Electric hand tool with torque sensor and external magnetic field compensation

Abstract

To solve the problem that since a magnetostrictive / magnetoelastic torque measurement sensor, in most cases, uses one or more coils for magnetic flux measurement, external magnetic fields may interfere with a measurement signal of the sensor.SOLUTION: An electric hand tool includes: a drive unit for driving a shaft of the electric hand tool, where the drive unit is configured to drive a socket via the shaft; a magnetostrictive torque sensor for measuring torque applied to the shaft via the drive unit, where the magnetostrictive torque sensor includes a magnetized torque transfer component and a 3D magnetic field sensor, where the 3D magnetic field sensor is configured to measure a total magnetic field, where the total magnetic field includes magnetic field generated by a magnetized portion of the magnetized shaft and interfering external magnetic field; and a processor for at least partially correcting the total magnetic field with respect to the interfering external magnetic field and acquiring the corrected magnetic field corresponding to the magnetic field generated by the magnetized torque transfer component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric hand tool equipped with a torque sensor. [Background technology]

[0002] Torquing of vehicle nuts or bolts, such as for wheel mounting, is done manually by a mechanic in the workshop using a mechanical torque wrench, with the maximum torque for each set by a mechanical slip clutch or pneumatically.

[0003] Furthermore, there are also power hand tools, such as impact wrenches, that allow the required torque to be preset. A particular type of such power hand tool has a magnetostrictive / magnetoelastic torque measuring sensor, as described in US Pat. No. 5,399,366. Sensors based on magnetoelastic principles often use one or more coils for magnetic flux measurement. However, external magnetic fields can interfere with the measurement signal of the sensor. Such external magnetic fields are due to the Earth's magnetic field, for example strong currents, electromagnetic radiation from nearby electric motors or magnetized parts. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent Application Publication No. 4173753 A1 Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to overcome at least some of the above mentioned drawbacks. [Means for solving the problem]

[0006] This object is achieved by the electric hand tool according to claim 1.

[0007] The electric hand tool according to the invention, in particular an impact wrench or a screwdriver or an electric drill, comprises a drive unit for driving a shaft of the electric hand tool, the drive unit being configured to drive a socket of the electric hand tool or a socket connectable to the electric hand tool via the shaft, and a magnetostrictive torque sensor for measuring a torque applied to the shaft via the drive unit, the magnetostrictive torque sensor being coupled to a magnetized torque transmission part, such as a magnetized part of the shaft, and a 3D magnetic field sensor, in particular a magnetoresistive sensor, for example an AMR (anisotropic magnetoresistance), TMR (tunnel magnetoresistance), CMR (colossal magnetoresistance), GMR (giant magnetoresistance) or EMR (extraordinary magnetoresistance). the 3D magnetic field sensor being configured to measure a total magnetic field, the total magnetic field including a magnetic field generated by the magnetized torque transmitting part and an interfering external magnetic field; and a processor for at least partially correcting the total magnetic field against the interfering external magnetic field to obtain a corrected magnetic field corresponding to the magnetic field generated by the magnetized torque transmitting part, and for determining a torque applied to the shaft via the drive unit based on the corrected magnetic field.

[0008] Measurements with magnetostrictive torque sensors can therefore compensate for the effects of interference from external magnetic fields not resulting from the magnetized parts of the shaft, in particular magnetic fields having a different direction than the magnetic field arising from the magnetized shaft due to the magnetostrictive effect, and therefore the torque applied to the shaft can be determined more accurately.

[0009] According to one development, the torque results from a rotational force acting on the shaft via the drive unit and a counter-rotational force acting on the shaft via the socket.

[0010] The external magnetic field is measured by the 3D magnetic field sensor in the absence of torque on the shaft and zero counter-rotational force acting on the shaft through the socket. This has the advantage that the external magnetic field can be determined separately, since there is no influence (magnetic field) from the magnetostrictive torque sensor. The shaft may be stationary or may be rotating at a constant rotational speed because it is driven by an electric motor.

[0011] In another development, the power hand tool further comprises an angle sensor for determining a rotation angle of the shaft.

[0012] The external magnetic field is measured by a 3D magnetic field sensor depending on the rotation angle of the shaft determined by the angle sensor. This has the advantage that external magnetic fields from sources that are rotationally asymmetric with respect to the rotation of the shaft can be determined. For example, a magnetized nut mounted in a socket is pre-magnetized so that it is not rotationally symmetric.

[0013] The electric hand tool further comprises a memory in communication with the processor, the memory configured to store a relationship between the 3D value of the external magnetic field and the rotation angle of the shaft, and the processor configured to obtain the interfering external magnetic field according to the rotation angle based on the stored relationship.

[0014] In another development, the socket is configured to receive a fastening element such as a nut, bolt or screw.

[0015] In a further development, the external magnetic field is generated by at least one of the following group: a current, electromagnetic radiation, for example from an electric motor, or a magnetized component, in particular a socket, a tool or a fastening element connected to the socket, an electric motor of a power hand tool, and the earth's magnetic field.

[0016] This stated object is also achieved by a method according to claim 9.

[0017] A method for measuring torque in a power hand tool, in particular an impact wrench or a screwdriver or a power drill, comprises the steps of driving a shaft of the power hand tool and driving a socket of the power hand tool or a socket connected to the power hand tool via the shaft, and measuring the torque applied to the shaft via the drive unit using a magnetostrictive torque sensor, the magnetostrictive torque sensor comprising a magnetized torque transmitting part, such as a magnetized portion of the shaft, and a 3D magnetic field sensor, in particular a magnetoresistive sensor, for example a TMR, CMR, GMR, AMR or EMR magnetic field sensor, and by using the 3D magnetic field sensor, measuring a total magnetic field, the total magnetic field including the magnetic field generated by the magnetized torque transmitting part and an interfering external magnetic field, and at least partially correcting the total magnetic field for the interfering external magnetic field to obtain a corrected magnetic field corresponding to the magnetic field generated by the magnetized torque transmitting part, and determining the torque applied to the shaft via the drive unit based on the corrected magnetic field.

[0018] According to one development of the method according to the invention, the torque is due to a rotational force acting on the shaft via the drive unit and a counter-rotational force acting on the shaft via the socket, the method further comprising a step of measuring the external magnetic field by the 3D magnetic field sensor in a state where there is no torque on the shaft, and the counter-rotational force acting on the shaft via the socket is zero.

[0019] In another development, the method further comprises the steps of determining a rotation angle of the shaft and measuring an external magnetic field by the 3D magnetic field sensor as a function of the determined rotation angle of the shaft.

[0020] The method further includes storing in a memory a relationship between the 3D value of the external magnetic field and the rotation angle of the shaft, and obtaining the interfering external magnetic field according to the rotation angle based on the stored relationship.

[0021] In another development, the socket can receive a fastening element such as a nut, bolt or screw.

[0022] In a further development, the external magnetic field is generated by at least one of the following group: a current, electromagnetic radiation, for example from an electric motor, or a magnetized component, in particular a socket, a tool or a fastening element connected to the socket, an electric motor of a power hand tool, and the earth's magnetic field.

[0023] Further features and exemplary embodiments and advantages of the present invention are described in more detail below with the aid of the following drawings. It is clear that the embodiments do not cover the entire field of the present invention. Moreover, it is clear that some or all of the features described below can also be combined with each other in different ways. [Brief description of the drawings]

[0024] [Figure 1] 1 illustrates one embodiment of a power hand tool according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] When torque sensors measuring based on the magnetoelastic effect are used in power tools / machine tools (e.g. impact wrenches), external magnetic fields can cause measurement errors or even make the measurement impossible. Impact wrenches often use slip-on nuts or other slip-on tools that are pre-magnetized by the manufacturer. Furthermore, these machines are often driven by powerful electric motors, which, due to their high power consumption and associated currents, generate strong magnetic fields that are superimposed on the (desired) magnetic field produced by inverse magnetostriction.

[0026] Sensors based on magnetoelastic principles often use one or more coils for magnetic flux measurement. However, the coils can only measure the value of the magnetic flux, not the direction of the magnetic flux (no 3D measurements).

[0027] AMR, TMR, GMR, CMR or EMR sensors (3D resolution) are able to detect the magnetic flux direction. By using such sensors instead of induction coils, the field direction of the magnetic flux can be detected. It is therefore possible to distinguish whether a signal is caused by the Earth's magnetic field, by a magnetized part (e.g. a stationary or rotating wrench socket) or by a torque applied to the shaft of an impact wrench (which can be measured) due to the magnetoelastic effect. The invention therefore relates in particular to the use of a direction resolving element such as an AMR sensor for use in machine tools to correct / compensate for errors due to external magnetic fields.

[0028] FIG. 1 illustrates one embodiment of a power hand tool 100 in accordance with the present invention.

[0029] The power hand tool 100 comprises a drive unit (electric motor) 10 for driving a shaft 20 of the power hand tool 100, the drive unit 10 being configured to drive a socket 30 connectable to the power hand tool 100 via the shaft 20. The power hand tool 100 further comprises a magnetostrictive torque sensor 40 for measuring a torque applied to the shaft 20 via the drive unit 10, the magnetostrictive torque sensor 40 comprising a magnetized portion 41 of the shaft 20 and an AMR, TMR, GMR, CMR or EMR magnetic field sensor 42 configured to measure a total magnetic field, the total magnetic field including the magnetic field generated by the magnetized portion of the shaft and the interfering external magnetic field. In addition, a processor 50 is provided for at least partially correcting the total magnetic field against the interfering external magnetic field to obtain a corrected magnetic field corresponding to the magnetic field generated by the magnetized portion 41 of the shaft 20 and for determining the torque applied to the shaft 20 via the drive unit 10 based on the corrected magnetic field.

[0030] The external magnetic field can be measured by the AMR, TMR, GMR, CMR or EMR magnetic field sensor 42 in the absence of torque on the shaft 20, where there is zero counter-rotational force acting on the shaft 20 through the socket 30. This results in the absence of any influence (magnetic field) from the magnetostrictive torque sensor, so that the external magnetic field can be determined separately. The shaft 20 can be stationary or can be rotating at a constant rotational speed by being driven by the electric motor 10.

[0031] The power hand tool 100 further comprises an angle sensor 11 for determining the rotation angle of the shaft 20. The external magnetic field is measured by an AMR, TMR, GMR, CMR or EMR magnetic field sensor 42 depending on the rotation angle of the shaft determined by the angle sensor 11. This allows determining an external magnetic field from a source that is rotationally asymmetric with respect to the rotation of the shaft. For example, the magnetized nut mounted in the socket 30 is pre-magnetized so that it is not rotationally symmetric.

[0032] The electric hand tool 100 further comprises a memory 51 (volatile or permanent) in communication with the processor 50. The memory 51 stores a current relationship between the 3D values ​​of the external magnetic field and the rotation angle of the shaft 20, and the processor 50 can obtain the interfering external magnetic field depending on the rotation angle based on the stored relationship. This relationship depends on the orientation of the electric hand tool 100, for example, when the influence of the earth's magnetic field is compensated. Furthermore, this relationship depends on the particular magnetized fastening element 31 or magnetized socket 30 that is attached.

[0033] In this embodiment, the power hand tool 100 has a rechargeable battery unit 91 mounted in the housing 90 for supplying electrical energy to the drive unit 10. In this example, the battery unit 91 is mounted in a hand grip 92 of the housing 90.

[0034] The socket 30 can accept a fastening element 31, such as a nut, bolt or screw, which can be driven to fasten to an object. The processor 50 receives the measurement signal from the magnetostrictive torque sensor 40 and controls the drive unit 10 to adjust the applied torque value by increasing the torque until it is within a predefined tolerance range around a predetermined value used for the current fastening process. The predetermined value and / or the tolerance range are stored in the persistent memory 65 of the power hand tool 100.

[0035] The torque sensor 40 is a magnetostrictive torque sensor and comprises a magnetised portion 41 on the shaft 20 and an AMR, TMR, GMR, CMR or EMR magnetic field sensor 42 for detecting magnetic field changes from the magnetised portion 41 outside the shaft 20 .

[0036] The driven shaft 20 is magnetized and an AMR, TMR, GMR, CMR or EMR magnetic field sensor 42 is provided near the magnetized portion 41 to determine the magnetic field change when torque is applied, which torque causes a twisting of the shaft 20, thereby generating a magnetic field change at the location of the magnetic field sensor due to the inverse magnetostrictive effect. The magnetization of the shaft 20 may be provided during manufacture of the power hand tool 100 and a calibration of the magnetic field sensor signal related to the applied torque is stored in the persistent memory 65 of the power hand tool 100.

[0037] A torque sensor based on the principle of the inverse magnetostriction effect is described, for example, in EP 3050790 B1. A magnetized shaft (as the primary sensor part) generates a magnetic field outside the shaft in response to an applied torque, which can be detected contactlessly by a magnetic field sensor (as the secondary sensor part). The change in the magnetic field is usually directly proportional to the applied torque. During the manufacturing phase of the torque sensor, a corresponding one-time calibration is performed in order to relate the change in the magnetic field to the applied torque.

[0038] Other magnetized torque transmission parts based on the inverse magnetostrictive effect are described in EP 4116688 A1 and can be used as an alternative in the electric hand tool 100 instead of the magnetized part 41 of the shaft 20. These torque sensors comprise a disk containing a magnetostrictive material, a pre-magnetized material or a magnetizable material, and a magnetic field sensor arrangement, where a torque acting around the rotation axis of the disk is applied to the disk, the magnetostrictive material is designed to generate a magnetic field outside the disk that varies depending on the applied torque, the magnetic field sensor arrangement is designed to output a signal based on the magnetic field generated by the magnetostrictive material, and the torque sensor is configured to determine the value of the applied torque based on the output signal. The disk acting as the torque transmission part is used to measure the applied torque by pre-magnetizing at least a part of the disk. In particular, the disk has spokes connecting an inner part and an outer part of the disk, one or more of the spokes being magnetized. In this way, the disk is used as the primary sensor, rather than the shaft on which it is arranged.

[0039] The embodiments are exemplary only, the full scope of the invention is defined by the claims.

Claims

1. An electric hand tool, in particular an impact wrench or a screwdriver or an electric drill, a drive unit for driving a shaft of the electric hand tool, the drive unit being configured to drive a socket of the electric hand tool or a socket connectable to the electric hand tool via the shaft; a magnetostrictive torque sensor for measuring a torque applied to the shaft via the drive unit, the magnetostrictive torque sensor comprising a magnetized torque transmitting part, such as a magnetized portion of the shaft, and a 3D magnetic field sensor, in particular an AMR, TMR, GMR, CMR or EMR magnetic field sensor, the 3D magnetic field sensor being configured to measure a total magnetic field, the total magnetic field including the magnetic field generated by the magnetized torque transmitting part and interfering external magnetic fields; a processor for at least partially compensating the total magnetic field against the interfering external magnetic field to obtain a compensated magnetic field corresponding to the magnetic field generated by the magnetized torque transfer portion, and for determining the torque applied to the shaft via the drive unit based on the compensated magnetic field. An electric hand tool having

2. The power hand tool of claim 1 , wherein the torque results from a rotational force acting on the shaft through the drive unit and a counter rotational force acting on the shaft through the socket.

3. The power hand tool of claim 2 , wherein the external magnetic field is measured by the 3D magnetic field sensor in a state where there is no torque on the shaft, and the counter-rotation force acting on the shaft through the socket is zero.

4. The power hand tool according to any one of claims 1 to 3, further comprising an angle sensor for determining a rotation angle of the shaft.

5. The power hand tool of claim 4 , wherein the external magnetic field is measured by the 3D magnetic field sensor in response to the rotation angle of the shaft determined by the angle sensor.

6. 6. The power hand tool of claim 5, further comprising a memory in communication with the processor, the memory configured to store a relationship between 3D values ​​of the external magnetic field and the rotation angle of the shaft, and the processor configured to obtain the interfering external magnetic field as a function of the rotation angle based on the stored relationship.

7. The power hand tool according to any one of the preceding claims, wherein the socket is configured to receive a fastening element such as a nut, bolt or screw.

8. The electric hand tool according to any one of claims 1 to 7, wherein the external magnetic field is generated by at least one of the following group: a current, electromagnetic radiation, or a magnetized component, for example from an electric motor, in particular the socket, a tool or a fastening element connected to the socket, an electric motor of the electric hand tool, and the earth's magnetic field.

9. A method for measuring torque in a power hand tool, in particular an impact wrench or a screwdriver or a power drill, comprising the steps of: driving a shaft of the power hand tool and driving a socket of the power hand tool or a socket connected to the power hand tool via the shaft; measuring the torque applied to the shaft via the drive unit using a magnetostrictive torque sensor, the magnetostrictive torque sensor comprising a magnetized torque transmitting part, such as a magnetized portion of the shaft, and a 3D magnetic field sensor, in particular an AMR, TMR, GMR, CMR or EMR magnetic field sensor, and using the 3D magnetic field sensor to measure a total magnetic field, the total magnetic field including the magnetic field generated by the magnetized torque transmitting part and interfering external magnetic fields; at least partially compensating the total magnetic field against the interfering external magnetic field to obtain a compensated magnetic field corresponding to the magnetic field generated by the magnetized torque transmitting part, and determining the torque applied to the shaft via the drive unit based on the compensated magnetic field. A method comprising:

10. 10. The method of claim 9, wherein the torque is due to a rotational force acting on the shaft through the drive unit and a counter-rotational force acting on the shaft through the socket, the method further comprising measuring the external magnetic field with the 3D magnetic field sensor in a state where there is no torque on the shaft, and the counter-rotational force acting on the shaft through the socket is zero.

11. The method according to claim 9 or 10, further comprising the steps of determining a rotation angle of the shaft and measuring the external magnetic field by the 3D magnetic field sensor in response to the determined rotation angle of the shaft.

12. 12. The method of claim 11, further comprising the steps of: storing in a memory a relationship between the 3D values ​​of the external magnetic field and the rotation angle of the shaft; and obtaining the interfering external magnetic field as a function of the rotation angle based on the stored relationship.

13. The method according to any one of claims 9 to 12, wherein the socket receives a fastening element such as a nut, bolt or screw.

14. The method according to any one of claims 9 to 13, wherein the external magnetic field is generated by at least one from the group of: a current, electromagnetic radiation, for example from an electric motor, or a magnetized component, in particular the socket, a tool or a fastening element connected to the socket, an electric motor of the power hand tool, and the earth's magnetic field.

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