• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
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  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to a method for screwing in a screw (4) with a predetermined tightening torque by means of a screwing tool (3) which is coupled to an electric motor (2), which is controlled by a controller (8). The method comprises the following method steps: - accelerating the electric motor (2) in the direction of rotation (15) to a predetermined maximum speed; - Operating the electric motor (2) in maximum speed until a drive shaft (11) of the electric motor (2) has completed a predetermined number of spindle revolutions; - Reduce the speed of the electric motor (2) to a predetermined reduced speed; Operating the electric motor (2) at a reduced rotational speed until an increase in torque exceeding a predetermined threshold value is detected by a measuring unit (14) connected downstream of the electric motor (2); - Retighten the screw (4) or nut until the predetermined tightening torque has been reached.
    公开号:AT518700A1
    申请号:T50501/2016
    申请日:2016-06-01
    公开日:2017-12-15
    发明作者:Brunner Matthias；Ing Dr Tobias Glück Dipl；Ing August Gründl Dipl；Ing Dr Andreas Kugi Dipl
    申请人:Stiwa Holding Gmbh；
    IPC主号:
    专利说明:

    The invention relates to a method for screwing a screw or nut with a predetermined tightening torque.
    Various methods for producing a screw connection between two components are known from the prior art. The methods known from the prior art relate in particular to production systems in which screws or nuts are screwed by means of a tool which is coupled to an electric motor into the respective screw or nut associated counter thread to fasten a component. The screws or nuts must be tightened with a predetermined tightening torque, wherein the tightening torque to be achieved has only a small tolerance range.
    The methods known from the prior art have the disadvantage that, in order to achieve the required tightening torque while maintaining the required tolerance range, the screwing speed must be selected to be low, in order to suppress the tightening torque falsifying dynamic effects which occur due to the inertia of the drive train.
    The object of the present invention was to overcome the disadvantages of the prior art and to provide a method which has an increased process speed while maintaining process accuracy.
    This object is achieved by a method according to claim 1.
    According to the invention a method for screwing a screw or nut with a predetermined tightening torque by means of a driving tool, which is coupled to an electric motor, is provided. The electric motor is controlled by a control. The method comprises the following method steps: producing a torque-transmitting connection between screwing tool and screw or nut; - Accelerating the electric motor in the direction of rotation to a predetermined maximum speed; - Operating the electric motor in maximum speed until a drive shaft of the electric motor has completed a predetermined number of spindle revolutions, wherein during this step, the screw or nut is screwed freely into the respective mating thread, or the mating thread is cut by means of the screw; - Reduce the speed of the electric motor to a predetermined reduced speed; Operating the electric motor at a reduced speed until, preferably by a measuring unit connected downstream of the electric motor, a torque increase is detected which exceeds a predetermined threshold value, wherein the torque increase occurs when the screw or nut comes into contact with the shoulder on the component to be fastened ; - Retighten the screw or nut until the predetermined tightening torque is reached.
    An advantage of the method according to the invention is that the method is divided into a very wide variety of method steps, with the electric motor having a different speed in the individual method steps. By this measure it is achieved that the screwing can be shortened as possible and at the same time the required tightening torque can be achieved as accurately as possible. In particular, during operation of the electric motor in a predetermined maximum speed as fast as possible screwing the screw is ensured. In this step, the screw is screwed into the corresponding mating thread, taking care that the screw is screwed freely into the thread and the shoulder is still not applied to the fastener ing component. Alternatively to the free screwing of the screw in a mating thread can also be provided that the mating thread is formed by the screw. Again, the applied torque is significantly lower than is the case when the shoulder of the screw is the case. Only in the subsequent process step in which the electric motor is operated at reduced speed is provided that the shoulder of the screw on the component to be fastened comes to rest. This concern of the shoulder of the screw on the component to be fastened results in an increase in torque. This torque increase can be detected directly, for example, by detecting the motor current in the electric motor.
    Alternatively, it is also possible for the torque increase to be detected by a measuring unit connected downstream of the electric motor, which measuring unit is designed to detect the torque, for example in the form of a torque measuring shaft.
    Furthermore, it may be expedient if, after the detection of the torque increase, the electric motor is braked to a predetermined minimum speed. The advantage here is that overbraking the screw can be prevented by braking the electric motor to minimum speed.
    Furthermore, it can be provided that the electric motor is operated at minimum speed for a predetermined or predeterminable period of time until oscillations that occur in the drive system due to the deceleration process from the reduced rotational speed to the minimum rotational speed have largely disappeared. The advantage here is that can be achieved by operating the electric motor in the minimum speed in a predetermined period of time that the drive system can swing out and thus there is no distortion of the measured torque at the measuring unit. In extreme cases, it may be necessary to select a complete standstill as the minimum speed. The oscillations that have to die out are due to the mass inertia or the inertial forces of the individual components in the drive system and due to the abrupt deceleration maneuver.
    In addition, it can be provided that, after the predetermined period of time in which the electric motor is operated at minimum speed, the further control of the electric motor is predetermined by the control on the basis of the torque measured in the measuring unit. The predetermined period of time may be reset individually for each cycle. After expiration of this predetermined time period in which the sensor signal is corrupted, it is possible to switch over to torque-torque control in order to be able to achieve the required tightening torque.
    Also advantageous is an expression according to which it can be provided that the reduced rotational speed is between 0.1% and 100%, in particular between 0.5% and 99%, preferably between 50% and 80% of the maximum rotational speed. The advantage here is that during operation of the electric motor in a reduced speed, a torque which exceeds a predetermined threshold can be detected and due to the reduced speed then sufficient time remains to further reduce the speed and adjust the required torque.
    According to a development, it is possible that directly after the detection of the torque increase, the further control of the electric motor is set by the control based on a torque value, wherein after the detection of the torque increase of the electric motor is decelerated to a predetermined minimum speed and in an initial period during the braking process the torque detected in the measuring unit is superimposed by a torque based on a model calculation and, after the initial period, the torque detected by the measuring unit serves as an input variable for the control. This alternative variant has the advantage that the process time can be further shortened and optimized. By blending the detected torque with a torque based on a minor computation, the measurement error which occurs due to the oscillation of the system after the deceleration of the electric motor can be compensated.
    Furthermore, it can be provided that directly after the detection of the torque increase, the further control of the electric motor of the control
    Based on a desired trajectory of the torque value is specified, wherein the speed profile is calculated in a feedforward control from the desired trajectory of the torque value. If a disturbance observer is used, the torque actually acting on the screw can be estimated. By fading to this estimated moment noise can be hidden.
    Furthermore, it can be provided that in a first phase after the detection of the torque increase, the torque value is estimated by means of a disturbance observer and that in a second phase after the detection of the torque increase, the torque is detected directly by the measuring unit and serves as input for the control. By presetting the torque value by means of the disturbance observer, vibrations or disturbances in the system can be filtered, so that no settling occurs in the control. After the vibrations have subsided, the torque actually measured at the measuring unit can then serve as the input value for the control.
    Furthermore, it can be provided that the transition between different rotational speeds of the individual method steps is predetermined such that no sudden increases in acceleration occur. By avoiding jump-like increases in acceleration, the jerk acting on the individual components of the screwdriver can be reduced, thereby increasing the longevity of the screwdriver.
    Furthermore, it may be expedient if in the model calculation, the inertia and / or the spring stiffness and / or the damping and the angular acceleration of the individual components installed in the drive train is taken into account. The advantage here is that based on these values or on the basis of these state variables, the dynamic behavior of the drive train can be accurately calculated and thus a distortion of the measured torque during braking or when accelerating the electric motor can be compensated.
    In addition, it can be provided that the model calculation is adjusted on the basis of the respective previous cycles in an iterative learning process, wherein used to adapt the model calculation of the time course of the measured value of the torque in the measuring unit, and the engine torque and the associated rotation angle of the drive shaft in the electric motor becomes. The advantage here is that the drive method can be adjusted and improved during operation, which on the one hand, the accuracy can be increased to achieve the tightening torque and beyond the process time can be further reduced.
    It may also be provided to extend the control loop by a feedforward control for force and / or inertia compensation, should the dynamics of the lower-level controllers not be sufficient. The pilot controls can be derived from the mathematical models. It may be sufficient to use a much simplified model, such as a pure rigid body system, which takes into account only moments of inertia and no dynamic elements. Alternatively, a dynamic system as described in this document may be used for mathematical modeling.
    Furthermore, it can be provided that a disturbance observer, in particular a Kalman filter, is used for the model calculation, which is also regulated in the first step and only superimposed on the torque detected in the measuring unit at a certain point in time. The advantage in this case is that such a disturbance observer can compare the actually applied actual values with the output variables determined from the model and as the output value an external torque can be specified to the control, whereby the accuracy in achieving the tightening torque can be improved.
    According to a particular embodiment, it is possible that between the electric motor and driving tool a transmission is arranged, by means of which the rotational speed or the torque between the electric motor and screwing tool is translated. The advantage here is that the torque of the electric motor can be translated by the transmission, with only a small engine torque is sufficient to apply sufficient torque on the screw can. In the same way is achieved by the transmission that the resolution accuracy of the engine due to the transmission ratio can be improved.
    Is spoken in this document of a screw, in addition to a screw all fasteners are addressed, which have a thread and serve to clamp a component by screwing. These are, for example, nuts, which also have a shoulder which may rest against a component to be fastened. A corresponding mating thread for a screw is a threaded hole or a nut. For screws with self-tapping threads, the associated counter-hole may be a simple hole which has no thread, as the thread is cut directly by the screw. A corresponding mating thread for a nut is a screw or a threaded pin.
    The maximum speed to which the electric motor is accelerated need not necessarily correspond to the maximum possible speed of the electric motor. Rather, it is also possible that the maximum speed results from the process parameters and is a calculated value. The predetermined maximum speed can vary from one driving process to the next.
    The threshold value of the torque which is detected may be a predetermined or individually definable absolute value of the torque, for example in Nm.
    Alternatively, it is also possible that the threshold value is not an absolute value of the torque is specified, but that as a threshold value, a predetermined or individually predefinable torque increase per rotation angle unit of the motor is specified. This threshold value of the torque increase can be defined approximately in Nm per ° rotation angle.
    In yet another embodiment, it is conceivable that a maximum change of the torque increase per rotation angle unit of the screw is specified as the threshold value. This maximum change in the torque rise per rotation angle unit can be calculated, for example, by the first derivation of the function of the torque increase per rotation angle unit of the motor. This threshold value of the change in the torque increase can be defined approximately in ΔΝιτι per Ä ° rotation angle.
    For the purposes of this document, a regulation can be understood as a two-speed degree-of-magnitude control with a subordinate engine control, wherein a control circuit with this control can also have additional pilot controls.
    Furthermore, it can be provided that a speed curve is calculated on the basis of the load characteristic and a desired desired trajectory for the external torque. This speed starts at the reduced speed and is transferred to standstill. This speed profile ensures that the external moment follows the desired setpoint trajectory sufficiently well. As a result, it is possible to compensate the remaining control deviation with a linear controller Rm. If a disturbance observer is used, the estimated signal is controlled and, at the end of the trajectory, blended to the measurement signal. If the disturbance observer is not present because the quality of the measurement signal is sufficiently good, then the measurement signal is controlled directly and thus no cross-fading is performed.
    For a better understanding of the invention, this will be explained in more detail with reference to the following figures.
    In each case, in a highly simplified, schematic representation:
    Fig. 1 is a schematic representation of a possible structure of a screwdriver;
    FIG. 2 is a flowchart of a first control strategy for screwing in a screw; FIG.
    3 is a flowchart of a second control strategy for screwing in the screw;
    4 is a structural diagram of the mechanical model of the screwdriver;
    Fig. 5 is a simplified structural diagram of the mechanical model of the screwdriver;
    6 shows an exemplary course of the external moment;
    7 is a structural diagram of a control circuit for the torque control;
    8 shows an exemplary controlled system of a torque control;
    9 is a structural diagram of a control circuit with disturbance observer and load precontrol, torque precontrol and inertia compensation;
    10 is a structural diagram of a control loop with Störgrößenbeobachter and torque precontrol and inertia compensation.
    11 is a structural diagram of a control loop with disturbance observer and torque precontrol;
    FIG. 12 is a structural diagram of a control circuit with disturbance observer and load precontrol as well as torque precontrol; FIG.
    13 is a structural diagram of a control circuit with load precontrol, torque precontrol and inertia compensation;
    14 is a structural diagram of a control circuit with torque precontrol and inertia compensation;
    15 is a structural diagram of a control loop with torque precontrol;
    16 is a structural diagram of a control circuit with load pre-control and
    Torque feedforward control.
    By way of introduction, it should be noted that in the differently described embodiments, the same parts are provided with the same reference numerals or the same component names, the disclosures contained in the entire description can be mutatis mutandis to the same parts with the same reference numerals or component names. Also, the location information chosen in the description, such as top, bottom, side, etc. related to the immediately described and illustrated figure and these position information in a change in position mutatis mutandis to transfer to the new location.
    1 shows a schematic representation of a process screwdriver 1. The process screwdriver 1 comprises an electric motor 2, and a screwing-in tool 3 coupled to the electric motor 2. The screwing-in tool 3 can be coupled with a screw 4 or a nut in order to provide a torque-transmitting connection between the screwing tool 3, and the screw 4 can produce. Thereby, the screw 4 can be automatically screwed into a corresponding mating thread 5 of a receiving object 6 in order to fix a component 7 on the receiving object 6 can.
    The screwing tool 3 or the screw 4 may have a variety of forms for power transmission, such as hexagon, hexagon socket, torx, etc.
    Furthermore, it can be provided that the electric motor 2 is designed as a servomotor. Such a servomotor may be, for example, a synchronous motor. In addition, it can be provided that the electric motor 2 is connected to a controller 8. Furthermore, it can be provided that a frequency converter is formed, which cooperates with the electric motor 2 and predetermines the rotational speed of the electric motor 2.
    As can further be seen from FIG. 1, provision can be made for a transmission 9 to be coupled to the electric motor 2. By means of the gear 9, the drive torque or the rotational speed of the electric motor 2 can be translated. In particular, it will be expedient if the transmission 9 is configured in such a way that a higher rotational speed is applied to the transmission input 10, which is coupled to a drive shaft 11 of the electric motor 2, than to a transmission output shaft 12 which adjoins a transmission output 13 of the transmission 9 located.
    Furthermore, it is provided that a measuring unit 14 is arranged between the electric motor 2 and driving tool 3, which is designed to detect the convincing tool 3 applied torque. The measuring unit 14 is coupled to the controller 8. The measuring unit 14 is preferably arranged as close as possible to the screwing tool 3. If the process screwdriver 1 comprises, for example, a transmission 9, then it is expedient that the measuring unit 14 is arranged in any case between the transmission 9 and screwing tool 3, wherein the measuring unit 14 should, of course, be arranged as close as possible to the screwing tool 3. In other words, it is advantageous if the measuring unit 14 is arranged on the transmission output side 13 of the transmission 9.
    The transmission output shaft 12 is coupled with respect to rotational speed and torque directly to the screwing tool 3, whereby for screwing the screw 4 into the mating thread 5, the transmission output shaft 12 must move in the direction of rotation 15. The Zudrehrichtung 15 is dependent on the thread orientation of the screw 4. If the screw 4 has, for example, a right-hand thread, then the direction of rotation 15 is also clockwise. However, if the screw 4 has a left-hand thread, then the direction of rotation 15 is also left-handed.
    Furthermore, it can be provided that a coupling 16 is provided for connecting the electric motor 2 and the transmission 9 or for connecting the transmission 9 and the measuring unit 14 or for connecting the measuring unit 14 and screwing tool 3. The coupling 16 is used in particular for torque transmission between the individual components and is therefore preferably arranged between the individual components. In particular, it can be provided that the screwing tool 3 is coupled to the drive train. Therefore, various screwing tools 3 can be used for different screws 4 on the same process screwdriver 1.
    Furthermore, it can be provided that a bearing 17 is formed, which serves to absorb the forces occurring.
    The general mode of operation of the process wrench 1 will now be explained with reference to FIG.
    The screwing tool 3 is brought into engagement with the screw 4 and the screw 4 is subsequently screwed into the mating thread 5. In a first screw-in while the screw 4 is easily screwed into the mating thread 5. At the end of this screwing in a shoulder 18 of the screw 4 comes into contact with the component 7, whereby the torque for screwing the screw increases abruptly. Subsequently, the component 7 is pressed by the screw 4 to the receiving object 6, wherein the torque is further increased until a predetermined tightening torque is reached.
    It can be said that the screwing of the screw 4 is divided into two stages. The first stage is a screwing in which the screw 4 is screwed freely into the mating thread 5 and the shoulder 18 of the screw 4 is not applied to the component 7.
    The second stage is an Anziehstufe in which the shoulder 18 of the screw 4 rests on the component 7 and therefore an increased torque on the screw 4 must be applied.
    In the screwing can be provided that the electric motor 2 is superimposed speed controlled until an external threshold is exceeded. In the Anziehstufe can be provided that the electric motor 2 is superimposed torque-controlled.
    In the tightening stage, a pre-defined tightening torque can be adjusted by means of a kasked two-degree of freedom control. This cascaded control consists of an internal speed control, a superimposed torque control and a corresponding model-based feedforward control.
    With the aid of the model-based precontrol, a rotational speed is predetermined so that the course of the external torque actually acting on the screw 4 can follow the predetermined desired trajectory with sufficient accuracy. This two-degree-of-freedom control can also be extended by further model-based feedforward controls, with which a load and / or inertia compensation is achieved. If the mechanical coupling between the drive and the tool holder is sufficiently rigid, then the torque detected at the measuring unit 14 can be used as a direct feedback variable for the torque control. If this is not the case, then the torque detected at the measuring unit 14 in acceleration phases includes inertial forces due to the inertia of the screwing tool.
    In order to take this circumstance into account, different sequence or control strategies are proposed, which will be described in more detail below.
    For example, can be provided in a first strategy that after the occurrence of the torque increase due to the stop of the shoulder 18 on the component 7, the electric motor is decelerated to a minimum speed and this is kept constant until the torque detected by the measuring unit 14 again has settled on the torque value actually applied to the screwing tool 3. Starting from this minimum speed, only negligible deviations occur between the torque detected at the measuring unit 14 and the torque value actually applied to the screwing tool 3, so that regulation of the electric motor 2 to the tightening torque is possible.
    In a second strategy, it may be provided that the torque value actually applied to the screwing-in tool 3 is estimated with a disturbance observer and the control takes place in accordance with the estimated value. This disturbance observer is based on a mathematical model of the process screwdriver 1 as a simulation. Model uncertainties and external disturbances can be compensated by means of an output feedback. The disturbance observer uses the setpoint motor torque, the measured motor rotation angle and the torque detected at the measuring unit 14 to reconstruct the torque actually applied to the screwing tool 3. This estimated load force can then be used as a feedback variable for the torque control of the electric motor 2.
    The difficulty with the control is to keep the process speed high and the moments occurring within preset limits. If an ideal, interference-free route is assumed, an engine speed curve can be found which makes it possible to set a desired tightening torque. In the real application, however, the initial position of the screws 4 is only roughly known in addition to the interference and the measurement noise and this varies between different screws 4 by up to two full turns.
    In order to achieve a defined tightening torque while keeping the process speed as high as possible, the control strategies according to the invention have been developed.
    As long as the screw rotates freely, no significant increase in the torque actually applied to the screwing tool 3 is to be expected. It therefore makes sense to directly specify a motor speed profile without additional torque control in this screwing phase. Only when the shoulder 18 rests on the component 7, there is a rapid increase in the torque applied to the screwing 3 and the torque control is active. In the tightening step, a motor speed profile is specified in which different speed levels are continuously connected to each other. This ensures that the mechanical components of the process wrench 1 are not unnecessarily strained and the excitation of vibrations in the system is kept low.
    The aim of the regulation is to regulate the actual torque applied to the insertion tool so that it reaches a defined value, also referred to as tightening torque.
    The torque actually applied to the screwing tool 3 is to be measured by means of the measuring unit 14 and to serve as a feedback variable in the control. However, it should be mentioned that the torque measured in the measuring unit 14 only corresponds to the torque actually applied to the screwing tool 3 when the screwing tool 3 is not being accelerated or decelerated and therefore no dynamic effects due to the inertia of the individual components occur. In other words, the torque actually applied to the screwing tool 3 can be accurately measured by the measuring unit 14 when the screwing tool 3 is stationary or moving at a constant rotational speed, this condition also having to last for a certain period of time, so that vibrations have already subsided.
    2 shows a flow chart of a schematic sequence of the first control strategy for screwing in the screw 4.
    At the decision paths there is a plus (+) for condition is met. A minus (-) stands for condition is not met.
    In method step 1, the drive shaft 11 of the electric motor 2 is accelerated to maximum speed. In order to accelerate the electric motor 2 to maximum speed, a specific time profile of the angular velocity or a certain acceleration ramp can be predetermined on the basis of which the electric motor 2 is accelerated. In the query A is queried whether the drive shaft 11 of the electric motor 2 has already completed a predetermined number of spindle revolutions. The electric motor 2 is operated at maximum speed until reaching the predetermined number of spindle revolutions in the query A to fulfill the condition. The number of spindle revolutions which serves as a trigger for switching to method step 2 is selected as high as possible, but chosen so low that it is possible in all conceivable cases due to the tolerances that the shoulder 18 of the screw 4 is not during this process step on the component 7 comes to the concern. During method step 1, it may be provided that the torque measured at measuring unit 14 is not interrogated or at least not included in the engine control.
    Subsequently, in method step 2, the electric motor 2 is operated at reduced speed. The reduced speed serves to ensure that sufficient time remains in the detection of a torque increase in the measuring unit 14 in order to reduce the engine speed or to change over to a torque control. The rotational speed in the reduced speed is dependent on how fast the electric motor 2 can be braked and what angle of rotation the screw 4 can still be rotated after placing the screw 4 on the component 7. For example, if this rotation angle is very large, the reduced speed may be high and approximately equal to the maximum speed.
    The transition from maximum speed to reduced speed can also be carried out according to a predetermined time profile of the angular velocity. During operation of the electric motor 2 at a reduced speed, the measuring unit 14 is activated in order to be able to detect when the shoulder 18 of the screw 4 comes into contact with the component 7, as a result of which a sudden increase in the torque detected in the measuring unit 14 occurs. In the query B it is determined whether the torque detected in the measuring unit 14 or its gradient or gradient curve has reached a certain predefined threshold value and when the threshold value is reached, the method step 3 is initiated.
    In method step 3, the electric motor 2 is operated at a minimum speed. The minimum speed may vary from process to process and is dictated by the current process parameters. In extreme cases, it may even be necessary for the minimum speed to be zero or approximately zero. The braking of reduced speed to minimum speed should go as quickly as possible or abruptly within the framework of the strength values of the process screwdriver 1. In method step 3, the electric motor 2 is operated at minimum speed until the vibrations occurring in the drive train due to the abrupt deceleration maneuver have faded out. For this purpose, a precalculated time duration for the decay of the oscillations is interrogated in query C.
    In an alternative variant, it can also be provided that the time required for the decay of the oscillations is not calculated on the basis of a model, but that it is adapted in an iterative method or that the
    Decay of the vibrations is detected by detecting the engine torque in the electric motor 2 in comparison with the measured torque in the measuring unit 14.
    If the waiting time is reached, the torque control is subsequently activated in method step 4 and the screw 4 is tightened while observing the torque measured in the measuring unit 14.
    According to the query D, the screw is tightened until a predetermined tightening torque is reached. After reaching this tightening torque of the current screwing is completed according to the method step 5.
    3 shows a flow chart of a schematic sequence of a second control strategy for screwing in the screw 4, the method steps 1 to 5 including the query B being the same as already described in FIG. 2. For the sake of brevity, the description of FIG. 3 therefore begins with method step 3, which differs from method step 3 of FIG. 2.
    In method step 3, a Trajketorienfolgeregelung is activated by means of two-degree of freedom controller and the speed of the electric motor 2 predetermined by this. The desired trajectory is compared in the control with the output of the disturbance observer. The virtually predetermined torque, also called desired trajectory, is calculated on the basis of a model of the screw 4. In the model consideration, each torque angle of the screw is assigned an applied torque. Query C queries whether an end of the time period in which the target trajectory is to be used is reached. If this is the case, then in step 4, the torque measured in the measuring unit 14 is used as a feedback variable for the control and the screw 4 is tightened to the tightening torque.
    FIG. 4 shows a mechanical model of the screwdriver 4 with the gear 9, which serves as the basis for the mathematical modeling of the screwdriver 4. For the modeling, the moments of inertia are recorded according to the data sheets of the components and the transitions between the individual components are considered as spring-damper combinations. The values for the spring constants also follow from the data sheets of the components used, while the damping constants are determined empirically. The input variable of the model forms the engine torque Mm, which counteracts the friction torque Mrm of the drive. The transmission is assumed to be lossless and modeled as a linear spring mass damper element. The moment of inertia of the gear 0g is considered together with the engine inertia 0m on the drive side. The drive-side engine torque Mm acts via which the transmission 9 is amplified by the gear factor ig, while the engine angular position cpm on the output side is reduced by a factor of 1 / ig. The compliance of the transmission 9 is modeled on the basis of a linear spring with the spring constant cg and a linear damper with the damper constant dg. The angle or the moment between the transmission 9 and the first clutch 16 are denoted by cpg and Mg, respectively.
    The moments of inertia 0k of the clutches 16 are taken into account on the input side and the output side, respectively, and are coupled to one another via a linear element with the spring constant Ck and the damper constant dk. The output-side geared torque Mg acts on the first clutch 16. The torque on the clutch output side is designated Mk and the associated rotational angle with q> k. Analogously to the clutches, the measuring unit 14 with the inertia moment 0si of the drive side and 0S2 of the driven side and the spring-damper element with the spring constant cs and the damper constant ds are integrated into the drive train. The new angular position and the virtual moment are denoted by cps and Ms, and are applied to the driving side of the second clutch 16. This coupling 16 connects the torque sensor with the shaft on which the screwing tool is mounted. The shaft has the moment of inertia 0W, and the rotation angle cpw and the moment Mw are the quantities directly applied to the screw 4. At this moment, the frictional losses Mrw caused by the bearing of the shaft counteract the external moment of the screw 4 Mext. The moment of inertia of the screw 4 is negligible due to the small dimensions relative to the shaft and tool.
    Fig. 5 shows a simplified model, wherein it is assumed for the simplified structure that the spring constants of the transmission, the clutches and the sensor construed as a series circuit and thus in the Ersatzfederkonstante
    can be transferred. The sensor has the lowest with cs
    Rigidity in this series circuit and thus determines the size of the Ersatzfederkonstante significantly. The equivalent friction ds, r is determined empirically.
    All moment of inertia of the sensor drive side are transformed taking into account the translation on the drive side of the transmission and in the moment of inertia
    summarized. The moment of inertia of the sensor output side is determined by θ2 = 0s2 + ^ k + 6w. Like the detailed model, the engine torque and the external moment are called Mm and Mext. The moments Mrm, r and M ™, r indicate the moments resulting from the frictional losses of the drive and the bearing.
    6 shows an exemplary profile of the external moment over the course of the shaft angle cpw. The exemplary course of the external moment can be determined by a trial. This exemplary course is also referred to as a load model.
    In order to enable a wide range of screw applications and to ensure the simplicity of the model adaptation, the load model of the specific application cases is determined empirically. The aim is to metrologically record a characteristic which indicates the relationship between the external moment Mext and the screw-in angle cpw. For this purpose, a screw 4 with constant speed, according to the application, so far screwed until a maximum torque limit is reached on the electric motor 2. Due to the constant speed, the measuring signal on the measuring unit 14 coincides with the externally acting moment. The angular position of the shaft can not be detected metrologically. For this reason, the transfer function from the motor angle (pm to the shaft angle q> w is calculated from the nutrunner model and analyzed in the frequency domain.) It has been shown that the transfer function in the relevant frequency range is essentially determined only by the transmission factor ig and thus the assumption In this situation, the relationship between the external moment Mext and the shaft angle <pw can be detected, and a characteristic determined in this way is shown as an example in FIG.
    The course of the characteristic curve corresponds to that of a nonlinear spring Mext = k (q> w) * q> w with the angle-dependent stiffness k ((pw).) For the design of the screwing strategies described in FIGS If ttrigger denotes the time at which this exceeding is valid, then a time transformation is defined with Wis = t-trigger, and in the application stage, the torque increase is as first approximation as shown in FIG constant.
    FIG. 7 shows a structural diagram of a possible torque controller Rm for torque control. The torque controller Rm becomes active as soon as the shoulder 18 of the screw 4 rests on the component 7 and the application stage begins. Due to the assumption of an ideal motor-torque control loop, the replacement model of the controlled system for the superimposed torque controller can be simplified.
    This replacement model is composed of the motor speed controller and the model of the process screwdriver 1 and is shown in Fig. 8 in detail. The nutrunner model is divided into two separate transfer functions. The transfer function Gü) m (s) with Mm as input and u) m as output forms the output feedback for the motor speed controller Rui (s), while the transfer function Gms (s) from the input Mm to the output Ms the measuring unit 14 maps. The transfer function of the entire controlled system G ^ m ^ s) from the input to the output Ms thus consists of the closed motor speed control loop
    and the sensor transfer function
    Gms (s) together and can be to Gw ^, ms (s) =
    1 determine.
    In the figures 9 to 15 different structural diagrams of possible control circuits for torque control are shown, all figures build on the figure 7 on. In order to avoid unnecessary repetition, reference is made to FIG. 7 or the respective preceding figures.
    In the exemplary embodiment according to FIG. 9, the input variable for the torque controller Rm is not the sensor signal Ms, as is the case in FIG. 7, but instead an estimated torque Mext is provided as input to the torque controller Rm by a disturbance observer 19. Furthermore, a torque pre-control Vm, a load pre-control Vext and an inertia compensation νω are provided.
    In the embodiment according to FIG. 10, an input torque for the torque controller Rm is fäext estimated by the disturbance observer 19. Furthermore, a torque precontrol Vm and an inertia compensation νω are provided.
    In the embodiment according to FIG. 11, an input torque for the torque controller Rm is fäext estimated by the disturbance observer 19. Furthermore, a torque precontrol Vm is provided.
    In the exemplary embodiment according to FIG. 12, an input torque for the torque controller RM is a torque Mext estimated by the disturbance observer 19. Furthermore, a torque precontrol Vm and a load precontrol Vext are provided.
    In the exemplary embodiment according to FIG. 13, the sensor signal Ms serves as an input variable for the torque controller Rm. Furthermore, a torque precontrol Vm, a load precontrol Vext and an inertia compensation νω are provided.
    In the embodiment according to FIG. 14, the sensor signal Ms serves as an input variable for the torque controller Rm. Furthermore, a torque precontrol Vm and an inertia compensation Vm are provided.
    In the exemplary embodiment according to FIG. 15, the sensor signal Ms serves as an input variable for the torque controller Rm. Furthermore, a torque precontrol Vm is provided.
    In the embodiment according to FIG. 16, the input variable for the torque controller is Rivida's sensor signal Ms. Furthermore, a torque precontrol Vm and a load precontrol Vext are provided.
    The embodiments show possible embodiments, it being noted at this point that the invention is not limited to the specifically illustrated embodiments thereof, but also various combinations of the individual embodiments are mutually possible and this variation possibility due to the teaching of technical action by representational invention in Can the expert working in this technical field.
    The scope of protection is determined by the claims. However, the description and drawings are to be considered to interpret the claims. Individual features or combinations of features from the illustrated and described different embodiments may represent for themselves inventive solutions. The task underlying the independent inventive solutions can be taken from the description. All statements of value ranges in the present description should be understood to include any and all sub-ranges thereof, e.g. is the statement 1 to 10 to be understood that all sub-areas, starting from the lower limit 1 and the upper limit 10 are included, ie. all sub-areas begin with a lower limit of 1 or greater and end at an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.
    For the sake of order, it should finally be pointed out that for a better understanding of the construction, elements have been shown partially unevenly and / or enlarged and / or reduced in size.
    REFERENCE SIGNS LIST 1 Process screwdriver 2 Electric motor 3 Screw-in tool 4 Screw 5 Counter thread 6 Pick-up object 7 Component 8 Control 9 Gearbox 10 Gearbox input 11 Drive shaft 12 Transmission output shaft 13 Transmission output 14 Measuring unit 15 Direction of rotation 16 Coupling 17 Bearing 18 Shoulder 19 Disturbance monitor
    权利要求:
    Claims (16)
    [1]
    claims
    1. A method for screwing a screw (4) or nut with a predetermined tightening torque by means of a driving tool (3) which is coupled to an electric motor (2), which is controlled by a controller (8), characterized in that the method follows Method steps include: - Producing a torque-transmitting connection between screwing tool (3) and screw (4) or nut; - accelerating the electric motor (2) in the direction of rotation (15) to a predetermined maximum speed; - Operating the electric motor (2) in maximum speed until a drive shaft (11) of the electric motor (2) has completed a predetermined number of spindle revolutions, wherein during this step, the screw (4) or nut is screwed freely into the respective mating thread (5), or the counter thread (5) is cut by means of the screw (4); - Reduce the speed of the electric motor (2) to a predetermined reduced speed; - Operating the electric motor (2) in a reduced speed until a torque increase is detected, which exceeds a predetermined threshold, wherein the torque increase occurs when the screw (4) or nut with the shoulder (18) on the component to be fastened (7 ) comes to the concern; - Retighten the screw (4) or nut until the predetermined tightening torque is reached.
    [2]
    2. The method according to claim 1, characterized in that the torque increase of a the electric motor (2) downstream measuring unit (14) is detected.
    [3]
    3. The method according to claim 1 or 2, characterized in that after the detection of the torque increase, the electric motor (2) is braked to a predetermined minimum speed.
    [4]
    4. The method according to claim 3, characterized in that the electric motor (2) is operated for a predetermined or predeterminable period of time at minimum speed until vibrations which occur in the drive system due to the braking process from the reduced speed to the minimum speed, have largely eluded.
    [5]
    5. The method according to claim 4, characterized in that after the expiration of the predetermined period in which the electric motor (2) is operated at minimum speed, the further control of the electric motor (2) of the control (8) on the basis of in the measuring unit (14 ) measured torque is specified.
    [6]
    6. The method according to any one of the preceding claims, characterized in that the reduced speed is between 0.1% and 100%, in particular between 0.5% and 99%, preferably between 50% and 80% of the maximum speed.
    [7]
    7. The method according to any one of the preceding claims, characterized in that directly after the detection of the torque increase, the further control of the electric motor (2) is predetermined by the control (8) on the basis of a torque value, wherein after the detection of the torque increase of the electric motor (2 ) is decelerated to a predetermined minimum speed and in an initial period during the deceleration process the torque detected in the measuring unit (14) is superimposed by a theoretical calculation based on a desired trajectory torque and after the initial period, the torque detected by the measuring unit (14) as input to the control (8) is used.
    [8]
    8. The method according to any one of the preceding claims, characterized in that directly after the detection of the torque increase, the further control of the electric motor (2) is predetermined by the control (8) based on a desired trajectory of the torque value, the Drehzahlver running in a feedforward the desired trajectory of the torque value is calculated.
    [9]
    9. The method according to claim 8, characterized in that in a first phase after the detection of the torque increase, the torque value is estimated by means of a Störgrößenbeobachter (19) and that in a second phase after the detection of the torque increase, the torque directly from the measuring unit (14) is detected and serves as input to the control (8).
    [10]
    10. The method according to any one of the preceding claims, characterized in that the transition between different speeds of the individual process steps is specified such that no sudden increases in acceleration occur.
    [11]
    11. The method according to claim 7, characterized in that in the model calculation of the process screwdriver 1, the inertia and / or the spring stiffness and / or the damping and the angular acceleration of the individual components installed in the drive train (7) is taken into account.
    [12]
    12. The method according to claim 7 or 11, characterized in that the model calculation is adjusted based on the respective preceding cycles in an iterative learning process, wherein for adapting the model calculation of the time course of the measured value of the torque in the measuring unit (14), and the engine torque and the associated angle of rotation of the drive shaft (11) in the electric motor (2) is used.
    [13]
    13. The method according to any one of claims 7 to 8, characterized in that a Störgrößenbeobachter (19), in particular a Kalman filter, is used for the cross-fading of model calculation and in the measuring unit (14) detected torque.
    [14]
    14. A method according to claim 13, characterized in that a cross-fading is carried out between the torque estimated in the disturbance variable observer (19) and actually acting on the screw (4) and the torque detected in the measuring unit (14).
    [15]
    15. The method according to any one of the preceding claims, characterized in that between the electric motor (2) and screwing tool (3) a transmission (9) is arranged, by means of which the speed or the torque between the electric motor (2) and screwing tool (3) translated becomes.
    [16]
    16. The method according to any one of the preceding claims, characterized in that the trajectory planning is based on a load model, which is determined empirically.
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    同族专利:
    公开号 | 公开日
    EP3463756A1|2019-04-10|
    CN109476001B|2021-02-09|
    US20200324397A1|2020-10-15|
    EP3463756B1|2020-03-25|
    WO2017205887A1|2017-12-07|
    AT518700B1|2020-02-15|
    CN109476001A|2019-03-15|
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    ATA50501/2016A|AT518700B1|2016-06-01|2016-06-01|Method for screwing in a screw with a predetermined tightening torque|ATA50501/2016A| AT518700B1|2016-06-01|2016-06-01|Method for screwing in a screw with a predetermined tightening torque|
    EP17739845.0A| EP3463756B1|2016-06-01|2017-05-31|Method for screwing in a screw to a predetermined tightening torque|
    CN201780033743.0A| CN109476001B|2016-06-01|2017-05-31|Method for screwing in a screw with a predetermined tightening torque|
    PCT/AT2017/060142| WO2017205887A1|2016-06-01|2017-05-31|Method for screwing in a screw to a predetermined tightening torque|
    US16/305,557| US20200324397A1|2016-06-01|2017-05-31|Method for screwing in a screw to a predetermined tightening torque|
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