Control circuit for the linear speed control of a hand tool, and hand tool comprising such a control circuit

Abstract

The invention relates to a control circuit (1) for the linear speed control of an electrically operated hand tool, the control circuit comprising: a magnetic field sensor (20) for detecting a magnetic field; and a slider (30) which can be displaced relative to the magnetic field sensor (20) from a start point (11) to an end point (12) along a linear actuation path (10), wherein the magnetic field sensor (20) is positioned along the actuation path (10), and a bar magnet (31) is fixed to the slider (30) parallel to the actuation path (10), wherein a soft-magnetic core (32) is arranged on a side of the magnetic field sensor (20) facing away from the bar magnet (31), and a magnetic field established between the bar magnet (31) and the soft-magnetic core (32) is linearly detectable by the magnetic field sensor (20) during movement of the slider (30) from the start point (11) to the end point (12) for speed control, and is output by the magnetic field sensor (20) as a linearly varying output signal (43).

Description

[0001] Marquardt GmbH

[0002] P 591 PCT KN

[0003] Control circuit for linear speed control of a hand tool and hand tool with such a control circuit

[0004] Description:

[0005] The invention relates to a control circuit for linear speed control of an electrically operated hand tool and a hand tool with such a control circuit.

[0006] A wide variety of electrically operated hand tools are known from the state of the art, which often have an electric motor whose speed is to be controlled by an operator.

[0007] For more intuitive operation, it is usually intended that the speed of the electric motor should be linearly variable or the hand tool linearly controllable. Basically, two variants are common for this. The first uses a circuit based on electrical contacts, in which a wiper moves along a circuit carrier, touching contacts and, in particular, a resistance strip. However, this leads to high mechanical wear due to the direct contact, and the mechanical contact is also susceptible to vibrations, so that, at least under certain vibration conditions, a continuous output signal cannot always be generated with wipers.

[0008] As an alternative option and for example from the documents

[0009] DE00001975685701 , DE00001962423301 and DE000010303363A1 as well as from the currently unpublished German patent application with file number 10 2024 105 411.5 it is also known to move a slider with one or two magnets and a magnetic field sensor relative to each other and to generate an output signal based on the magnetic field measured by the magnetic field sensor.

[0010] However, variants that rely solely on a magnet are sometimes problematic, as the magnetic field generated by a single magnet is only approximately linear within a very limited range. This means the actuation range—the range in which a linearly changing magnetic field can be detected by the magnetic field sensor—is very short. If the actuation range extends beyond this limited range, the essentially sinusoidal output signal of the magnetic field sensor must be converted into a linear signal by additional electronics, which is correspondingly complex and expensive.

[0011] Variants based on two magnets are significantly more suitable in this respect, since the magnetic field between the magnets changes linearly over a larger area and preferably over almost the entire actuation path, so that the output signal of the magnetic field sensor does not have to be converted into a linearly changing signal or only to a minor extent.

[0012] Nevertheless, such a solution is disadvantageous due to comparatively high manufacturing costs as well as design and space-related limitations, which can arise in particular from the two magnets arranged parallel to each other.

[0013] The invention is therefore based on the objective of overcoming the aforementioned disadvantages and providing a control circuit for the linear speed control of a hand tool or a hand tool with such a control circuit, by which the hand tool can be controlled linearly along a comparatively long actuation path in a simple and cost-effective manner as well as with little or no wear.

[0014] This problem is solved by the combination of features according to claim 1.

[0015] According to the invention, a control circuit is proposed, particularly for an operating device of an electrically operated hand tool and for the linear speed control of an electrically operated hand tool, and preferably of an electric motor of an electrically operated hand tool or its rotational speed. The control circuit comprises a magnetic field sensor for detecting a magnetic field and a slider that is movable from a starting point to an end point along a linear actuation path relative to the magnetic field sensor. The magnetic field sensor is arranged along the actuation path, and a bar magnet, preferably a single bar magnet, is fixed to the slider parallel to the actuation path. Furthermore, a soft magnetic core is arranged on a side of the magnetic field sensor facing away from the bar magnet.This creates a magnetic field between the bar magnet and the soft magnetic core, which can be detected by the magnetic field sensor and which changes essentially linearly depending on the path taken when the slider moves from the starting point to the end point, so that the magnetic field or its change can be detected linearly by the magnetic field sensor for speed control and output by the magnetic field sensor as a linearly changing output signal.

[0016] In contrast to other solutions known in the prior art, it should be noted that the magnetic field is formed between the bar magnet and the soft magnetic core and changes due to the relative movement of the bar magnet to the soft magnetic core, which is stationary on the control circuit. Thus, the magnetic field is not merely shifted by the movement of the slider, but actually changes. The magnetic field, and therefore the change in the magnetic field, can be detected by the magnetic field sensor, which is also stationary on the control circuit.

[0017] Although the orientation of the bar magnet, which can also be referred to simply as a magnet in the following, is not essential for the core of the present invention, it has proven advantageous if an end face forming a north pole of the magnet is located closer to the soft magnetic core or the magnetic field sensor along the actuation path.

[0018] An advantageous embodiment of the invention provides that the soft magnetic core is stationary relative to the magnetic field sensor, wherein preferably both the soft magnetic core and the magnetic field sensor are stationary relative to a circuit carrier mentioned later, the bar magnet being fixed to the slider and thus displaceable with it along the actuation path relative to the soft magnetic core and the magnetic field sensor. Preferably, the soft magnetic core extends along and parallel to the actuation path, wherein alternatively or additionally it can be provided that the soft magnetic core has a length along the actuation path equal to half the path length from the starting point to the endpoint along the actuation path, so that the soft magnetic core is half as long as the actuation path.It can further be provided that the actuation path from the starting point to the end point has a first half and a subsequent second half, i.e., is divided into two halves of equal length, wherein the soft magnetic core and / or the magnetic field sensor are arranged in the second half and preferably centrally or in the middle of the second half.

[0019] Assuming that the length of the soft magnetic core extends to half the total length of the actuation path and is positioned centrally within the second half of the actuation path, it completely covers this second half. If the bar magnet is arranged on the slider such that an end face of the bar magnet facing the magnetic field sensor is located at the starting point of the slider and is moved to the end point with the slider, this advantageous arrangement results in a minimal distance between the end face of the bar magnet at the end point and the parallel end face of the soft magnetic core, thus maximizing the magnetic field strength.

[0020] By way of example, the total length of the actuation path from start point to end point can be 5 mm or preferably 4.5 mm, from which a respective advantageous length extension of the soft magnetic core and the bar magnet can be derived.

[0021] Furthermore, the control circuit can also include a circuit carrier extending parallel to the actuation path, preferably a printed circuit board. The magnetic field sensor and / or the soft magnetic core are arranged and fixed on the circuit carrier and are thus fixed in position relative to each other and to the circuit carrier. The magnetic field sensor and the soft magnetic core are further arranged and fixed on two opposite sides of the circuit carrier, and are particularly preferably centered relative to each other, so that their respective centers coincide when viewed from above.

[0022] The circuit carrier preferably also has contact surfaces which correspond to the magnetic field sensor and / or the soft magnetic core, wherein the magnetic field sensor or the soft magnetic core is designed as a surface mountable device (SMD) and is fixed to the circuit carrier via the contact surfaces.

[0023] Preferably, the magnetic field sensor is a Hall sensor, and in particular a linear Hall sensor.

[0024] Regarding the soft magnetic core, it should be noted that it is preferably formed or shaped in a plate-like form, i.e., larger in the width and length directions than in the thickness direction, and / or in a rod-like form, i.e., larger in the length direction than in the width and thickness directions. Furthermore, the soft magnetic core is preferably formed from at least one electrical steel sheet and, in particular, from an iron-silicon alloy.

[0025] The bar magnet preferably has a length that corresponds to or is greater than the path length from the starting point to the end point.

[0026] In an advantageous embodiment, the magnetic field sensor is configured to output a voltage as an output signal, which changes linearly as the slider moves from the starting point to the end point due to the change in the magnetic field formed between the bar magnet and the soft magnetic core, depending on the distance traveled.

[0027] To simplify operation, the slider is preferably spring-returned to the starting point and / or kinematically connected to an actuating element that can be operated by an operator.

[0028] In order to prevent or at least minimize a variation of the magnetic field due to a movement orthogonal to the actuation path, in an advantageous variant at least one guide body is provided on the slider which is held without contact with the magnetic field sensor, by which a distance of the bar magnet to the magnetic field sensor and / or the soft magnetic core is maintained that is orthogonal to the actuation path or to the circuit carrier.

[0029] Another aspect of the invention relates to an electrically operated hand tool with an electric motor and a control circuit according to the invention, wherein the electric motor is controlled or controllable by the output signal of the magnetic field sensor.

[0030] The features disclosed above can be combined in any way, provided that this is technically possible and they do not contradict each other.

[0031] Other advantageous embodiments of the invention are characterized in the dependent claims or are described in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. The figures show:

[0032] Fig. 1 a control circuit; Fig. 2 a magnetic field between a bar magnet and a soft magnetic core, a resulting course of a field strength determined between these, and an output voltage generated therefrom serving as an output signal.

[0033] The figures are schematic examples. Identical reference symbols in the figures indicate identical functional and / or structural features.

[0034] Figure 1 shows a basic structure of a control circuit 1 proposed according to the invention. This circuit has a magnetic field sensor 20 designed as a linear Hall sensor, which is arranged on a circuit carrier 21 and electrically contacted.

[0035] A slide 30 is provided that is movable relative to the magnetic field sensor 20 and is linearly displaceable along the actuation path 10. A bar magnet 31, extending parallel to the actuation path 10, is fixed to the slide 30, its magnetic field being influenced by a soft magnetic core 32 made of electrical steel or an iron-silicon alloy. The soft magnetic core 32 is arranged on a side of the circuit carrier 21 facing away from the magnetic field sensor 20, so that the magnetic field sensor 20 is located between the bar magnet 31 and the soft magnetic core 32. Since the soft magnetic core 32 is located relative to the magnetic field sensor 20, the magnetic field of the sensor 20 is not affected by the magnetic field of the sensor 20.Since the circuit carrier 21 is stationary and influences the magnetic field of the bar magnet 31, the magnetic field emanating from the bar magnet 31 is not merely shifted by the movement of the slider 30, but is changed by the movement of the slider 30 due to the influence of the soft magnetic core 32.

[0036] The magnetic field sensor 20 is arranged concentrically to the soft magnetic core 32 and concentrically in the second half 15 of the path from starting point 11 to endpoint 12 along the actuation path 10. Thus, the path, which begins at starting point 11 and ends at endpoint 12 and corresponds to the maximum displacement of the slide 30, is divided at a midpoint 13 into a first or front half 14 and a second or rear half 15.

[0037] Assuming that the path from starting point 11 to endpoint 12 along the actuation path 10 has a length L1, the first half 14 and the second half 15 each have a length L2 corresponding to half the length L1. It has proven advantageous if the bar magnet has a length L3 equal to the length L1 of the path from starting point 11 to endpoint 12. Furthermore, it is advantageous if the soft magnetic core 32 completely covers the second half 15 of the path from starting point 11 to endpoint 12 and thus has a length L2 equal to half the length L1.

[0038] To prevent the bar magnet 31 from oscillating or vibrating in a way that alters the magnetic field detectable by the magnetic field sensor 20 when vibrating relative to the magnetic field sensor 20 and thus also to the circuit carrier 21 and the soft magnetic core 32, a guide body 34 can be provided if necessary, which can maintain the distance of the slide 30 orthogonal to the circuit carrier 21 directly or indirectly via corresponding sliding bodies.

[0039] Since the field lines emanating from the south pole S and the north pole N of the bar magnet 31 preferentially pass through or are influenced by the soft magnetic body 32, the field strength measurable by the magnetic field sensor 20, which depends on the displacement of the slider 30 along the actuation path 10, is as shown in Figure 2. Section a) of Figure 2 shows an exemplary position of the bar magnet 31 along the actuation path 10, in which the bar magnet 31, or rather the end face of the bar magnet 31 forming the north pole N, is displaced from the starting point 11 to the area of ​​the center point 13.

[0040] If the field strength or magnetic field 40 is measured by the magnetic field sensor 20 over the entire displacement of the slider 30 or the end face of the bar magnet 31 forming the north pole N from starting point 11 to end point 12, the field line density or flux density or field strength between the bar magnet 31 and the soft magnetic core 32 is shown in section b) of Figure 2. The field strength y is thus given over the path length x along the actuation path 10, where the path length from starting point 11 to end point 12 corresponds to 4.5 mm for example.

[0041] As can be seen directly from section b) of Figure 2, a first extremum or minimum 41 occurs at the starting point 11 and a second extremum or maximum 42 of the course 40 occurs at the end point 12, the course 40 being essentially linear between these extremums 41 , 42.

[0042] If the slider 30 is moved along the actuation path 10, for example by means of a merely indicated actuating element 33, the bar magnet 31 moves relative to the magnetic field sensor 20 and to the soft magnetic core 32, so that the magnetic field sensor 20 outputs a signal 43 or an output voltage V. ou t is generated according to the field strength measured by the magnetic field sensor 20 or according to the curve 40, as shown in section c) of Figure 2.

[0043] * * * * *

Claims

Patent claims 1. Control circuit (1) for linear speed control of an electrically operated hand tool, comprising a magnetic field sensor (20) for detecting a magnetic field and a slider (30) displaceable from a starting point (11) to an end point (12) along a linear actuation path (10) relative to the magnetic field sensor (20), wherein the magnetic field sensor (20) is arranged along the actuation path (10) and a bar magnet (31) is fixed to the slider (30) parallel to the actuation path (10),wherein a soft magnetic core (32) is arranged on a side of the magnetic field sensor (20) facing away from the bar magnet (31) and a magnetic field formed between the bar magnet (31) and the soft magnetic core (32) can be linearly detected by the magnetic field sensor (20) for speed control when the slider (30) moves from the starting point (11) to the end point (12) and can be output by the magnetic field sensor (20) as a linearly changing output signal (43).

2. Control circuit according to claim 1, wherein the soft magnetic Kem (32) is stationary relative to the magnetic field sensor (20).

3. Control circuit according to claim 1 or 2, wherein the soft magnetic core (32) extends along the actuation path (10) and parallel to it and / or wherein the soft magnetic core (32) has a length extension (L2) along the actuation path (10) equal to half a path length (L1) from start point (11) to end point (12) along the actuation path (10) and / or wherein the actuation path (10) from the start point (11) to the end point (12) has a first half (14) and a subsequent second half (15) and the soft magnetic core (32) and / or the magnetic field sensor (20) is arranged in the second half (15) and preferably centrally in the second half (15).

4. Control circuit according to one of the preceding claims, further comprising a parallel path of actuation. (10) extending circuit carrier (21) wherein the magnetic field sensor (20) and / or the soft magnetic Kem (32) are arranged and fixed on the circuit carrier (21) or wherein the magnetic field sensor (20) and the soft magnetic Kem (32) are arranged and fixed on two opposite sides of the circuit carrier (21).

5. Control circuit according to the preceding claim, wherein contact surfaces corresponding to the magnetic field sensor (20) and / or the soft magnetic core (32) are formed on the circuit carrier (21), and wherein the magnetic field sensor (20) and / or the soft magnetic core (32) are designed as surface-mountable components and are fixed to the circuit carrier (21) via the contact surfaces.

6. Control circuit according to one of the preceding claims, wherein the magnetic field sensor (20) is a Hall sensor and / or a linear Hall sensor.

7. Control circuit according to one of the preceding claims, wherein the soft magnetic core (32) is shaped in a plate-like and / or rod-like form and / or wherein the soft magnetic core (32) is formed from at least one electrical steel sheet and / or wherein the soft magnetic core (32) is formed from an iron-silicon alloy.

8. Control circuit according to one of the preceding claims, wherein the bar magnet (31 ) has a length extension (L3) which corresponds to or is greater than the path length (L1 ) from start point (11 ) to end point (12 ).

9. Control circuit according to one of the preceding claims, wherein the magnetic field sensor (20) is configured to output a voltage (Vout) as an output signal (43), which changes linearly depending on the distance traveled when the slider (30) moves from the starting point (11) to the end point (12).

10. Control circuit according to one of the preceding claims, wherein the slide (30) is spring-returned to the starting point (11) and / or kinematically connected to an actuating element (33) that can be operated by an operator.

11. Control circuit according to one of the preceding claims, wherein at least one guide body (34) is provided on the slider (30) which is held without contact with the magnetic field sensor (20) and by which a distance of the bar magnet (31) to the magnetic field sensor (20) and / or the soft magnetic core (32) is maintained that is orthogonal to the actuation path (10).

12. Electrically operated hand tool comprising an electric motor and a control circuit (1) according to one of the preceding claims, wherein the electric motor is controlled by the output signal (43) of the magnetic field sensor (20).

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