JP2018108639A - Method for controlling electric impulse screw driver according to motor instantaneous rotation frequency, and device adapted to method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize an operation of a motor of a discontinuous or continuous electric impulse screw driver device.SOLUTION: In a method for controlling a discontinuous screw driver device which comprises an electric motor, and in which a rotor of the electric motor is connected to a terminal unit which can be rotationally driven, and the motor is supplied with power by sequential power supply voltage pulses, the method includes a step for acquiring an instantaneous power supply voltage of the motor between the power supply voltage pulses, and the step includes at least the following steps of: a first step for measuring an instantaneous rotation frequency of the rotor at a real time; a second step for acquiring a component of a voltage of the power supply voltage pulse being a second step in which the component is decided by the instantaneous rotation frequency; and a third step for acquiring the voltage of the power supply voltage pulse which is incorporated with a voltage value according to the instantaneous rotation frequency of the rotor.SELECTED DRAWING: Figure 12

Description

1. The field of the invention is the field of methods for driving such screwdrivers, as well as the design and manufacture of electric impulse or pulse mode screwdrivers.

2. Prior art Screwing devices or screwdrivers are commonly used to tighten assemblies in various industrial sectors, for example in the assembly of automobiles.

There are essentially two known types of electric screwdrivers:
-A continuous tightening screwdriver device;
-Discontinuous or intermittent pulse mode or impulse screwdriver;
There is.

  These two types of screwdriver devices have very similar mechanical architectures, but are distinguished from each other by their power supply mode in particular.

  The continuous tightening screw driver device is permanently supplied with a constant voltage or a non-constant voltage during a continuous tightening screw tightening operation until a desired tightening torque is obtained.

  During the impulse screwdriver tightening operation, the impulse (or pulse mode) screwdriver device is powered by successive voltage pulses until the desired tightening torque is obtained. Therefore, these motors are discontinuously powered to generate sequential torque pulses rather than long-term and continuous torque increases on the screws. This reduces the reaction torque of the tool as perceived by the operator.

  The present invention relates in particular to the impulse screwdriver device described in more detail herein. Such a screw driver device is described in, for example, Patent Document 1 filed by the present applicant.

  The electric impulse screwdriver device or screwdriver is usually provided with a transmission system with play of play between the motor and the rotary terminal unit that can be screwed. During the screw tightening phase, the motor is sequentially powered by electrical pulses. With each electrical pulse, the motor rotor accelerates and eliminates transmission system play in the direction or direction of screwing. When this play is eliminated, an impact is generated in the transmission system. Accordingly, the rotor transmits torque pulses to the screw in cooperation with the terminal unit, and rotationally drives the terminal unit. Then, the rotor bounces back to the transmission system and moves back to the maximum retracted position, where transmission play is eliminated in the opposite direction of the screw tightening direction.

  During the screw tightening phase, several impact cycles are repeatedly performed according to a given frequency until the screw is tightened with the desired tightening torque.

Referring to FIG. 1, which shows the characteristics of pulses with respect to electrical commands, motor rotational frequency, and electromagnetic torque provided by a screwdriver, each impact cycle includes:
-Step 1: An electrical pulse for supplying power to the motor, causing free acceleration of the rotor, during which the rotor eliminates play in the transmission system in the direction of screwing.
-Step 2: The impact of the rotor in the transmission system, during which the torque pulse is transmitted to the terminal unit when the clearance is eliminated.
-Step 3: Reset the system by natural rebound of the rotor, causing the rotor to return to its maximum retracted position by eliminating play in the direction of screw loosening.

Accordingly, the rotor is movable between the following positions.
The maximum retracted position in which the play in the transmission system is maximum in the screwing direction. This position is achieved when the output shaft and grip of the screwdriver are fixed and the motor rotor is fixed against the transmission system at the end of rotation in the reverse direction of screw tightening. System play is eliminated in the direction or direction of unscrewing.
An impact position where play is eliminated in the screwing direction; This position is achieved when the output shaft and grip of the screwdriver are fixed and the motor rotor is fixed against the transmission system at the end of rotation in the screwing direction. Play is eliminated in the screwing direction.

  During the transition from its maximum retracted position to its impact position, the rotor accumulates kinetic energy during acceleration to eliminate play in the transmission system. When this play is eliminated, the rotor transmits this kinetic energy to the screw via a transmission system during the torque pulse.

  Now look at step 1 more closely. This step attempts to store energy that is partially transmitted to the screw in the form of potential energy for tightening at the moment of impact.

The mechanical potential energy is given by the following simplified formula:
Where
J is the inertia of the moving part (rotor + transmission system).
ω is the rotational frequency of the motor rotor along its longitudinal axis.

  During the impulse screwing operation, the acceleration phase in each pulse must be very high considering the available angular acceleration travel distance. And it is necessary to make maximum use of the acceleration capability of the motor and its power supply.

  In continuous screwdriver devices, there is no need for this high acceleration.

  The electric impulse screwdriver device implements a drive mode known as an “open loop” mode during the rotor acceleration phase, which is based on a predetermined “template” of the setpoint power supply voltage as a function of time. Depends on the set value of the power supply voltage. Such a template allows adjustment of the power supply voltage during the acceleration phase. However, it does not consider the effect on the actual (or instantaneous) rotational frequency of the motor. Such a template consists of a correspondence table associating multiple pairs of power supply voltage values and moments.

  This template is required in the laboratory for a typical screwdriver device and for a given screwdriver operation. It is then registered in a controller that performs the drive of the screwdriver and is used in production to drive the motor power in a timely manner to perform a predetermined screwdriver operation.

FIG.
An example of such a template (voltage template) representing the motor supply voltage as a function of time,
The transition of the current consumed by the motor as a function of time,
-Indicates the variation in the rotational frequency of the motor during the power pulse.

In FIG. 2, the following can be understood.
The power supply voltage is constant at every moment of the power pulse.
-There is a current spike when the motor starts, and then there is a gradual drop in current during motor acceleration.
A reduction in the gradient of the rotational frequency between electrical pulses, in other words a decrease in the acceleration (the rotational frequency graph has been bent slightly inward due to the reduction of the directivity factor over time).

  The reason for this decrease in acceleration during the electrical pulse is as follows.

  The assembly formed by the screwdriver device and its controller, referred to as the screwdriver system, is limited by design so that its capability carries a maximum current equal to, for example, 75 amps. Exceeding this maximum current leads to a shutdown of the controller, which requires action by a maintenance technician to be able to resume the controller in order to maintain the screwdriver device.

Therefore, the amplitude of the power supply at low rotational frequency (when starting) is Ohm's law U _max = R. Limited by this maximum allowable current according to I _max , U _max is the maximum allowable power supply voltage, I _max is the maximum allowable current, and R is the resistance of the system formed by the screwdriver device and its controller.

  Therefore, the setpoint voltage template is limited by this maximum allowable amplitude.

  Here, when the rotational frequency of the rotor rises, the motor generates a voltage called counter-electromotive force or back electromotive force, the value of which is proportional to the rotational frequency, Subtracted from motor supply voltage. Thus, the payload voltage tends to drop during the electrical pulse. This reduces the current consumed by the motor, as observed in the graph, and thus reduces the instantaneous electromagnetic torque.

  This therefore greatly limits the rotational frequency that can be achieved by the motor at the end of the electrical pulse, and thus the kinetic energy that the controller can provide to the screwdriver during that pulse as the rotational frequency increases. Is done.

  Here, this limitation of the kinetic energy that can be transmitted to the screw limits the screw driver's tightening ability, which can hardly be compensated for by increasing the angular acceleration travel distance, which is This is because the travel distance itself is limited by play in the gear reduction system or generally by play in the motion chain between the motor and the screw.

A constant set voltage is applied during the power pulse, and
-Maximum current limit,
A decrease in payload voltage resulting from an increase in back electromotive force during the electrical pulse,
In order to overcome these disadvantages of the prior art resulting from, a voltage template that has become non-constant and changes over time has been developed. Such a template is shown in FIG.

  As can be seen, the voltage template has a low initial value, which then increases over time.

With this form of template, the following is noted.
-The low initial value of the supply voltage reduces the current spike when starting, thus avoiding the controller exceeding the maximum allowable current and shutting down the controller when starting the device.
-The gradual increase of the power supply voltage after the start phase makes it possible to compensate for the increase of the counter electromotive force due to the rotational frequency and to obtain a constant current during the motor power supply period.

  Therefore, the use of a voltage template with a variable power supply has a more constant electromagnetic torque, i.e. it does not decrease when the motor's rotational frequency increases, and there is no risk of shutting down the controller for a longer period of time. The effect is to generate a more stable acceleration of the motor, which makes it possible to achieve torque.

  According to another aspect, and depending on the suitability of the assembly and the target level of torque, it may be useful to adjust the level of kinetic energy at the end of the electrical pulse and thus prior to the impact. For this purpose, the template is set for the application that requires the strongest pulses, and for applications that require lower screwing forces, i.e. with low flexibility and the required tightening torque. A relaxation factor (referred to as “pulse amplitude”) is applied to this basic template for lower assembly. For example, if the usage situation requires 60% of the output of the basic template, a similarity transformation in 60% of the basic template is achieved.

Thus, the formula used to determine the voltage applied at a given moment (t) is
Where
U (t) is the voltage applied at the instant (t).
TabTemplate [t] is a table that contains all the points of the desired template and is indexed as a function of the moment (t).
PulseAmplitude is a coefficient of amplitude in the range of 0-1.

  A template in about 60% of the basic template shown in FIG. 3 is shown in FIG. In this figure, it can be seen that the application of similarity transformation does not allow the current consumed by the motor during the pulse to be maintained at a significantly constant level. Therefore, similarity transformation cannot be used to obtain a constant motor torque and a stable acceleration that does not decrease as the motor's rotational frequency increases.

  Thus, apart from the case of the basic template, the template set in consideration of the transition of the power supply voltage of the motor with time does not consider the decrease in voltage that is really necessary for the motor. It does not compensate for a decrease in current applied to the motor, a decrease in electromagnetic torque, and thus a decrease in rotor acceleration.

  Therefore, a simple variation of the supply voltage setting as a function of time is not sufficient, as it only works for a given case (when used to set the basic template) This is because the template does not cover all other possible use cases adapted by similarity transformation.

  FIG. 5 is consumed by the motor during the implementation of the template of FIG. 3 in a situation where the rotor of the motor is shut off before the end of the pulse (rotational frequency decreases before the end of the power supply voltage pulse). Fig. 4 shows the variation of current and rotor rotational frequency as a function of time. This motor rotor shut-off can occur when the play available in the transmission system for free acceleration of the rotor is preabsorbed prematurely before the motor power pulse is completed. .

  In this case, when the rotational frequency of the motor decreases due to the interruption received by the motor, a significant increase in current (current or intensity) consumed by the motor is observed. Thus, the useful voltage for the motor is large compared to its rotational frequency, and thus the current rises beyond the limits acceptable by the system. This can lead to failures that stop the screwing operation and activate the safety system that shuts off the controller due to exceeding the maximum current allowed by the system, which impairs productivity. Therefore, it is unacceptable in an industrial screw tightening environment.

  Therefore, the use of the power supply voltage template as a function of time according to the prior art does not make it possible to drive the exact same type of screw tightening device in different usage situations, without causing the controller to shut down. Unable to cope with abnormalities that may occur during the tightening operation (rotor shut-off, passage of hard points during assembly, etc.), restarting the controller necessitates actions by maintenance technicians And therefore unacceptable at the industrial level because it takes time.

  Therefore, the driving of the electric impulse screw tightening device can be further improved.

International Publication No. 2012/143532

3. Objects of the invention The present invention aims in particular to provide an efficient solution to at least some of these various problems.

  In particular, according to at least one embodiment, an object of the present invention is to optimize the operation of the motor of a discontinuous or intermittent electric impulse screwdriver device.

  In particular, according to at least one embodiment, an object of the present invention is to enable a motor to generate a substantially constant electromagnetic torque through each power supply voltage pulse.

  According to at least one embodiment, another object of the present invention is to allow a motor to generate high electromagnetic torque without causing any risk of exceeding the maximum current allowable by the screwdriver system. It is.

  The present invention also does not cause interruption of the operation of the screwdriver system, in at least one embodiment, and in particular does not generate any excessive current if the power source persists even if play in the motion chain is eliminated. Pursuing the purpose of dealing with abnormal operation.

  Another object of the present invention is to adapt the basic template to different usage situations by the principle of similarity transformation in at least one embodiment without reducing the performance level.

4). To this end, the present invention comprises an electric motor, and the rotor of the electric motor is connected to a terminal unit that can be driven to rotate, and the motor is powered by sequential power supply voltage pulses. A method for controlling a discontinuous screwdriver device is proposed.

According to the present invention, such a method includes determining an instantaneous power supply voltage of the motor during each of the power supply voltage pulses, which comprises at least the following steps:
-A first step of measuring the instantaneous rotational frequency of the rotor in real time;
-A second step in determining the voltage component of the power supply voltage pulse, the component being determined by the instantaneous rotational frequency;
And a third step of determining in real time the voltage of the power supply voltage pulse incorporating the voltage value in accordance with the instantaneous rotation frequency of the rotor.

  Therefore, according to this aspect, the present invention incorporates the voltage of each power supply voltage pulse of the motor of the intermittent or discontinuous tightening screw driver device into this voltage, a component whose value depends on the rotational frequency of the rotor of the motor. Is what you want.

  Compensates for the back electromotive force, which increases with the motor's rotational frequency and is subtracted from the voltage consumed by the motor to generate electromagnetic torque, by considering the rotor's rotational frequency to determine the voltage of each power supply voltage pulse can do.

  Thus, according to the present invention, it is possible to obtain a more constant current during the period of power supply of the motor, and therefore it is possible to prevent a decrease in electromagnetic torque and thereby the acceleration of the rotor.

  The present invention also produces high electromagnetic torque without incurring any risk of exceeding the maximum current allowable by the screwdriver system by obtaining the voltage variation of the power supply voltage pulse as a function of motor rotational frequency. It becomes possible. In practice, the voltage of the power supply voltage pulse is low enough not to promote exceeding the maximum current allowable by the system when starting, and then the rotor's rotational frequency causes the electromagnetic frequency due to this rotational frequency to increase. It can be gradually increased to compensate for the loss of torque and thus ensure that a high level of electromagnetic torque is achieved.

  Thus, the present invention optimizes the operation of the motor of the intermittent or discontinuous electric impulse screwdriver device.

  According to one possible advantageous feature, the component is selected from a predetermined set of voltage values as a function of the instantaneous rotational frequency.

  In this case, since various types of screw driver devices are implemented to perform various types of screw driver operations, the various rotational frequencies of the rotor, the loss of electromagnetic torque due to the increase of the rotational frequency of the rotor, Laboratory tests are performed to determine the values of components that can be compensated for screw driver operations, or screw driver operations that require the maximum amount of energy. These data are recorded on the screwdriver device and selected during parameterization of the screwdriver device according to its type and the type of screwdriver operation to be achieved before it is used in production can do.

  According to another possible advantageous feature, the component is determined as being equal to the product of the instantaneous rotational frequency with a predetermined factor.

  In this case, the component values are not selected but are calculated in real time.

According to one possible advantageous feature, the voltage of each of the supply voltage pulses is
A first term corresponding to a predetermined theoretical constant power supply voltage multiplied by a pulse amplitude factor;
-Corresponds to the sum of the second term corresponding to the component determined by the instantaneous rotational frequency of the rotor.

  The voltage of each power supply voltage pulse corresponds to the sum of a theoretical constant power supply voltage required to reach a predetermined rotational frequency at the time of starting the motor and a dependent component of the rotational frequency. This component makes it possible to compensate for the increase in voltage generated by the counter electromotive force due to the rotational frequency of the rotor, and to obtain a more constant current, that is, electromagnetic torque while power is supplied to the motor.

  The theoretical voltage value of the first term is multiplied by a pulse amplitude factor that can preferably vary between 0 and 1.

  Then, for a given type of screw tightening device, it is possible to determine a unique value for the theoretical constant power supply voltage in the laboratory and for the type of screwdriver operation that requires maximum power. In order to adapt this theoretical value to operation with a smaller required output, the most severe case theoretical value is multiplied by an amplitude factor. Thus, if the screw driver operation being performed requires only 80% of the power required for screw driver operation under the most severe conditions, the amplitude factor will be equal to 0.8.

  By applying this amplitude factor only to the first constant term, not the second term, which is variable as a function of rotor rotational frequency, any type of screwdriver operation is consumed by the motor. There is a constant current to ensure that electromagnetic torque is maintained.

  Preferably, the predetermined theoretical constant power supply voltage is equal to a product of a predetermined value of the current multiplied by the electric resistance of the screwdriver device.

  Preferably, the second term is a voltage value equal to a product of the instantaneous rotational frequency of the rotor and a coefficient of the counter electromotive voltage of the motor.

  According to a possible preferred feature, the second term takes into account data stored in the form of a correspondence table associating a plurality of pairs of power supply voltage values and rotation frequency values of the rotor.

  The execution of the method is then faster as long as it uses the recorded data rather than performing a calculation to determine the second term.

  According to one possible advantageous feature, the method according to the invention comprises the steps of detecting an abnormal operation and correcting the voltage of the power supply voltage pulse of the motor following the detection of the abnormal operation.

  Abnormalities can occur during screwing or unscrewing operations, especially when the play in the transmission system is corrected before the end of the motor supply voltage pulse, the rotor can be shut off There is sex. Thereby, the maximum value of the current allowable by the screw driver device will be exceeded, and this screw driver device may be shut off.

  To overcome this problem, the technique of the present invention detects the occurrence of an anomaly and, accordingly, corrects the motor's power supply impulse voltage to maintain the current below the maximum allowable by the screwdriver device. suggest. Thus, this technique avoids the need to shut off the motor and production line and avoids the need for an act by a service technician to operate it again.

In this case, the above-described step of detecting an operation abnormality is preferably
Measuring the current consumed by the motor;
-Comparing the measured value of the current consumed by the motor with a predetermined threshold;
-Reducing the voltage of the power supply voltage impulse of the motor when the measured value of the current consumed by the motor is greater than or equal to the threshold value.

  According to a preferred variant, the step of reducing the voltage of the power supply voltage pulse of the motor is to reduce the first term of the voltage of the power supply voltage pulse.

  This effectively prevents the maximum value of current allowable by the screw driver device from being exceeded.

  According to another preferred variant, said step of reducing said voltage of said power supply voltage pulse of said motor reduces the sum of the product of said amplitude factor of said first term and said second term. It is in.

  This further prevents the maximum allowable current by the screwdriver device from being exceeded more quickly.

  The present invention also provides intermittent or discontinuous screwing comprising an electric motor whose rotor is connected to a terminal unit that can be driven to rotate, and means for powering the motor by sequential power supply voltage pulses. About the system.

Such a system is a means for determining the instantaneous power supply voltage of the motor during each of the power supply voltage pulses, at least,
-Means for measuring the instantaneous rotational frequency of the rotor in real time;
Means for determining a voltage component of the power supply voltage pulse, the component being determined by the instantaneous rotational frequency;
-Means for obtaining the power supply voltage pulse incorporating the voltage value in real time according to the instantaneous rotation frequency of the rotor.

According to one possible advantageous feature, the means for determining the voltage of the power supply voltage pulse in real time comprises:
A first term corresponding to a predetermined theoretical constant power supply voltage multiplied by a pulse amplitude factor;
Means for calculating the sum of the second term corresponding to the component determined by the instantaneous rotational frequency of the rotor;

  According to one possible advantageous feature, the system according to the invention comprises means for detecting an operational abnormality and means for correcting the voltage of the power supply voltage pulse of the motor following the detection of the operational abnormality.

In this case, the means for detecting an operation abnormality is preferably
-Means for measuring the current consumed by the motor;
Means for comparing the measured value of the current consumed by the motor with a predetermined threshold;
-Means for reducing the voltage of the power supply voltage pulse of the motor when the measured value of the current consumed by the motor is greater than or equal to the threshold value;

  According to one possible advantageous feature, the means for reducing the voltage of the power supply voltage pulse of the motor reduces the first term of the power supply voltage pulse.

  According to another possible advantageous feature, said means for reducing the voltage of said power supply voltage pulse of said motor reduces the sum of the product of said amplitude factor of said first term and said second term. Let

  The invention also relates to a computer program product comprising program code instructions which, when the program is executed on a computer, implements the method according to any one of the above variants.

  The present invention also relates to a computer-readable non-transitory storage medium storing the computer program product described in the above-described modification.

5. List of Figures Other features and advantages of the present invention will become more apparent from the following description of the preferred embodiment and the accompanying drawings, given as a simple illustrative and non-exhaustive example.

FIG. 6 shows the pulse shape for intermittent, discontinuous tightening screwdriver commands, torque and rotational frequency. It is a figure which shows the shape of the time related template of the constant voltage by a prior art. It is a figure which shows the time related template of the non-constant voltage by a prior art. It is a figure which shows the time related template of the non-constant voltage by a prior art. It is a figure which shows the time related template of the non-constant voltage by a prior art. It is a figure which shows the screw driver of an example of the screw driver system by this invention. It is a figure which shows the controller of an example of the screw driver system by this invention. FIG. 11 shows one of the two terms of the template formed by the invention shown in FIG. FIG. 11 shows one of the two terms of the template formed by the invention shown in FIG. It is a figure which shows the template formed by this invention. FIG. 13 schematically shows the adjustment principle of the method according to the invention shown in the form of a flow chart in FIG. Fig. 2 shows a method according to the invention in the form of a flowchart. FIG. 4 is a diagram showing various shapes of power supply voltage pulses according to the present invention. FIG. 4 is a diagram showing various shapes of power supply voltage pulses according to the present invention. FIG. 4 is a diagram showing various shapes of power supply voltage pulses according to the present invention. FIG. 4 is a diagram showing various shapes of power supply voltage pulses according to the present invention. It is a flowchart of the safety system with respect to the power supply by this invention when an operation abnormality is detected. It is a figure which shows the principle of the power supply voltage pulse in the case of a simple safety mechanism (security). It is a figure which shows the shape of the power supply voltage pulse in the case of a simple safety mechanism. It is a figure which shows the principle of the power supply voltage pulse in the case of a reinforced safety mechanism. It is a figure which shows the shape of the power supply voltage pulse in the case of a reinforced safety mechanism.

6). Description of specific embodiments 6.1. TECHNICAL FIELD The present invention is applied to a screw driver device or an electric screw driver called an intermittent or discontinuous screw driver tightening device.

  Referring to FIG. 6, this type of screw driver 1 usually includes a casing 10 that houses an electric motor 11 provided with a stator 110 and a rotor 111. The rotor 111 is connected to the terminal unit 13 by means of a transmission system 12 with operational play, the terminal unit 13 being driven in rotation and in cooperation with the screw, the screw is tightened or loosened during the assembly operation. Can be ensured.

  As described in the section dealing with the prior art, the motor of such a screwdriver device is powered by successive power supply voltage pulses.

  The example described herein is constituted by a screwdriver 1 connected to a controller 2 by a cable, and the controller 2 itself is connected to a company power network. This controller allows control of the operation of the screwdriver and its power supply.

  In one variation, the energy source can be a battery secured to the screwdriver, in which case the controller is miniaturized and incorporated into the screwdriver so that the screwdriver is self-supporting.

The screwdriver is connected to the controller by:
A power cable 21 for the motor;
A transceiver module 22 that allows the screwdriver and controller to communicate with each other by cable or wirelessly, if necessary, with other devices such as a computer network. Thus, the screwdriver can receive command signals from the controller, and the controller can receive signals coming from various sensors built into the screwdriver.

  According to the exemplary embodiment shown in FIG. 7, the controller 2 comprises a random access memory 23 (RAM) and a processing unit 24, which comprises a processor, for example, for carrying out the driving method according to the invention. This program is driven by a computer program including program code instructions, and this program is stored in a read only memory 25 (ROM). The controller typically includes an input / output interface 26 that specifically validates the program, and possibly a screen 27 and information input means such as a keypad or mouse 28. The controller comprises a power supply 29 for the motor 11 and a sensor 30 that detects the current consumed by the motor 11, usually located in the motor phase.

  At initialization, the code instructions of the computer program are loaded, for example, into the random access memory 23 and executed by the processor of the processing unit 24. The random access memory 23 contains in particular suitable formulas for calculating the various variables that are determined during the application of the method. The processor can then drive the screwdriver device accordingly.

  FIG. 7 shows several possible configurations in which the controller is configured to perform the steps of the driving method according to the invention (in any one of the various embodiments, or in a combination of these embodiments). One particular method is shown. In practice, these steps may be performed by a reprogrammable computer machine (PC computer, DSP processor or microcontroller) executing a program containing a sequence of instructions, or a set of dedicated computing machines (eg, FPGA or ASIC). Logic gates, or any other hardware module).

  If the controller consists of a reprogrammable computing machine, the corresponding program (ie, sequence of instructions) can be a removable storage medium (eg, floppy disk, CD-ROM or DVD-ROM) or non-removable Storage medium, which can be read in part or in whole by a computer or processor.

  The system conventionally comprises means for real-time measurement of the instantaneous rotational frequency of the rotor, comprising an angle sensor 14 incorporated in the screwdriver device at the rotor shaft. Such an angle sensor may comprise a set of magnets fixedly attached to the rotating rotor, for example, in a manner known per se, when the rotating rotor rotates in front of the Hall effect sensor. Depending on the position of the rotor, the assembly composed of magnets and Hall effect sensors generates an electrical signal whose level represents the position of the rotor. Measuring means for measuring the rotational frequency of the rotor derives the position of the rotor with respect to time in order to determine the rotational frequency.

  The screwdriver controller and the various sensors constitute various means for carrying out the steps of the driving method according to the invention, as can be seen in more detail in the following description of the driving method according to the invention.

6.2. General Principle The present invention incorporates the value of the motor pulsed instantaneous power supply voltage during the rotor acceleration phase of the discontinuously tightened screwdriver device and incorporates into this value a component whose value is determined by the instantaneous rotational frequency of the motor rotor. Can remind you of what you want to do.

In this embodiment, the formula relating voltage, current and rotational frequency is:
Where
U is a voltage (volt) applied to the motor.
I is a current (ampere) applied to the motor.
ω is the rotational frequency (rpm) of the motor.
R is the electrical resistance (control electronics, cable and motor) of the screwdriver device.
Ψ is a counter electromotive voltage coefficient of the motor.

  In a permanent magnet synchronous motor, the torque supplied by the motor is proportional to the current.

  Thus, a given level of torque has a corresponding level of current I. Because the current is established at this level at the start of motor acceleration, i.e., at zero rotation frequency, the motor supply voltage is R.D. Should be equal to I. In order to take full advantage of the tightening capability of the system, the level of current can be the maximum level of current that the system can withstand.

  As the rotational frequency increases, the back electromotive force increases. In order to maintain the electromagnetic torque and thus the current consumed by the motor at its maximum level Imax, the motor supply voltage must be increased by the value of the back electromotive force voltage.

  Therefore, by taking into account the rotor rotational frequency to determine the value of the instantaneous power supply voltage of the motor, it is possible to compensate for the back electromotive force that increases with the motor rotational frequency, and therefore, during each pulse Torque and constant current can be obtained.

The set value of the voltage of each power supply voltage pulse is
A first term corresponding to a predetermined theoretical constant power supply voltage multiplied by a pulse amplitude factor;
-Corresponds to the sum of the second term corresponding to the component determined by the rotational frequency.

In this embodiment,
The first term of the voltage is a constant value that determines the level of current consumed by the motor at zero rotational frequency. It has the form PulseAmplitude. It can be expressed as Offset. here,
-PulseAmplitude is an amplitude coefficient.
-Offset is the voltage at which the current consumed by the motor at zero rotational frequency is the maximum level of current allowed for the screwdriver system.
The second term compensates for the effect of the back electromotive force and allows the current to be maintained at a constant level during the rotor acceleration phase;

In production, the following two variants can be envisaged.
The first variant consists in performing a real-time calculation of the second term based on a real-time measurement of the rotational frequency of the rotor.
The second variant utilizes a corresponding table pre-recorded in the memory of the controller, which associates a plurality of pairs each containing a power supply voltage value and a value of the rotor rotational frequency (ie added to the power supply voltage) There is to do.

According to a first variant, the value U (t) of the power supply voltage pulse at the instant t is equal to:
ω (t) is equal to the instantaneous rotational frequency of the motor at the instant t.
Ψ is a counter electromotive voltage coefficient of the motor. This parameter, known to those skilled in the art, can be calculated or measured experimentally in the laboratory.

According to the second variant, the value U (t) of the power supply voltage pulse at the instant t is equal to:
Where
Speed (t) is the rotational frequency of the motor at the moment (t).
TabTemplate [Speed (t)] is a table containing the desired set of power supply voltage points indexed as a function of the various rotational frequencies of the rotor. The values in this table can be the results of laboratory experiments.
Offset is the maximum voltage offset appropriate for a screwdriver system.
PulseAmplitude is a coefficient in the range of 0-1.

  Thus, as shown in FIG. 11, driving the motor's power supply therefore adds the offset to the offset as a function of the actual rotational frequency (speed) of the motor (M) based on a predetermined template. This template is in the first case the product Ψ. corresponding to ω (t), and in the second case, for various values of ω (t), the product Ψ. Corresponds to a table listing the results of ω (t).

  There are various types of screw driver systems, each type being characterized in particular by its screw driver transmission system, its dimensions, its efficiency, its motor drive mechanism and the like.

  Each type of screwdriver system can be adapted to implement various screwdriver strategies in production. It is difficult, if not impossible, to parameterize each type of screwdriver system for all screwing operations that tend to be used.

  Thus, each type of screwdriver system is parameterized according to the screwing operation under the most severe conditions that tend to be implemented, i.e. the screwing operation that requires the greatest amount of energy.

6.3. Preliminary parameterization during manufacture of the screwdriver system Each type of screwdriver device must be parameterized before it can be used in production.

  Parameterization is used later in production to drive the motor of each system of the same type, for each new type of screwdriver system implemented for its application under the harshest conditions, whereas Finding the appropriate parameters.

In connection with the first variant, these parameters are:
-Offset and -Ψ.
The Offset is equal to the product of the electrical resistance of the screwdriver system and the maximum allowable current allowed by the system that is shut off when the system is exceeded.

  In connection with the second variant, these parameters further include TabTemplate [Speed (t)], which compensates for the loss of efficiency due to increasing rotor rotational frequency for various rotor rotational frequencies. Including the corresponding value of the additional voltage, which is the product Ψ. Corresponds to table recording equal to ω.

  These values Offset, Ψ and TabTemplate [Speed (t)] can be determined by experiment once at a time, these parameters are appropriate for that type of screwdriver system, It remains unchanged for the lifetime.

  The first term of the power supply voltage pulse can be illustrated, for example, by the graph in FIG. 8 showing the offset voltage as a function of the rotor rotational frequency, which is whatever the value of the rotor rotational frequency. Is also constant.

  The second term of the power supply voltage pulse can be shown, for example, by the graph of FIG. 9 showing the transition of the additional voltage added to the offset voltage as a function of the rotor rotational frequency.

  The value of each power supply voltage pulse sent to the motor corresponds to the sum of the first term and the second term. The graph of FIG. 10 shows an example of this power supply voltage transition as a function of rotor rotational frequency. This example of the graph corresponds to the sum of the graphs of FIGS.

6.4. Preparation for production The parameters (Offset and TabTemplate [Speed (t)]) required to drive the motor of the screwdriver system are recorded in its memory during its manufacture (see § 6.3).

  When a screwdriver system is used in production, it can face variable thickness assemblies, or assemblies that require different levels of torque.

  Therefore, it may be necessary to reduce the tightening force of this screw driver, especially for low tightening torque values. To enable this, the parameter “PulseAmplitude” is selected for each application or assembly to be made. For each particular application, it corresponds to the most severe condition output rate required by this particular application and determines the level of kinetic energy that is stored in the rotor of the motor prior to impact.

  When the screwdriver device is implemented to perform various types of screwing operations, parameters are defined that define the screwing strategy to be applied for each application. These parameters include, among other things, the level of torque to be reached, the pre-screwing speed and the amplitude factor PulseAmplitude. The coefficient PulseAmplitude is determined experimentally by the person in charge of defining the screw tightening strategy.

  These parameters are recorded in the tool's memory and used depending on the application encountered.

6.5. Driving method in production 6.5.1. Normal case: no abnormal operation The driving method according to the invention is carried out during the screwing operation.

  Typically, the screwing operation is performed after actuation by an operator, for example, according to a discontinuous screwing strategy programmed into the controller while the motor is powered by power supply voltage pulses.

  However, during the execution of this screwdriver operation, the present invention implements a specific drive to determine the value of each power supply voltage pulse of the motor. Therefore, such a method is repeated for each pulse by the end of the screwing operation.

  Obtaining each value of the power supply voltage pulse continuously envisages performing step 120 of real-time measurement of the instantaneous rotational frequency ω (t) of the rotor. This is usually done by obtaining a derivative with respect to time for the signal coming from the rotor position sensor.

  Then, during step 121, one component of the value of the power supply voltage pulse determined by the instantaneous rotation frequency is obtained.

  Then, during step 122, a voltage value determined by the rotation frequency is incorporated to obtain the value U (t) of the power supply voltage pulse.

In the case of the first variant, during step 1210, the formula Ψ. A second term of the value of the power supply voltage pulse is calculated from the measured value of the rotational frequency of the rotor according to ω (t). Then, during step 122, the value U (t) of each power supply voltage pulse is calculated by the controller according to the following formula.
The values of PulseAmplitude, Offset and Ψ are in the system's memory. A voltage command is then sent to the motor.

In the case of the second variant, the second term value corresponding to the current rotational frequency is extracted from the table TabTemplate [Speed (t)] recorded in the memory of the controller during step 1211 by Is obtained. Then, during step 122, the value U (t) of each power supply voltage pulse is calculated by the controller according to the following formula.

  FIG. 13 shows the rotational frequency of the rotor during a power supply voltage pulse whose duration is equal to 5 ms in this example, in the case of execution of a screwdriver operation performed under the most severe conditions where the amplitude coefficient PulseAmplitude is equal to 1. It shows the variation between the power supply voltage pulse command for the motor and the current consumed by the motor.

You can see the following.
The speed variation between the supply voltage pulses is completely linear and constant (motor constant acceleration) and not curvilinear as in the prior art.
-The current consumed by the motor is stable.
This is achieved by changing the voltage setting as a function of the rotational frequency of the rotor according to the invention.

  FIG. 14 shows the rotation of the rotor in the course of a supply voltage pulse whose duration is equal to 5 ms in this example, in the case of an application that requires only 30% of the power required for the application under the harshest conditions. It shows the variation in frequency, power supply voltage pulse command, and current consumed by the motor, and the amplitude coefficient PulseAmplitude is equal to 0.3.

  It can be seen that the speed transition is perfectly linear and constant and the current is stable, as in the normal case occurring under the most severe conditions. Changing the offset only affects the final speed obtained at the end of the power supply voltage pulse, and does not compromise the linearity of fluctuations in motor speed or current consumption.

6.5.2. Management of abnormal operation i. Slight Abnormality FIG. 15 shows the rotational frequency of the rotor during a power supply voltage pulse with a duration of equal to 5 ms in this example in the case of the screwing operation performed under the most severe conditions where the amplitude coefficient PulseAmplitude is equal to 1. , Shows the variation in power supply voltage pulse command and current consumed by the motor.

  Here, it can be seen that the rotational frequency is not completely linear (linear and constant), but is perturbed on the contrary. This disturbance results from slight operational abnormalities such as slight variations (friction) of the stiffness of the assembly during tightening, for example. However, the system changes the power supply voltage as a function of the rotational frequency of the rotor to maintain a substantially constant current value.

  Thus, in the event of a slight anomaly, the system corrects the power supply voltage to maintain an acceptable current.

  For certain uses, it is possible that during the screwing or unscrewing operation, the motor may be significantly slowed down or shut off (excessive screwing when passing through a hard point, etc.). is there. This can result in a sudden increase in current, which can exceed the maximum value allowed by the system.

  Such a case is shown in FIG. FIG. 16 shows the rotational frequency of the rotor and the power supply during a power supply voltage pulse whose duration is equal to 5 ms in this example in the case of performing the screwing operation under the most severe conditions where the amplitude coefficient PulseAmplitude is equal to 1. It represents the variation between the voltage pulse command and the current consumed by the motor.

  Here, it can be seen that the motor is “slightly” shut off before the end of the power supply voltage pulse (reduction in rotational frequency at about 0.0065 s).

  This type of interruption appears when play in the transmission system is absorbed before the end of the supply voltage pulse. This may be the result of insufficient rebound of the rotor, so that the rotor cannot return to the maximum retracted position and corresponds to the full value of the angular play of the transmission system. Accelerating travel distance cannot be obtained.

  However, during a decrease in rotational frequency due to rotor shut-off, the system adjusts the power supply voltage to avoid a sudden increase in current.

  However, this method has its limitations because the system is sized to cover slight variations in motor rotational frequency for optimal use.

  However, the basic system cannot prevent the effect of motor shutoff early in the acceleration phase of the power supply voltage pulse. In addition, disturbances that can hardly be modeled, such as the internal resistance of the system, which can fluctuate due to temperature and equipment aging, or problems due to the stability of the voltage of the power grid that also powers the system. There are other cases.

  For example, in order to manage the occurrence of more serious anomalies when the rotor bounce does not occur accurately and when the angular travel distance available for motor acceleration is significantly reduced, Implement a safety system.

ii. More serious abnormality Referring to FIG. 17, the safety mechanism includes a real-time implementation of step 170 for detecting an operational abnormality and step 171 for correcting the value of the power supply voltage pulse of the motor following the detection of the operational abnormality. Become.

More specifically, the step 170 for detecting an abnormal operation and the step 171 for correcting the value of the power supply pulse include the following.
Measuring 1701 the current consumed by the motor in real time;
-Step 1702 comparing the measured value of the current consumed by the motor with a predetermined threshold. This value is preferably equal to the maximum value of current that can be tolerated by the system, for example 75 amps.
Step 1710 of reducing the power supply voltage of the motor when the measured value of the current generated by the motor exceeds a threshold value.

Several types of safety mechanisms, namely
-Simple safety mechanism,
-Enhanced safety mechanism,
Can be implemented.

ii. 1. Simple Safety Mechanism In connection with what is called a simple safety mechanism, the step 1710 of reducing the power supply voltage of the motor is to reduce the first term of the power supply voltage, ie, the offset in this case (step 17101).

  Thus, as shown in FIG. 18, this simple safety mechanism is therefore to limit the offset thoroughly only when an excessively high current is detected for whatever reason.

  FIG. 19 shows the rotational frequency of the rotor and the power supply during a power supply voltage pulse whose duration is equal to 5 ms in this example in the case of performing the screwing operation under the most severe conditions where the amplitude coefficient PulseAmplitude is equal to 1. It represents the variation between the voltage pulse command and the current consumed by the motor. Here it can be seen that the motor is shut off “long time” before the end of the power supply voltage pulse (rotational frequency drop at about 0.0055 s).

  In this case, it is inevitable that the current finally increases. Adjustment of the power supply voltage is not efficient enough to prevent this phenomenon. However, the current safety mechanism can be activated at a threshold to thoroughly limit the setpoint voltage.

  And the performance of the pulse is greatly impaired, which prevents current faults and system interruptions.

  A simple current safety mechanism limits the offset by automatically reducing the coefficient PulseAmplitude applied to the power supply voltage pulse, for example by applying a relaxation factor (e.g. equal to 0.5) determined by experiment can do. As a result, the screwing operation can be terminated without exceeding the maximum current value allowable by the system. This occurs, for example, when the rotor is shut off and / or when an inappropriate power cable is used.

ii. 2. Enhanced safety mechanism If the implementation of the simple safety mechanism is not sufficient, the enhanced safety mechanism can be implemented. In connection with this enhanced safety mechanism, the step 1710 of reducing the motor power supply voltage is to reduce the sum of the product of the amplitude coefficient of the first term and the second term (step 17102).

  As shown in FIG. 20, this enhanced safety mechanism therefore provides a relaxation factor that, for example, is determined experimentally, by adding the offset and additional voltage that varies as a function of rotational frequency when an excessively high current is detected. (E.g., equal to 0.5) is to limit it thoroughly by automatically applying to this sum.

  FIG. 21 shows the rotational frequency of the rotor and the power supply during a power supply voltage pulse whose duration is equal to 5 ms in this example, in the case of performing the screwing operation under the most severe conditions where the amplitude coefficient PulseAmplitude is equal to 1. It represents the variation between the voltage pulse command and the current consumed by the motor.

  Here it can be seen that the supply voltage drops even more quickly due to the application of the enhanced safety mechanism.

6.6. In one variation, the invention is not only as a function of the motor back electromotive force coefficient Ψ, but also as a function of other parameters of the system, such as phase shift, speed, efficiency, internal resistance, inertia, gain, etc. This can be improved by obtaining the second term of the voltage of the power supply voltage pulse.

Claims (20)

Method for controlling a discontinuous screwdriver device comprising an electric motor, wherein the rotor of the electric motor is connected to a terminal unit that can be driven in rotation, said motor being powered by sequential power supply voltage pulses And determining an instantaneous power supply voltage of the motor during each of the power supply voltage pulses, the steps being at least the following steps:
A first step of measuring the instantaneous rotational frequency of the rotor in real time;
A second step of determining a voltage component of the power supply voltage pulse, wherein the component is determined by the instantaneous rotational frequency;
A third step of determining in real time the voltage of the power supply voltage pulse incorporating a voltage value in response to the instantaneous rotational frequency of the rotor.   The method of claim 1, wherein the component is selected from a predetermined set of voltage values as a function of the instantaneous rotational frequency.   The method of claim 1, wherein the component is determined as being equal to a product of the instantaneous rotational frequency with a predetermined coefficient. Each voltage of the power supply voltage pulse is:
A first term corresponding to a value obtained by multiplying a predetermined theoretical constant power supply voltage by a pulse amplitude coefficient;
The method according to any one of claims 1 to 3, corresponding to a sum of a second term corresponding to the component determined by the instantaneous rotation frequency of the rotor.   The method of claim 4, wherein the pulse amplitude factor is in the range of 0-1.   The method according to claim 4 or 5, wherein the predetermined theoretical constant power supply voltage is equal to a product of a predetermined value of current multiplied by an electric resistance of the screwdriver device.   The method according to any one of claims 4 to 6, wherein the second term is a voltage value equal to a product of the instantaneous rotational frequency of the rotor and a coefficient of a counter electromotive voltage of the motor.   8. A method according to any one of claims 4 to 7, wherein the second term considers data stored in the form of a correspondence table associating a plurality of pairs of power supply voltage values and rotational frequency values of the rotor. .   The method according to any one of claims 1 to 8, comprising detecting an operation abnormality and correcting the voltage of the power supply voltage pulse of the motor following the detection of the operation abnormality. The step of detecting an abnormal operation includes
Measuring the current consumed by the motor;
Comparing the measured value of the current consumed by the motor with a predetermined threshold;
The method of claim 9, comprising: reducing the voltage of the power supply voltage pulse of the motor when the measured value of the current consumed by the motor is greater than or equal to the threshold.   The method of claim 10, wherein the step of reducing the voltage of the power supply voltage pulse of the motor is to reduce the first term of the voltage of the power supply voltage pulse.   The step of reducing the voltage of the power supply voltage pulse of the motor is to reduce the sum of the product of the amplitude coefficient of the first term and the second term. the method of. A discontinuous screwing system comprising: an electric motor having a rotor connected to a terminal unit capable of being driven to rotate; and means for powering the motor by sequential power supply voltage pulses, wherein the power supply voltage Means for determining the instantaneous power supply voltage of the motor during each of the pulses, the means comprising at least:
Means for measuring the instantaneous rotational frequency of the rotor in real time;
Means for determining a voltage component of the power supply voltage pulse, the component being determined by the instantaneous rotational frequency;
A discontinuous screw tightening system comprising: means for obtaining the power supply voltage pulse incorporating a voltage value in real time according to the instantaneous rotation frequency of the rotor. The means for obtaining the voltage of the power supply voltage pulse in real time is:
A first term corresponding to a value obtained by multiplying a predetermined theoretical constant power supply voltage by a pulse amplitude coefficient;
14. The system of claim 13, comprising means for calculating a sum with a second term corresponding to the component determined by the instantaneous rotational frequency of the rotor.   15. The system according to claim 13 or 14, comprising means for detecting an operation abnormality and means for correcting the voltage of the power supply voltage pulse of the motor following the detection of the operation abnormality. The means for detecting an operation abnormality comprises:
Means for measuring the current consumed by the motor;
Means for comparing the measured value of the current consumed by the motor with a predetermined threshold;
The system of claim 15, comprising: means for reducing the voltage of the power supply voltage pulse of the motor when the measured value of the current consumed by the motor is greater than or equal to the threshold.   The system according to claim 14 or 16, wherein the means for reducing the voltage of the power supply voltage pulse of the motor is to reduce the first term of the power supply voltage pulse.   The means for lowering the voltage of the power supply voltage pulse of the motor is for reducing the sum of the product of the amplitude coefficient of the first term and the second term. The described system.   Computer program comprising program code instructions, wherein when the program is executed by a computer, the method according to any one of claims 1 to 12 is executed.   A computer-readable non-transitory storage medium storing the computer program according to claim 19.