elements will now be described. 6.1.1. Screwing device

[0088] A screwing system according to the invention comprises a screwing device 10.

[0089] In a conventional manner, the impulse screwing device includes a housing 100 containing an electric motor M comprising a rotor.

[0090] At one end of the housing extends a rotating output shaft 101 capable of being driven in rotation by the rotor.

[0091] For this purpose, the housing accommodates a transmission T having an input connected to the rotor and an output connected to the output shaft.

[0092] This transmission comprises a plurality of gears, for example one or more epicyclic gear trains.

[0093] This transmission includes mechanical operating clearances between the gears so as to allow the gears to rotate relative to each other and thus drive the output shaft in rotation under the effect of a rotation of the rotor.

[0094] The play in the transmission is exploited to generate, during a screwing operation, screwing pulses during each of which an impact occurs in the transmission.

[0095] The screwing device includes a torque sensor 102 capable of measuring at least one quantity representative of the tightening torque delivered by the output shaft.

[0096] This torque sensor may, for example, comprise a deforming element that prevents the rotation of the ring gear of an epicyclic gear train of the transmission relative to the housing, and that carries strain gauges. The deformation of this deforming element, when the tightening device delivers a tightening torque applied to the output shaft, is proportional to this tightening torque.

[0097] In variants, the torque sensor may be:

[0098] - a dynamic sensor, that is to say a sensor located on the output shaft of the tool and comprising means for transmitting at least one quantity representative of the tightening torque to the tool controller;

[0099] - a deceleration sensor for measuring a deceleration representative of the torque applied to the output shaft;

[0100] - any other torque sensor known to a person skilled in the art.

[0101] The screwing device includes an angle sensor 103 capable of measuring at least one quantity representative of the angle of rotation of the output shaft relative to the housing of the screwing device.

[0102] This angle sensor may, for example, include a resolver located on the rotor shaft or any other angle sensor known to a person skilled in the art.

[0103] A screw-driving device according to the invention may also include a sensor for measuring the rotation of the housing relative to the environment. By way of example, this sensor may include an inertial measurement unit (IMU). In a manner known to those skilled in the art, the signal delivered by this sensor may allow the angle measured by the angle sensor to be corrected to account for any rotation of the tool relative to its surroundings.

[0104] The screwing device is conventionally connected to a controller which will now be described. 6.1.2. Controller

[0105] A screwing system according to the invention includes a controller 11.

[0106] Such a controller is known in itself to a person skilled in the art and is not described in further detail here. It comprises all the elements and is programmed to enable the execution of a process according to the invention, and in particular impulse screwing operations.

[0107] The controller can be housed in the casing of the screwing device or be located outside of this casing.

[0108] Whether housed in the casing or not, the controller can be connected to the screwing device by wired or wireless means.

[0109] The screwing system controller is capable of driving the screwing device motor so that the output shaft delivers a plurality of successive screwing pulses that can be transmitted by the output shaft to a screwing element.

[0110] Thus, with each pulse, a torque pulse is transmitted to the output shaft, these torque pulses increasing successively until the screw element is tightened to the desired target torque. This principle is known per se and is, for example, described in detail in patent documents bearing numbers FR-A1-2 974 320, FR-A1-3 003 495, FR-A1-3 015 332. 6.1.3. Processing Unit

[0111] A screwing system according to the invention comprises a processing unit 12.

[0112] This processing unit may or may not be housed in the casing.

[0113] Whether or not it is housed in the casing, the processing unit may or may not be integrated into the controller.

[0114] This processing unit is capable of generating generated torque / angle couplets, each generated couplet comprising a torque value and an angle value recorded simultaneously by the torque sensor and by the angle sensor during at least a portion of the pulses.

[0115] Furthermore, according to the principle of the invention, this processing unit is capable of determining, from at least some of the generated torque / angle pairs, a function representative of a torque / angle characteristic of a screw-on element.

[0116] The processing unit is not described in more detail here and is suitable for carrying out the steps that it helps to implement of a process according to the invention, as will become clearer later. 6.2. Screwing method

[0117] We now describe, in relation to [Fig.9], a method of impulse screwing of a screw element by means of an impulse screwing system according to the invention.

[0118] Such a process is implemented during a screwing operation of a screwable element.

[0119] During such a process, a step in which the motor is driven by the controller is implemented so that the output shaft delivers a plurality of successive tightening torque pulses to the element to be screwed. For this purpose, the controller supplies the motor with successive electrical pulses. 6.2.1. Angle measurement and tightening torque

[0120] During the implementation of such a process, the following are also implemented:

[0121] - a measurement step using the angle sensor of a quantity representative of the angle output shaft rotation: a(t);

[0122] - a measurement step by the torque sensor of a quantity representative of the tightening torque delivered by the output shaft: C(t).

[0123] These steps are preferably implemented in real time throughout the implementation of a screwing operation.

[0124] Thus, during the implementation of a process according to the invention, signals representative of the variation over time of the screwing angle and tightening torque are obtained by means of the torque sensor and the angle sensor, such as those illustrated by the curves in [Fig.2].

[0125] These signals can be analog signals (continuous signals) or digital signals (discrete sampled signals).

[0126] Figures 3 and 4 respectively illustrate an example of variation as a function of time of the torque C(t) and of the screw angle a(t) for an impulse.

[0127] The results of angle and torque measurements can be filtered, for example:

[0128] - by using a low-pass filter (digital or analog, for example an anti- (folding)

[0129] - by applying a sliding range regression to the sampled signal (mean, linear, polynomial, etc.), for example a weighted regression, for example using the Savisky-Golay algorithm 6.2.2. Generated torque / angle pairs

[0130] The processing unit takes into consideration the signals delivered by these torque and angle sensors to generate, during a generation step, generated torque / angle couplets (Cp «,).

[0131] Each generated couplet (Qa) comprises a torque value (Ca) and an angle value (θi) recorded simultaneously at time h by the torque sensor and the angle sensor during at least part of the pulses. The time increments are determined by the processing unit, for example, by sampling the angle and torque signals at the same sampling frequency in the case of analog signals, or by reusing the lowest common sampling frequency of the angle and torque signals in the case where these signals are already digital signals. In the case where the torque and angle signals have different sampling frequencies, the processing unit can take, for the signal with the lowest sampling frequency, the value of the last known sample.The processing unit can also interpolate the values ​​of two samples for the signal with the lowest sampling frequency, so as to generate intermediate values ​​corresponding to the higher sampling frequency.

[0132] These couplets thus make it possible to illustrate the variation of the tightening torque as a function of the tightening angle.

[0133] A numerical processing method can be applied by the processing unit to the point cloud corresponding to the generated couplets (Q cq), so as to facilitate its use. Any numerical processing method known to a person skilled in the art can be considered.

[0134] 6.2.3. Function representing a torque / angle characteristic of the element to screw i. General principle

[0135] In addition, the processing unit performs a determination step, based on at least some of the torque / angle pairs (Q "J generated in the previous step, of a functional such as ç— f O representative of a torque / angle characteristic of the element to be screwed.

[0136] In general, this function ft is representative of a torque / angle characteristic of the element to be screwed, in particular representative of the stiffness of the element to be screwed or of the assembly.

[0137] It may, for example, be taken into consideration:

[0138] - by an operator, in particular the user of the screwing device, to provide him an image of the torque increase of the assembly as a function of the angle;

[0139] - to establish the stiffness curve of the assembly.

[0140] The stiffness curve of the assembly is likely to be taken into account for:

[0141] - the control of the tool;

[0142] - reporting (alerting on the stiffness of a joint which is not that expected);

[0143] - curve processing (machine learning, etc...).

[0144] The generation of the generated torque / angle pairs ( , ), as well as the determination of the function ft, can be carried out in real time, but also a posteriori from the recording of the angle measurements a(t) and torque C(t) (for example during subsequent processing in an external computer system).

[0145] ii. Determination of the representative function of a torque / angle characteristic of the screw element

[0146] The generation by the processing unit of the function ft representing a torque / angle characteristic of the screw element is described below. ii.l. Generated verses

[0147] Whether the function / t is determined in real time or a posteriori, it can be determined from one or more generated pairs for all the pulses or for certain pulses only. In other words, it is possible to consider only the pulses on one or more portions of a screwing operation and not necessarily on the entire screwing operation.

[0148] Reducing the number of pulses considered, on the one hand, and the number of generated torques considered per pulse, on the other hand, reduces computation time. This also allows focusing on certain pulses (for example, at the beginning of tightening to reduce dynamic phenomena, or at the end of tightening to obtain a characteristic closer to the final tightening stiffness).

[0149] For example, the impulses can only be taken into account once a certain low threshold value of tightening torque is reached, and / or up to a certain high threshold value of torque. These torque threshold values ​​can, for example, be determined as a percentage of the target torque (i.e., the final tightening torque to which the assembly is to be tightened). As an example, the processing unit may only generate the couplets ( Cj, at ) generated only for impulses during which the torque exceeds 30% of the target torque and during which the torque does not exceed 80% of the target torque.

[0150] The character function f is then determined by the processing unit only from these verses generated during these pulses.

[0151] The couplets (Q) generated by the processing unit can be represented in the form of a point cloud as illustrated in Figure 5. This figure illustrates in the form of a point cloud the couplets generated (C^ az) for a pulse. ii.2. Characteristic couplets

[0152] Preferably, the method includes a step of determining by the processing unit, for each pulse of the set of pulses or of only a part of the pulses, at least one characteristic couplet / angle (caract) of the pulse considered.

[0153] The use of characteristic couplets makes it possible to improve and / or simplify the calculation of the function.

[0154] In this embodiment, the generated torques are generated throughout a tightening cycle (i.e., until the target tightening torque is reached) and not only during pulses or certain pulses. In contrast, the characteristic torques are determined only for the pulses of which they are characteristic.

[0155] Thus, to determine the characteristic torques, it is necessary to detect the presence of an impulse. The ability to detect an impulse is known to those skilled in the art. For example, the impulse can be considered to begin when the measured torque exceeds a certain threshold value and to end when it falls below this threshold value. Alternatively, the impulse can be considered to begin when the angle exceeds the angle value reached in the previous impulse (or after the initial tightening for the first impulse) and to end when the angle falls below this value. Any other detection method known to those skilled in the art can be considered (speed changing to 0, etc.).

[0156] In variants, the generated verses may only be generated during all or part of the pulses, which will require detecting the pulses for example as indicated above.

[0157] More generally, for any processing related to a pulse, it will be necessary to detect this pulse, for example as indicated above.

[0158] Each characteristic couplet (Ccaraco aearact) is determined by the processing unit from the generated couplets (Q.

[0159] A characteristic torque / angle couplet (Ccaract, acuract) of a pulse can be one of the couplets generated by the processing unit from the measured torque and angle values. Alternatively, it can also be a new couplet, for example having a certain torque value calculated from the torque values ​​of the generated couplets, and an angle value calculated from the angle values ​​of the generated couplets, or a mixture of measured and calculated values...

[0160] There are thus several ways of determining, for example by calculation or by selection, a characteristic couplet (C^ad, acaract) of an impulse.

[0161] For example, one can, for the determination of the characteristic couplet (Ccaract, acaract) of a pulse, select as characteristic couplet (Ccaract, acaract) of this pulse, the couplet (Cp among the generated couplets of the pulse whose couplet value C, is maximum.

[0162] For example, one can, for the determination of the characteristic couplet (Cearact, acaroct) of a pulse, select as the characteristic couplet (Ccarady acaract) of that pulse, the couplet (Q af) among the generated couples of that pulse whose torque value C{ is a predefined local extremum of torque. For example, one can select the generated couplet (C;, whose torque value Ci is the last local maximum of torque of the pulse.

[0163] For example, for the determination of the characteristic couplet (Ccm.act, acaract) of a pulse, one can select as the characteristic couplet (CCaract, acaract) of this pulse, the couplet (Ç, a / ) among the generated couples of this pulse whose angle value ai is maximum.

[0164] According to another example, the torque value Ccaract and / or the angle value acaract of the characteristic torque (Ccaract, acaract) of a pulse can be calculated from the generated torques (Cp) for that pulse. For example, the torque value Ccaract of the characteristic torque (Ccaracp acaract) can be calculated as the average of the torque values ​​C of the generated torques (Q a / ) for that pulse that are greater than a threshold torque value. This principle is illustrated in Figure 6. In Figure 6, the angle value (lcaract) of the characteristic torque (Ccaract, acaroct) is always the maximum angle value of the pulse.

[0165] The processing unit thus obtains a characteristic couplet (Ccaract, acaract) for at least some of the pulses as shown in [Fig.7].

[0166] ii.3. Generation of the representative function of a torque / angle characteristic of the screw-on element

[0167] The function f canKt such that -f O , representative function of a The characteristic torque / angle of the screwing element is determined by the unit of processing during the determination step from the characteristic couplets {Ccara£t, acaract) determined previously.

[0168] This function f represents a torque / angle characteristic of the element at Cui llLl The screwing can perhaps be determined by the processing unit in several ways.

[0169] For example, to generate this function, the processing unit generates a regression function of at least a part of the characteristic couplets (Ccaraco acarœt) determined beforehand.

[0170] This regression function may be of linear type, as illustrated in [Fig.9].

[0171] Alternatively, this regression function may be polynomial.

[0172] Before determining the function f, the characteristic torques iCcariât- (icaract) can in turn be smoothed. That is to say, the torque values ​​C£aract of the characteristic torques can be corrected so as to reduce the variations in the torque of the characteristic torques from one impulse to another.

[0173] To this end, the processing unit can perform:

[0174] - a regression (mean, linear, polynomial, etc.) on the values ​​of the pair Character of the characteristic verses on a slippery beach;

[0175] - a weighted regression, for example using the Savisky-Golay algorithm, on the torque values ​​Ccaract of the characteristic torques

[0176] The curve, i.e. the function f, such that „ f [3 where C is the screwing torque cm üci — / i ex । J caractx / and a is the screwing angle, thus obtained by the processing unit is, as previously indicated, representative of a torque / angle characteristic of the element to be screwed, in particular representative of the stiffness of the element to be screwed.

[0177] ii.4. Rejection or weighting of characteristic couplets

[0178] Optionally, the processing unit may implement, at the end of each pulse n for which it defines a characteristic couplet (^amict' acaract\f), a step of rejecting or weighting the characteristic couplet of the pulse in question, with a view to determining the regression function f J caradn

[0179] Thus, the processing unit may be able to reject the characteristic couplet(s) (caraco acaruct)„ of a pulse n when the distance of the characteristic couplet ( ^caracu acaract )n from the regression function determined from the characteristic couplets of the pulses preceding the pulse in question fcara(.t , exceeds a predetermined threshold distance.

[0180] The processing unit may also be capable of determining, at the end of each pulse n, a correlation indicator of the regression function, in particular the coefficient of determination R2 of the regression function /

[0181] In this case, the processing unit rejects or weights the characteristic couplet (G caract' acaract)n of the considered impulse n according to the value of the correlation indicator of the regression function f„ determined at the end of impulse n° J caractfl r considered.

[0182] The processing unit can for example reject the characteristic couplet (caract acaract )n of an impulse n if the value of the correlation indicator of the regression function f. . determined at the end of this impulse n is less than a predetermined threshold value.

[0183] The processing unit can also reject the characteristic couplet (Ccat.uct, (icaract)n of a pulse n if the difference between the value of the correlation indicator of the regression function f, determined at the end of the pulse n considered and that of the correlation indicator of the regression function f, determined at the end of the pulse n-1 preceding the pulse n considered exceeds a predetermined threshold value.

[0184] The processing unit can also weight the contribution of the characteristic couplet (Ccaract acaract )n of an impulse n to the determination of the regression function f as a function of the difference between the value of the correlation indicator of the •' caractn regression function ft determined at the end of the considered impulse n and that of the correlation indicator of the regression function f „ determined at the end ° ' caractn\ of the impulse n-1 preceding the impulse under consideration.

[0185] Rejecting or weighting certain characteristic pairs makes it possible to eliminate or limit the influence of certain outliers, which may affect the representativeness of the regression function determined fcaract with respect to the torque / angle characteristic of the screw element.

[0186] 6.2.4. Example of application of the representative function of a characteristic torque / angle of the screw element i. Various uses of the function

[0187] The curve thus obtained by the processing unit is, as previously indicated, representative of a torque / angle characteristic of the screw element, in particular representative of the stiffness of the screw element.

[0188] It may, for example, be taken into consideration:

[0189] - by an operator, in particular the user of the screwing device, to provide him an image of the torque increase of the assembly as a function of the angle;

[0190] - to establish the stiffness curve of the assembly.

[0191] The stiffness curve of the assembly is likely to be taken into account for:

[0192] - the control of the tool;

[0193] - reporting (alerting on the stiffness of a joint which is not that expected);

[0194] - curve processing (machine learning, etc.)

[0195] ii. Exploitation of the function to stop a screwing tool at the end of a screwing operation

[0196] The function obtained according to the invention by the processing unit can be used to stop the screwing device at the end of a screwing operation.

[0197] In this case, the processing unit implements, during at least part of the pulses, a step of determining at least one useful angle value autilen representative of a state of progress of the screwing of the element to be screwed at the end of the pulse n considered.

[0198] The useful angle value autilen is for example the maximum angle value reached during the impulse n considered.

[0199] The processing unit then implements a step of determining a theoretical tightening torque value Cth reached at the end of the impulse n from at least one useful angle value autîlen and the function f

[0200] To do this, it calculates the theoretical tightening torque by applying the function determined at the useful angle: / Y

[0201] The controller then implements the following steps:

[0202] - a step for detecting the attainment of a predetermined screw-stopping criterion;

[0203] - a step of stopping the motor when the screwing stop criterion is reached.

[0204] In addition, the processing unit implements a step of comparing the theoretical tightening torque value of the considered impulse n with a predetermined target torque value, the predetermined screwing stop criterion being a function of the result of this comparison.

[0205] Reaching the predetermined screw-stopping criterion corresponding to an exceedance of the predetermined target torque value by the theoretical torque value Cthn-

[0206] More specifically, for example, the processing unit can determine, at the end of each pulse, the useful angle autilen representative of the progress of screwing the element to be screwed at the end of the considered pulse n.

[0207] Then, the processing unit determines the theoretical tightening torque f / j theoretically reached at the end of the impulse n.

[0208] The processing unit then compares, at the end of each pulse n, the theoretical tightening torque Cthn with the predetermined target torque value.

[0209] When the theoretical tightening torque Cth^ exceeds the predetermined target torque value, the controller stops the motor and the screwing operation thus ends.

[0210] In variants, the determination of the useful angle can be triggered at a given moment during screwing, such as when a predetermined screwing torque threshold is reached, when a measured torque threshold is crossed, or otherwise...

[0211] It should be noted that the impulses taken into consideration to determine the useful angle are not necessarily those taken into consideration to determine the couplets used to determine the function f

[0212] For example, we can determine the function fcuract on the first pulses because these are less noisy, and the useful angles can only be determined after several pulses because it is at the end of tightening that we want to determine if the theoretical tightening torque Cth calculated from the useful angle exceeds the target torque.

[0213] This saves calculation time.

[0214] On the other hand, if better accuracy is desired, the function f caractct 'cs anê'cs utiles avtUe will be determined for all the clamping impulses.

[0215] In one variant, the processing unit and the controller may decide to stop a screwing operation in progress after an impulse n before the theoretical tightening torque Cth reaches the target torque in anticipation that the tightening torque reached at the next impulse n+1 will result in excessive over-tightening, i.e. an excessive exceeding of the target torque.

[0216] In one variant, the processing unit and the controller can determine the torque ramp-up slope and adapt the motor power accordingly to obtain the best compromise between screwing time and precision.

[0217] Advantageously, the step of generating the generated couplets (Q ¢^) and the step of determining the function ff can be carried out after the last pulse, during the instant between two pulses. This allows for a relatively long time to perform the calculations.

[0218] The step of generating the generated couplets (Cb a,) can nevertheless also be carried out substantially in real time.

[0219] iii. Use of the function to generate an alert if the stiffness of the assembly being screwed is far from its theoretical stiffness

[0220] The ft function obtained according to the invention by the processing unit can be used to issue an alert if it is detected that the stiffness of the assembly being screwed is too far from its theoretical stiffness.

[0221] To this end, the processing unit can implement a step of comparing the function f determined by the processing unit to a predefined theoretical function aima characteristic of the screwed element. This theoretical function can be determined empirically during tests or by theoretical calculation, and is representative of the theoretical stiffness of the screwed assembly.

[0222] The method then includes a step of issuing an alert by means of alerting integrated into the screwing system when the function fcaract determined by the processing unit is far from the predefined theoretical function beyond a predetermined distance criterion.

[0223] For example, in the case where the characteristic function f determined by the processing unit is an affine (straight) function, if the slope coefficient of this straight line is very different from the slope coefficient of the theoretical (straight) function, for example greater or less than k times the slope coefficient of the theoretical straight line, then an alert signal is issued.

[0224] In the case where the function ft determined by the processing unit is an arbitrary function (i.e., not a linear function), the processing unit may compare certain points of the function f determined by the processing unit and the theoretical function and trigger an alert when these points are too far apart. The processing unit may also compare the area under the curve of the function f determined by the processing unit and the area under the curve of the theoretical function and trigger an alert when these areas are too different. 6.3. Miscellaneous characteristics

[0225] In one embodiment, the method includes a step of generating a curve representing the function / r J caract

[0226] The method may also include a step of exporting the representative curve of the function / to processing and / or storage means screw curves.

[0227] These processing methods can, for example, allow the following to be performed with the curves:

[0228] - analyses

[0229] - comparisons

[0230] - reporting

[0231] - alerts

[0232] -etc...

[0233] These processes can be carried out by an operator, or by computer, in particular via machine learning algorithms.

[0234] In the preferred embodiment described above, the function fcuruct is determined from the characteristic couplets (CEaract, 0^^) determined at least for certain impulses. However, alternatively, the function fcaract can be determined directly from the generated couplets (Q.H could, for example, be directly from a regression of certain selected generated couplets, a function defining the envelope curve of the generated couplets, etc.

[0235] The different embodiments and variants described in this document can be combined.

Claims

Demands

1. A screw-driving system comprising a device for pulsed screwing of a screw-element, said screw-driving device comprising at least: - a motor; - an output shaft capable of being driven in rotation by said motor; - angle measuring means capable of measuring at least one quantity representative of the angle of rotation of said output shaft; - torque measuring means capable of measuring at least one quantity representative of the tightening torque delivered by said output shaft; said system further comprising: - a controller of said motor capable of controlling said motor so that said output shaft delivers a plurality of successive screw-driving pulses capable of being transmitted to said screw-element;- a processing unit capable of generating generated torque / angle pairs, each generated pair comprising a torque value and an angle value recorded simultaneously by said torque measurement means and by said angle measurement means during at least a part of said pulses, characterized in that said processing unit is capable of determining, from at least some of said generated torque / angle pairs, a function representative of a torque / angle characteristic of said screw element.;

2. A screwing system according to claim 1 in which said processing unit is capable of determining, for each pulse of said at least a part of the pulses, at least one characteristic torque / angle couple of said pulse, each characteristic couple being determined from said generated couplets (i.e. selected from or calculated from), said function being determined from said characteristic couplets determined for each pulse of said at least a part of the pulses.

3. A screw-tightening system according to claim 2, wherein said processing unit is capable of generating said function by determining a regression function of at least a portion of said couplets characteristics determined at each pulse of said at least a part of the pulses.

4. Screwing system according to claim 3 wherein said processing unit is capable, at the end of each pulse of said at least a part of said pulses, of rejecting or weighting said at least one characteristic couplet of the pulse considered, for the determination of said regression function.

5. Screwing system according to claim 4 wherein said processing unit is capable of rejecting said at least one characteristic couplet of said impulse when the distance of said at least one characteristic couplet from the regression function determined from the characteristic couplets of the impulses preceding said impulse in question exceeds a predetermined threshold distance.

6. Screwing system according to any one of claims 1 to 5 wherein said processing unit is capable of determining, during at least one of said pulses, at least one useful angle value representative of a state of progress of screwing said element to be screwed at the end of said pulse.

7. Screwing system according to claim 6 in which said processing unit is capable of determining a theoretical tightening torque value reached at the end of said impulse from said at least one useful angle value and said function.

8. Screwing system according to claim 7 in which said controller is capable of: - detecting the attainment of a predetermined screwing stop criterion; - stopping said motor when said screwing stop criterion is reached; said processing unit being capable of comparing said theoretical tightening torque value of the considered impulse with a predetermined target torque value, said predetermined screwing stop criterion being a function of the result of this comparison.

9. Screwing system according to claim 8 wherein the achievement of said screwing stop criterion consists of exceeding said predetermined target torque value by said theoretical torque value.

10. A screw-screwing system according to any one of claims 1 to 5, wherein said processing unit is capable of performing said function determined to a predefined theoretical function characteristic of said screwing element, said screwing system including warning means, said warning means being capable of issuing a warning when said determined function is far from the predefined theoretical function beyond a predetermined distance criterion.

11. A method for pulse-driven screwing of a screw-in element by means of a pulse-driven screw-in system according to any one of claims 1 to 10, said method comprising at least: - a step of driving said motor by said controller so that said output shaft delivers a plurality of successive screw-in pulses to said screw-in element; - a step of measuring by said angle-measuring means a quantity representative of the angle of rotation of said output shaft; - a step of measuring by said torque-measuring means a quantity representative of the tightening torque delivered by said output shaft;- a generation step by said processing unit of generated torque / angle pairs, each generated pair comprising a torque value and an angle value recorded simultaneously by said torque measurement means and by said angle measurement means during at least a part of said pulses, characterized in that said method comprises a determination step by said processing unit, from at least some of said generated torque / angle pairs, of a function representative of a torque / angle characteristic of said screw element.;

12. A screwing method according to claim 11 comprising a step of determining by said processing unit, for each pulse of said at least a part of said pulses, at least one characteristic torque / angle couple of said pulse, each characteristic couple being determined from said generated couples, said function being determined by said processing unit during said determination step from said characteristic couples determined for each pulse of said at least a part of said pulses.

13. A screwing method according to claim 12, wherein said step of determining said function comprises a step of generation by said processing unit of a regression function of at least a part of said characteristic couplets determined at each pulse of said at least a part of said pulses.

14. Screwing method according to claim 13 comprising, at the end of each pulse of said at least a part of said pulses, a rejection or weighting step by said processing unit of said at least one characteristic couplet of the pulse considered, with a view to determining said regression function.

15. A screwing method according to claim 14 wherein said processing unit is capable of rejecting said at least one characteristic couplet of said impulse when the distance of said at least one characteristic couplet from the regression function determined from the characteristic couplets of the impulses preceding said impulse in question exceeds a predetermined threshold distance.

16. A screwing method according to any one of claims 11 to 15 comprising, during at least a part of said pulses, a step of determining by said processing unit at least one useful angle value representative of a state of progress of the screwing of said element to be screwed at the end of said pulse.

17. A screwing method according to claim 16 comprising a step of determining by said processing unit a theoretical tightening torque value reached at the end of said impulse from said at least one useful angle value and said function.

18. A screwing method according to claim 17 comprising: - a step of detection by said controller of the attainment of a predetermined screwing stop criterion; - a step of stopping said motor by said controller when said screwing stop criterion is reached; said method further comprising a step of comparison by said processing unit, of said theoretical tightening torque value of the considered impulse with a predetermined target torque value, said predetermined screwing stop criterion being a function of the result of this comparison.

19. A screwing method according to claim 18 in which said achievement of said predetermined screwing stop criterion corresponding to an exceedance of said predetermined target torque value by said theoretical torque value.

20. A method according to any one of claims 11 to 15 comprising a step of comparing, by said processing unit, said determined function to a predefined theoretical function characteristic of said screw element, and a step of issuing an alert by said alerting means when said determined function is far from the predefined theoretical function beyond a predetermined distance criterion.

21. Product computer program comprising program code instructions for implementing a method according to any one of claims 11 to 20 when executed by a processor.

22. Computer-readable recording medium comprising program code instructions which, when executed by a processor, cause the processor to implement a method according to any one of claims 11 to 20.

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