Control circuit for the linear speed control of an electrically operated 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 comprising a slider (30) which can be displaced relative to the magnetic field sensor (20) along a linear actuation path (10) from a starting point (11) to an end point (12), wherein the magnetic field sensor (20) is positioned along the actuation path (10), and two axially magnetised bar magnets (31, 32), that are arranged antiparallel to one another, are fixed to the slider (30) on opposite sides of the magnetic field sensors (20), wherein the bar magnets (31, 32) can be moved, together with the slider (30), along the actuation path (10) on both sides of the magnetic field sensor (20), and a magnetic field generated between the bar magnets (31, 32) can be linearly detected by the magnetic field sensor (10) during movement of the slider (30) from the starting point (11) to the end point (12) for speed control, and can be output by the magnetic field sensor (20) as a linearly varying output signal (43).

Description

[0001] Control circuit for linear speed control of an electrically operated hand tool and hand tool with such a control circuit

[0002] Description:

[0003] The invention relates to a control circuit for linear speed control of an electrically operated hand tool and hand tool with such a control circuit.

[0004] A large number of electrically operated hand tools are known from the state of the art, which often have an electric motor, the speed of which is to be controlled by an operator.

[0005] For more intuitive operation, it is usually intended that the speed of the electric motor be linearly variable or that the hand tool be linearly controlled. Basically, two variants are common. The first of these provides a circuit based on electrical contact, in which a wiper, touching contacts and, in particular, a resistance strip, can be moved across a circuit board. However, due to the direct contact, this leads to high mechanical wear, and the mechanical contact is also susceptible to vibrations, so that wipers sometimes cannot generate a continuous output signal, at least under certain vibration conditions.

[0006] Another known alternative is to move a magnet 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. However, this approach is somewhat problematic because the magnetic field generated by a single magnet is approximately linear only within a very limited range, so the actuation travel—in which a linearly changing magnetic field can be detected by the magnetic field sensor—is very short. If the actuation travel extends beyond this limited range, the essentially sinusoidal output signal of the magnetic field sensor must be converted into a linear signal using additional electronics, which is correspondingly complex and expensive.

[0007] The invention is therefore based on the object of overcoming the aforementioned disadvantages and of providing a control circuit for linear speed control of a hand tool or a hand tool with such a control circuit, by means of which the hand tool can be controlled linearly in a simple and cost-effective manner and with little or no wear along a comparatively long actuating path.

[0008] This object is achieved by the combination of features according to patent claim 1. According to the invention, a control circuit is therefore proposed, in particular 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 has a magnetic field sensor for detecting a magnetic field and a slider displaceable from a starting point to an end point along a linear actuation path relative to the magnetic field sensor, wherein the magnetic field sensor is arranged along the actuation path and one, i.e. two, anti-parallel arranged axially magnetized bar magnets are fixed to the slider on opposite sides of the magnetic field sensor.The bar magnets - hereinafter also simply referred to as magnets - are therefore preferably arranged directly opposite one another with regard to the actuation path, i.e. at the same height, whereby a south pole of the first bar magnet is opposite a north pole of the second bar magnet due to the anti-parallel arrangement with regard to the actuation path, and vice versa. This results in most of the field lines between the two magnets running from one pole of one magnet to the corresponding opposite pole of the second magnet. This increases the field line density in the space directly above and below the magnets, whereas in the space between them and at a greater distance the field line density decreases considerably. For the area between the magnets the field line density orFlux density is therefore maximum in the area of ​​the poles (south pole / north pole) of the magnets and changes linearly from one extreme (e.g. at the starting point) to the other extreme (e.g. at the end point) in particular along the actuation path centered between the magnets. Together with the slider to which the magnets are fixed, the bar magnets can be moved along the actuation path on both sides of the magnetic field sensor, so that a magnetic field formed between the bar magnets changes essentially linearly along the actuation path and can be linearly detected by the magnetic field sensor when the slider moves from the starting point to the end point for speed control or its change and can be output by the magnetic field sensor as an output signal that changes linearly along the actuation path.

[0009] An advantageous development of the control circuit provides that the magnetic field sensor outputs an output voltage as an output signal and the output voltage changes linearly with a uniform movement of the slider from the starting point to the end point or the change in the output voltage from the starting point to the end point is linear along the actuation path.

[0010] Preferably, the bar magnets have an identical longitudinal extension parallel to the actuation path and are further preferably point-symmetrical to one another with respect to a mirror point lying on the actuation path, so that the actuation path is centered between the antiparallel arranged bar magnets and parallel to them.

[0011] The longitudinal extension of the bar magnets can also correspond to a path length from the starting point to the end point along the actuation path. Alternatively, the longitudinal extension of the bar magnets can also be greater than the path length, for example, between 1% and 10% or 10% and 20% greater than the path length. The bar magnets can also be centered to the path length or positioned at a midpoint between the starting point and the end point, so that the characteristic curve also has a linear profile at the starting point and the end point, or in the area between the starting point and the end point, and does not transition into a parabolic profile at the starting point and the end point. This also compensates for manufacturing tolerances that would otherwise make the characteristic curve between the starting point and the end point non-linear or nearly linear. Furthermore, the slide is preferably spring-returned to the starting point and / or kinematically connected to an actuating element that can be actuated by an operator.

[0012] The magnetic field sensor is preferably a Hall sensor and in particular a linear Hall sensor.

[0013] The control circuit can also further comprise a circuit carrier arranged parallel to the actuation path, on which the magnetic field sensor is arranged and from which the magnetic field sensor extends onto or into the actuation path. As a result, the slide can be designed essentially fork-shaped, with one magnet arranged on each fork prong or web.

[0014] Alternatively, the control circuit can also have a sensor holder arranged coaxially to the actuation path, to which the magnetic field sensor is fixed and from which the magnetic field sensor can extend onto the actuation path, which has the advantage that the slider can be designed essentially tubularly, which prevents oscillation or relative movement of the magnets to one another or of the slider in the region of the magnets.

[0015] In particular, in the first variant, it can therefore be provided that the slide has at least one web or bridge that encompasses the magnetic field sensor over the actuation path to stabilize the bar magnets, thus preventing any relative movement of the magnets to one another or maintaining their relative position. At least one such web or bridge is preferably provided at the poles of the magnets and / or at a transition between the poles of the magnets. Furthermore, such a web or bridge can also extend along the actuation path over the entire longitudinal extent of the magnets and enclose the magnetic field sensor on one side.

[0016] In order to prevent a movement of the magnetic field sensor relative to the magnets that is orthogonal to the actuation path, it can further be provided that two guide bodies are provided on the slide on opposite sides of the magnetic field sensor, which guide bodies are held contact-free with the magnetic field sensor and by means of which a distance of the magnetic field sensor to the bar magnets that is orthogonal to the actuation path is maintained. During a normal movement of the slide along the actuation path, the guide bodies do not touch the magnetic field sensor. If vibrations or other movements occur that cause the distance of the magnetic field sensor to fluctuate orthogonally to the actuation path and a measurement result of the magnetic field sensor would thereby be falsified, the guide bodies can touch the magnetic field sensor or counter-bodies formed around it, so that the orthogonal distance does not change or changes only minimally.changed within a previously known tolerance range.

[0017] A further aspect of the invention relates to an electrically operated hand tool with an electric motor and a control circuit proposed according to the invention, wherein the electric motor or its speed is controlled by the output signal of the magnetic field sensor.

[0018] The features disclosed above can be combined as desired, as long as this is technically possible and they do not contradict each other.

[0019] Other advantageous developments of the invention are characterized in the subclaims or are presented in more detail below, together with the description of the preferred embodiment of the invention, with reference to the figures. They show: Fig. 1 shows a control circuit;

[0020] Fig. 2 two bar magnets with a course of a field strength determined between them and an output voltage generated from them serving as an output signal.

[0021] The figures are schematic examples. Identical reference numerals in the figures indicate identical functional and / or structural features.

[0022] Figure 1 shows a basic structure of a control circuit 1 proposed according to the invention. This circuit comprises a magnetic field sensor 20 designed as a linear Hall sensor, which is arranged on a circuit carrier 21 and electrically contacted.

[0023] A slider 30 is provided, which is movable relative to the magnetic field sensor 20 and can be moved linearly along the actuation path 10. A bar magnet 31, 32 is fixed to the slider 30 or to two webs extending from a base body of the slider 30 parallel to the actuation path 10. The bar magnets 31, 32 are aligned antiparallel, so that the bar magnets 31, 32 are opposite one another with opposite poles or pole pairs with respect to the actuation path 10 and have the actuation path 10 and the magnetic field sensor 20 arranged thereon between them.

[0024] The magnetic field sensor 20 is shown here centered on a center point 13, which is located centrally between the starting point 11 and the end point 12 on the actuation path 10. The representation or the illustrated position of the slider 30 shows that the center point 13 also corresponds to a mirror point to which the bar magnets 31, 32 are arranged point-symmetrically.

[0025] In order to prevent the bar magnets 31, 32 from oscillating relative to one another during vibration and thus from changing the magnetic field formed between them, a bridge or web 34 is indicated here, which spans the actuating path 10 and stabilizes the slide 30 in the area of ​​the bar magnets 31, 32.

[0026] Since a south pole S of the first bar magnet 31 is opposite a north pole N of the second bar magnet 32 ​​due to the anti-parallel arrangement with respect to the actuating path 10 and vice versa, and a north pole N of the first bar magnet 31 is opposite a south pole S of the second bar magnet 32 ​​due to the anti-parallel arrangement with respect to the actuating path 10, it follows that most of the field lines between the two magnets 31, 32 run from one pole of one magnet 31, 32 to the corresponding opposite pole of the second magnet 31, 32. This results in extreme points for the course 40 of the field line density or flux density or field strength between the bar magnets 31, 32, i.e. in the region of the poles, for example a first extreme point 41 at the south pole S of the second magnet 32 ​​and a second extreme point 42 at the south pole S of the first magnet 31, as shown in Figure 2, wherein the course 40 changes essentially linearly between the extreme points 41, 42.

[0027] If the slider 30 is now moved along the actuating path 10, for example by means of an only indicated actuating element 33, the bar magnets 31, 32 move relative to the magnetic field sensor 20, which generates an output 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 the illustration in Figure 2.

[0028] * * * * *

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 comprising a slider (30) which is 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 two antiparallel arranged axially magnetized bar magnets (31, 32) are fixed to the slider (30) on opposite sides of the magnetic field sensor (20), wherein the bar magnets (31, 32) are movable with the slider (30) along the actuation path (10) on both sides of the magnetic field sensor (20) and a between the bar magnets (31,32) is linearly detectable by the magnetic field sensor (10) during a movement of the slider (30) from the starting point (11) to the end point (12) for speed control 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 magnetic field sensor (20) outputs an output voltage (Vout) as an output signal (43) and the output voltage (Vout) changes linearly upon movement of the slider (30) from the starting point (11) to the end point (12).

3. Control circuit according to claim 1 or 2, wherein the bar magnets (31, 32) have an identical Longitudinal extension (L) parallel to the actuating path (10).

4. Control circuit according to the preceding claim, wherein the longitudinal extent (L) of the bar magnets corresponds to a path length from the starting point (11) to the end point (12) along the actuating path (10) or is greater than the path length.

5. Control circuit according to one of the preceding claims, wherein the slider (30) is spring-returned to the starting point (11) and / or is kinematically connected to an actuating element (33) operable by an operator.

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, further comprising a circuit carrier (21) arranged parallel to the actuating path (10), on which circuit carrier the magnetic field sensor (20) is arranged and from which the magnetic field sensor (20) extends onto the actuating path (10), or comprising a sensor holder arranged coaxially to the actuating path (10), to which sensor holder the magnetic field sensor (20) is fixed and from which the magnetic field sensor (20) extends onto the actuating path (10).

8. Control circuit according to one of the preceding claims, wherein the slide (30) has at least one web (34) encompassing the magnetic field sensor (20) over the actuating path (10) for stabilizing the bar magnets (31, 32).

9. Control circuit according to one of the preceding claims, wherein on the slide (30) on opposite sides of the The magnetic field sensor (20) has two guide bodies held in contact with the magnetic field sensor, by means of which a distance between the magnetic field sensor (20) and the bar magnets (31, 32) is maintained that is orthogonal to the actuation path (10).

10. An electrically operated hand tool with 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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