Method for controlling an electric tool

Abstract

The invention relates to a method for controlling an electric tool, in particular an electrohydraulic expansion device, implemented in the electric tool, the method comprising the steps: starting an electric motor of the electric tool; measuring a current i of the electric motor; when a specified limit current value di is exceeded, turning off the electric motor for a specified holding period Δt; after the specified holding period Δt has elapsed, starting the electric motor until the end of the movement; turning off the electric motor at the end of the movement.

Description

[0001]Novopress… Method for controlling a power tool The present invention relates to a method for controlling a power tool, in particular an electro-hydraulic expansion device. Furthermore, the present invention relates to such an expansion device, a method for pipe connecting, and such a pipe connection. Figures 1A - 1D schematically show the steps for axial pipe connection, in particular of plastic pipes. In the first step, shown in Fig. 1A, a sleeve or collar 12 is pushed over a pipe 10. Subsequently, shown in Fig. 1B, the end of the pipe 10 is expanded to obtain an expanded pipe end section 11. Subsequently, according to Fig. 1C, a pipe fitting 14 is pushed into the expanded pipe end section 11. In a final step, shown in Fig.1D, the sleeve or collar 12 is pushed towards the pipe end towards the pipe fitting 14 to ensure a secure connection between the pipe 10 and the pipe fitting 14. The sleeve 12 can be pushed onto the expanded pipe end section 11, for example, using a suitable pushing device or assembly pliers. It has been shown that during the process of expanding pipes, particularly plastic pipes, the pipes have pronounced elastic properties and thus the timing of the expansion process has a significant influence on the quality of the connection. In particular, elastic recovery of the expanded pipes can prevent a secure connection between the pipe and the pipe fitting if the pipe fitting is only inserted into the expanded pipe end section 11 after the elastic recovery.This can result in the fitting not being inserted sufficiently deep into the pipe, meaning that the required friction surface size is not achieved. The object of the present invention is to provide a method for controlling a power tool, and in particular an electro-hydraulic expansion device, with which an improvement in the connection can be achieved. This object is achieved by the method according to claim 1 and the method according to claim 16. Furthermore, the object is achieved by an expansion device according to claim 13 and a pipe connection according to claim 15.The method according to the invention for controlling a power tool and in particular an electro-hydraulic expander is implemented in the power tool and comprises the following steps: a) starting an electric motor of the power tool; b) detecting a current ^ of the electric motor; c) if a predetermined current limit value ^^ is exceeded, switching off the electric motor for a predetermined holding time Δ^; d) after the predetermined holding time Δ^ has elapsed, starting the electric motor until the end of the travel; e) switching off the electric motor when the end of the travel is reached. If the power tool is an expander, it can have an expander head that is connected to a pipe end. The expander head can have an enlargeable diameter, whereby the pipe end is expanded. The power tool is driven by an electric motor.If the power tool is designed as an electro-hydraulic expander, it has a hydraulic force conversion device that converts the movement of the electric motor into a hydraulically driven expanding movement of the expander head. The current ^ of the electric motor is measured, and if a predefined current limit ^^ is exceeded, the electric motor is switched off for a predefined holding time Δ^. After the predefined holding time Δ^ has elapsed, the electric motor is then switched back on until the end of the travel. Upon reaching the end of the travel, the electric motor is switched off, and the work process or the expanding process is completed.Due to the specified holding time Δ^, the elastic shrinkage effect of the pipe is counteracted, so that the onset of elastic recovery is delayed and a connection with another pipe or pipe fitting can be created before elastic recovery occurs. This improves the quality of the resulting connections. The current ^ of the electric motor is used to determine the point in time at which the expansion process is interrupted for the specified holding time Δ^. The preferred length is an expected holding time ^. Halt determined, whereby in particular the current ^ of the electric motor is recorded upon reaching the expected holding time ^ Halt . This makes it unnecessary to constantly measure the electric motor current throughout the entire travel of the power tool. Instead, the current is only measured after the expected holding time has been reached. Haltthe current ^ of the electric motor is detected. This reduces the effort required to detect the current ^ of the electric motor, since in particular the specified limit value ^^ is exceeded and the electric motor is only switched off for the specified holding time Δ^ after the expected holding time ^ has been reached. Halt Preferably, once the expected holding time ^ Halt The motor speed or current of the electric motor is reduced. This can be done, for example, by adjusting the pulse width modulation. This allows the motor to continue to run until the expected holding time ^ is reached. Halt A high motor speed must be selected to achieve a sufficiently fast working process or expansion process. Upon reaching and after the expected holding time ^ HaltThe expansion process then takes place at a reduced motor speed so that an exceedance of the specified current limit ^^ can be detected in good time, which is then used to switch off the electric motor for the specified holding time Δ^. Preferably, before the expected holding time ^ is reached Halt an average current ^̃ is detected, whereby the current limit ^^ depends on the average current ^̃. The average current ^̃ can be the current ^ of the electric motor averaged over a given time interval. In particular, immediately before reaching the expected holding time ^ Halt the average current ^̃ is recorded. Thus, the average current ^̃ can be measured less than 3 seconds before the expected holding time ^ Halt , preferably less than 2 seconds before the expected holding time ^ Halt and most preferably less than 1 second before the expected hold time ^ HaltPreferably, the current limit ^^ is 0.5 – 1 times the average current ^̃ and preferably 0.6 – 0.8 times the average current ^̃. This is especially true if, after reaching the expected holding time ^ Halt the motor speed or the current of the electric motor is reduced to slow down the journey. If this does not happen, the current limit ^^ can be, in particular, 1 – 5 times the average current ^̃ and preferably 1 – 2 times the average current ^̃. Preferably, the expected holding time ^ Halt determined depending on an average voltage ^ ^and a temperature ^, wherein the temperature ^ is in particular the ambient temperature and / or an operating temperature of the power tool, such as the oil temperature in an electro-hydraulic expander. In particular, if the power tool is a battery-operated power tool, the average voltage ^ ^ The influence of the battery's charge level is taken into account. At the same time, the influence of temperature on the expansion process is taken into account. The average voltage ^ ^ and / or the temperature ^ is recorded, in particular immediately after starting the electric motor (step a) to determine the expected holding time ^ Halt . Preferably, the average voltage ^ ^ and / or the temperature ^ after the starting current of the electric motor has dropped. Alternatively, the average voltage ^ ^and / or the temperature ^ is detected within the first 0-5 seconds, preferably within the first 0-3 seconds, and particularly preferably within the first 0-1 second after the start of the electric motor. Preferably, the expected holding time ^ Halt immediately after recording the mean voltage ^ ^ and / or temperature ^. Preferably, the expected holding time ^ Halt determined by a polynomial ^ Halt ^^ ^ ^, where the polynomial is in particular of degree 2, degree 3 or higher. Preferably, the expected holding time ^ Halt determined by Here, ^, ^, ^, and ^ are the coefficients of the monomials of the polynomial and can be determined, for example, by fitting the polynomial curve to a large number of measured expansion runs. Preferably, the coefficients are dependent on the temperature ^ linearly, quadratically, or with a higher power. This takes the temperature into account by adjusting the polynomial coefficients, thus allowing for a temperature-dependent correction of the expected holding time ^. Halt Preferably, the coefficients of the polynomial are ^=^(^)=^ ^ ^ 2 +^ ^ ^+^ ^ ^=^(^)=^ ^ ^ 2 +^ ^ ^+^ ^ ^=^(^)=^^^ 2 +^^^+^^ ^=^(^)=^ ^ ^ 2 +^ ^ ^+^ ^ In the example of a third degree polynomial to determine the expected holding time ^ Halt ^^ ^ ^ results from this This results in the coefficients ^ i , ^ i, ^ i with ^ = {^, ^, ^, ^} corresponding to the above-mentioned fitting of the polynomial to a large number of expansion runs at different temperatures ^. In particular, the coefficients are: ^ ^ : between 10 -6 and 10 -5 , especially between 6*10 -6 and 7*10 -6 ; ^ ^ : between -10 -4 and -10 -3 , especially between -10 -4 and -2*10 -4 ; ^ ^ : between -10 -2 and -10 -1 , especially between -2*10 -2 and -4*10 -2 ; ^ ^ : between -10 -4 and -10 -3 , especially between -10 -4 and -2*10 -4 ; ^ ^ : between 10 -3 and 10 -2 , especially between 2*10 -3 and 4*10 -3 ; ^ ^ : between 1 and 5, especially between 1 and 2; ^ ^ : between 10 -3 and 10 -2 , especially between 10 -3and 2*10 -3 ; ^ ^ : between -10 -2 and -10 -1 , especially between -10 -2 and -2*10 -2 ; ^ ^ : between -10 and -20, especially between -12 and -14; ^ ^ : between -10 -3 and -10 -2 , especially between -10 -3 and -2*10 -3 ; ^ ^ : between -10 -4 and -10 -3 , especially between -2*10 -4 and -3*10 -4 ; ^ ^: between 10 and 100, especially between 40 and 60. To determine the polynomial, a predetermined number of trips are carried out at different constant temperatures, preferably three different temperatures, and different battery charge levels covering the entire voltage spectrum. From these values, a polynomial, particularly of the third degree, is derived for each temperature using fitting. For each resulting monomial (A, B, C, D), the corresponding coefficients for a quadratic dependency can then be calculated using the given temperatures. Preferably, the expected holding time ^ Haltadjusted using a device-specific correction value ^, whereby the device-specific correction value ^ is determined by means of a calibration run. The calibration run can be carried out once, for example before delivery of the expander, or recurringly at intervals which coincide, for example, with the maintenance intervals of the expander. The device-specific correction value ^ takes into account the wear of the electric motor as well as manufacturing tolerances of the electric motor. The calibration run is preferably carried out without tools and in particular without an expander head. The correction value ^ preferably depends linearly, quadratically or with a higher power on the temperature ^.Since a constant correction value ^ may not be sufficient under the various temperature conditions under which an expansion run takes place, this is determined depending on the temperature in order to achieve greater accuracy in determining the expected holding time ^. Halt to achieve. Preferably, this results in the determination of the expected holding time ^ Halt using a polynomial ^ Halt ^^ ^ ^ 3rd degree to …×[1+^(^1^ 2 +^2^+^3)] The correction value ^ is preferably . Where ^^^ is the actual temporal position of the force increase during the calibration run and ^^^^ is the average voltage ^ ^and the temperature ^ dependent expected holding time of the calibration run and can be determined analogously to that described above. ^1, ^2 and ^3 are coefficients which are obtained, for example, by fitting the correction value to a large number of expansion runs at different temperatures ^. In particular, ^1 : between -10 -5 and -10 -4 , especially between -5*10 -5 and -6*10 -5 ; ^2 : between 10 -3 and 10 -2 , especially between 5*10 -3 and 6*10 -3; ^3 : between 0.01 and 0.2, in particular between 0.1 and 0.12. The predetermined holding time Δ^ is preferably between 1 second and 5 seconds and in particular between 1 second and 2 seconds. The interruption of the travel for the predetermined holding time preferably takes place for less than 2s, preferably less than 1s and particularly preferably less than 0.6s, i.e. essentially immediately before the end of the travel. Preferably, when the end of the travel is reached, a hydraulic valve is opened and the electric motor is switched off. In particular, the electric motor is switched off due to an increase in speed of the electric motor when the hydraulic valve is opened. Furthermore, the present invention relates to an expanding device with an expanding head for expanding pipe ends with an electric motor for actuating the expanding head. The electric motor is connected to a power source, in particular a battery, and a control unit.The control unit is designed to implement the method as described above. Preferably, the expansion device does not have a pressure sensor. By detecting the pressure, it is also possible to determine when the end of the travel has been reached, and the point in time at which the expansion process is interrupted can also be controlled using the detected pressure. However, pressure sensors are expensive and prone to errors, so that these are precisely avoided by the steps of the method of the present invention and in particular by the control unit of the present invention. Thus, an expansion device is created which does not have a pressure sensor. Furthermore, the present invention relates to a pipe connection between a first pipe and a second pipe or a pipe fitting, wherein one pipe end of the first pipe is expanded using an expansion device as described above, and one pipe end of the second pipe or the pipe fitting is inserted.In particular, the first pipe is a plastic pipe. Preferably, the plastic pipe is a PE pipe, a PVC pipe, or a CPVC pipe. Preferably, the plastic pipe is a cross-linked polyethylene pipe (PE-X). Alternatively, the first pipe and / or the second pipe is a metal pipe, in particular a copper pipe. Furthermore, the present invention relates to a method for connecting a first pipe and a second pipe or pipe fitting, which is in particular an axial pipe connection. For this purpose, a pipe end of the first pipe is expanded according to the method described above, and subsequently a pipe end of the second pipe or the pipe fitting is inserted. In particular, a sleeve or sleeve is subsequently pushed over the expanded pipe end section of the first pipe.The invention is explained in more detail below using preferred embodiments with reference to the attached drawings. The figures show: Figs. 1A - 1D an axial pipe connection according to the prior art, Fig. 2 an expander according to the present invention, Fig. 3 the inventive method for expanding a pipe and Fig. 4 an exemplary current flow during an expansion run according to the present invention. Reference is made below to Fig. 2. The expander 16 according to the invention has an expander head 18, onto which a pipe 10 is pushed with its end. The expander head 18 has at least two or more independently radially movable expander sections 20, which together form a cylindrical or substantially cylindrical outer surface that engages with the inner surface of the pipe 10. Furthermore, the expander head 18 has a wedge 22.The wedge 22 is connected to an electric motor 24 and is displaced in the direction of arrow 30 in the illustration in Fig. 2 during the expansion process. As a result, the expansion sections 20 move radially outward according to the arrows 32 and expand the pipe 10. The present invention is not limited to a specific technology or mechanism for expanding the pipe. Other possibilities can of course also be combined with the method of the present invention. Furthermore, the electric motor 24 is connected to a power supply 26, which is designed, for example, as a battery. The electric motor 24 is also connected to a control unit 28, which controls the electric motor 24 and, in particular, monitors the timing of the expansion process. Even if only one electric motor 24 is shown in Fig. 2, the expansion device 16 can be designed as an electro-hydraulic expansion device.In this case, the movement of the electric motor 24 is converted into a hydraulic force, the wedge 22 being moved by means of the hydraulic force to generate a sufficiently large expansion force for expanding the pipe 10. Reference is made below to Fig. 3, which discloses the steps of the method according to the invention. In step S01, the electric motor 24 of the power tool or of the expanding device 16 is started. The pipe 10 to be expanded can already be connected to the expanding head 18 of the expanding device 16. In step S02, a current ^ of the electric motor 24 is detected. The detection can take place continuously or at a time interval. In step S03, if a predetermined current limit value ^^ is exceeded, the electric motor 24 is switched off for a predetermined holding time Δ^. In step S04, after the predetermined holding time Δ^ has elapsed, the electric motor 24 is started and the work process orthe expansion travel is continued. In step S05, when the end of the travel is reached, the electric motor 24 is switched off again. Thus, according to the method according to the invention, a current limit value ^^ is used. If this predetermined current limit value ^^ is exceeded by the current ^ of the electric motor 24, the electric motor 24 is switched off for a predetermined holding time Δ^. After the predetermined holding time Δ^ has elapsed, the electric motor 24 is restarted and the expansion travel is completed or carried out until its end. If the expander 16 is an electro-hydraulic expander, a hydraulic valve (not shown) is opened when the end of the travel is reached. As a result, the pressure in the hydraulic chamber drops, in particular suddenly. At the same time, the speed of the electric motor increases. Based on the increase in the speed of the electric motor 24, the motor can then be switched off.Reference is made below to Fig. 4, which shows an exemplary and schematic representation of the current profile ^ (curve 34) over time t during an expansion run. After the electric motor 24 starts, a starting current 36 is initially generated, which then recurs. After the starting current 36 drops, the temperature ^ and the average voltage ^ are measured in an exemplary interval 38. ^ The average voltage ^ ^for example, from the charge level of the battery, which serves as the power supply. The temperature ^ is the ambient temperature. The ambient temperature has a significant influence on the elastic properties of a plastic pipe. However, the temperature also affects the operation of the electrical device. These influences on the expansion process can be taken into account by recording the temperature, thus ensuring consistent expansion of the pipe 10 even under different influences. From the average stress ^ ^ and the temperature ^ is then an expected holding time ^ Halt The expected holding time ^ Halt be determined using a polynomial ^ Halt ^^ ^ ^, where the polynomial is in particular of degree 2, of degree 3 or higher. Preferably, the expected holding time ^ Halt determined by To take the temperature into account, the coefficients of the individual monomials of the polynomial depend quadratically on the temperature and are given by: ^=^(^)=^^^ 2 +^^^+^^ ^=^(^)=^ ^ ^ 2 +^ ^ ^+^ ^ Other dependencies, such as a linear dependency or a dependency on temperature with a higher power, are also possible. This results in the expected holding time ^ Halt depending on the average voltage ^ ^ and ^ to: with the coefficients ^ ^ : between 10 -6 and 10 -5 , especially between 6*10 -6 and 7*10 -6 ; ^ ^ : between -10 -4 and -10 -3 , especially between -10 -4 and -2*10 -4 ; ^ ^ : between -10 -2 and -10 -1 , especially between -2*10 -2 and -4*10 -2 ; ^ ^ : between -10 -4and -10 -3 , especially between -10 -4 and -2*10 -4 ; ^ ^ : between 10 -3 and 10 -2 , especially between 2*10 -3 and 4*10 -3 ; ^ ^ : between 1 and 5, especially between 1 and 2; ^ ^ : between 10 -3 and 10 -2 , especially between 10 -3 and 2*10 -3 ; ^ ^ : between -10 -2 and -10 -1 , especially between -10 -2 and -2*10 -2 ; ^ ^ : between -10 and -20, especially between -12 and -14; ^ ^ : between -10 -3 and -10 -2 , especially between -10 -3 and -2*10 -3 ; ^ ^ : between -10 -4 and -10 -3 , especially between -2*10 -4 and -3*10 -4 ; ^ ^: between 10 and 100, in particular between 40 and 60. In order to take into account production-related deviations of the electric motor and / or the expander, such as wear, a correction term can be taken into account. This correction term can be determined by a calibration run, in particular without tools and preferably without the expander head 18. Since a constant correction value P may not be sufficient for the various temperature conditions, the correction value depends on the temperature. The correction value P is linear, quadratic, or with a higher power dependent on the temperature T. In particular, the correction value is given by , where the calibration time tkal corresponds to the expected holding time during the calibration run, which is analogous to ^ Halt determined, especially without a correction term. In other words, ^ ^^^the time until the characteristic reference point (beginning of the current rise). Furthermore, tAN indicates the actual temporal position of the force increase, so that the device-specific correction value P can be determined from this. The coefficients k1, k2, k3 are: ^1: between -10 -5 and -10 -4 , especially between -5*10 -5 and -6*10 -5 ; ^2: between 10 -3 and 10 -2 , especially between 5*10 -3 and 6*10 -3 ; ^3: between 0.01 and 0.2, in particular between 0.1 and 0.12. Taking into account the device-specific correction value P, the expected holding time ^ Halt to Before reaching the expected holding time ^ Halt the mean current ^̃ is measured at time 40. This can occur less than 1 second before reaching the previously calculated expected holding time ^ Halt When the expected holding time is reached ^ Haltthe motor current is reduced to slow down the expansion process and furthermore only after reaching the expected holding time ^ Haltthe current ^ of the electric motor can be detected. As shown in Fig. 4, the current is then reduced, with the current i subsequently increasing 42 as the pipe 10 expands due to the increasing force required to expand the pipe 10. When a predetermined current limit value ^^ (reference numeral 44) is reached, the electric motor 24 is switched off for a predetermined holding time Δ^ (reference numeral 46). The predetermined holding time Δ^ is in particular between 1 and 5 seconds and preferably between 1 and 2 seconds. After the predetermined holding time Δ^ has elapsed, the electric motor 24 is switched on again. This again results in a starting current 48, and after this current drops, the current continues to rise due to the continued expansion process of the pipe 10. At the end 50 of the expansion travel, the current drops and the electric motor 24 can be switched off. The expansion process is complete.Due to the specified holding time Δ^, the elastic recovery of the pipe 10 is delayed. Thus, the pipe 10 can be easily placed onto the pipe fitting 14 or a second pipe to ensure a secure axial connection of the pipes.

Claims

Patent claims 1. Method for controlling a power tool, in particular an electro-hydraulic expander, implemented in the power tool, the method comprising the steps of: a) starting an electric motor of the power tool; b) detecting a current ^ of the electric motor; c) upon exceeding a predetermined current limit value ^^, switching off the electric motor for a predetermined holding time Δ^; d) after expiration of the predetermined holding time Δ^, starting the electric motor until the end of the travel; e) switching off the electric motor upon reaching the end of the travel.

2. Method according to claim 1, wherein an expected holding time ^ Halt is determined and in particular the current ^ of the electric motor is recorded when the expected holding time ^ is reached Halt 3. Method according to claim 2, wherein upon reaching the expected holding time ^ Haltthe motor speed or current of the electric motor is reduced, in particular by adjusting the pulse width modulation.

4. Method according to claim 2 or 3, in which before reaching the expected holding time ^ Halt an average current ^̃ is detected, wherein the current limit value ^^ is dependent on the average current ^̃ and is in particular 0.5 to 1 times the average current ^̃ and preferably 0.6 to 0.8 times the average current ^̃.

5. A method according to any one of claims 1 to 4, wherein the expected holding time ^ Halt depends on a mean voltage ^ ^ and a temperature ^, whereby in particular immediately after starting the electric motor the average voltage ^ ^ and the temperature ^ are detected, preferably after the starting current has dropped.

6. Method according to claim 5, wherein the expected holding time ^ Halt is determined using a polynomial ^ Halt ^ ^^^ , wherein the polynomial is in particular of degree 3 or higher.

7. The method according to claim 6, wherein the polynomial ^ Halt ^^ ^ ^ coefficients which depend in particular linearly, quadratically or with a higher power on the temperature ^.

8. Method according to one of claims 2 to 7, in which the expected holding time ^ Haltis adjusted by means of a device-specific correction value ^, wherein the device-specific correction value is determined by means of a calibration run.

9. Method according to claim 8, in which the calibration run is carried out without a tool and in particular without an expanding head.

10. Method according to claim 8 or 9, in which the correction value ^ depends linearly, quadratically or with a higher power on the temperature ^.

11. Method according to one of claims 1 to 10, in which the predetermined holding time Δ^ is between 1 s and 5 s, in particular between 1 s and 2 s.

12. Method according to one of claims 1 to 11, in which when the end of the run is reached, a hydraulic valve opens and the electric motor switches off.

13. An expander with an expander head for expanding pipe ends and an electric motor for actuating the expander head, wherein the electric motor is connected to a power source, in particular a battery, and a control unit, wherein the control unit is designed to implement the method according to one of claims 1 to 12.

14. An expander according to claim 13, characterized in that it does not have a pressure sensor.

15. A pipe connection of a first pipe and a second pipe or pipe fitting, wherein a pipe end of the first pipe is expanded with an expander according to claim 13 or 14, and a pipe end of the second pipe or the pipe fitting is inserted.Method for connecting a first pipe and a second pipe or pipe fitting, wherein a pipe end of the first pipe is widened according to the method according to one of claims 1 to 12 and subsequently a pipe end of the second pipe or the pipe fitting is inserted.

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