Control circuit for controlling the speed of an electrically operated hand tool

Abstract

The invention relates to a control circuit (1) for controlling the speed of an electrically operated hand tool, the control circuit comprising: a first contact track (10) which extends without interruption from a starting point (11) to an end point (12) and is connected to a circuit output (53); a second contact track (20) which extends parallel to the first contact track (10) and is formed from a plurality of contact surfaces (21, 22, 23) that are arranged one behind the other in a row and are insulated from one another, with a ground connection (GND) applied to a first contact surface (21) of the row and a supply voltage (VCC) applied to a last contact surface (23) of the row; and a pick-up (30) which can be moved between the starting point (11) and the end point (12) and which has at least one first contact (31) and at least one second contact (32) that electrically connect the first contact track (10) to the second contact track (20); and further comprising a plurality of resistors (41, 42, 43) which are connected in series, the resistors (41, 42, 43) each being connected to a contact surface (11, 12, 13) of the second contact track (20) such that the voltage present at the circuit output (53) can be varied stepwise between ground (GND) and supply voltage (VCC) by a movement of the pick-up (30) without physical contact with the resistors (41, 42, 43).

Description

[0001] Control circuit for speed control on an electrically operated hand tool

[0002] Description:

[0003] The invention relates to a control circuit for speed control on an electrically operated hand tool.

[0004] A wide variety of control circuits for electrically powered hand tools are known from the state of the art. These are often based on a sliding contact being moved directly along a resistance track, which has several disadvantages.

[0005] On the one hand, the direct contact with the resistance track leads to material removal or wear on the resistance track over time, so that the output voltage that can be generated by the control circuit changes over time and failures can occur. Furthermore, the sliding contact is held on the resistance track by a spring. This spring must be strong enough to ensure good electrical contact, but on the other hand it must be as weak as possible to minimize the mechanical force on the resistance track and thus wear. However, at certain frequencies and vibrations of the hand tool, this can lead to the sliding contact briefly losing contact with the resistance track and therefore no clean output voltage or control voltage can be generated.

[0006] The invention is therefore based on the object of overcoming the aforementioned disadvantages and of providing a control circuit for speed control on an electrically operated hand tool, with which a continuously variable control or output voltage can be generated with a long service life.

[0007] This problem is solved by the combination of features according to patent claim 1.

[0008] According to the invention, a control circuit for speed control on an electrically operated hand tool is therefore proposed. For example, a control voltage or control signal for controlling an electric motor of the hand tool can be generated by the control circuit or at the circuit output of the control circuit. The control circuit proposed here has a first contact track and a second contact track. The first contact track extends continuously from a starting point to an end point and is connected to a circuit output. The second contact track extends parallel to the first contact track, with the contact tracks preferably being of equal length.However, the second contact track is not continuous, but rather is formed from a plurality of contact surfaces arranged one after the other in a row and insulated from one another, of which ground is applied to a first contact surface in the row and a supply voltage is applied to a last contact surface in the row. Furthermore, the invention provides that the control circuit further comprises a pickup movable between a starting point and an end point, having at least one first contact for contacting the first contact track and at least one second contact for contacting the second contact track, so that the first contact track is electrically connected to the second contact track by the pickup.It is advantageous that a plurality of series-connected resistors is also provided, wherein a tap is provided on a first resistor in the series and a last resistor in the series, as well as between every two resistors, and each tap is connected to a contact surface of the second contact track, so that the voltage applied to the circuit output can be varied stepwise between ground and supply voltage by moving the tap. Since the at least one second contact of the tap is not moving on the resistors or on a resistance track explained below, the tap is not in direct physical contact with the resistors, so that no physical wear occurs on the resistors due to the tap.

[0009] A variant in which the consumer has a plurality of first contacts and a plurality of second contacts is also advantageous.

[0010] Furthermore, in such a variant, it can advantageously be provided that the first contacts and the second contacts are each independently spring-loaded, contact the respective contact track independently of one another, and have mutually parallel sliding paths on the respective contact track. Accordingly, each first contact on the first contact track defines a respective sliding path, and each second contact on the second contact track defines a respective sliding path. Because the first and second contacts do not directly touch a resistance track, it cannot be worn away and is therefore not subject to mechanical wear.Furthermore, there is not just one spring-loaded contact per contact track, but the contacts are spring-loaded independently of each other, so that in the event of vibrations it is extremely unlikely that all first contacts and all second contacts will lose electrical contact with the respective contact track, so that a continuous output signal or control signal can be generated.

[0011] A further development according to the invention also provides that the second contacts are designed in such a way that when the pickup moves from the starting point to the end point, at least one second contact is always in contact with at least one of the contact surfaces, so that an uninterrupted control signal is generated at the output signal.

[0012] Furthermore, it can be provided that the second contacts are designed in such a way that when the pickup moves from the starting point to the end point, all second contacts are always in contact with the same contact surface or with the same contact surfaces.

[0013] It can also be provided that each of the second contacts initially touches one contact surface alone when the pickup moves and then additionally touches another contact surface, so that when there is a transition between two contact surfaces, two contact surfaces are briefly in contact.

[0014] Both the first contact track and the second contact track can be made of an electrically conductive, abrasion-resistant material. The first contact track and / or the second contact track can be gold-plated for this purpose, for example. An advantageous development provides that the first contacts are each spring-loaded by a first spring, and wherein the first springs have different resonant frequencies and / or spring constants from one another. Alternatively or additionally, the second contacts are preferably each spring-loaded by a second spring, and wherein the second springs have different resonant frequencies and / or spring constants from one another.

[0015] Although in principle a wide variety of springs can be used, it has proven advantageous to provide the contacts as contact areas formed on spring arms, whereby the spring arms can have different resonance frequencies or spring constants, for example due to different lengths, bending radii or contours.

[0016] Furthermore, the first contacts can be offset from one another in the longitudinal direction of the first contact track, and the second contacts can be offset from one another in the longitudinal direction of the second contact track. Regardless of the fact that such an offset can result from different springs, it is advantageous that the contacts are further apart from one another and thus less susceptible to contamination.

[0017] The contact surfaces, and in particular the contact surfaces located between the first contact surface and the last contact surface of the row, can also be designed in a parallelogram or diamond shape, which on the one hand allows an uninterrupted output signal to be generated and on the other hand makes the contact path less susceptible to errors due to contamination.

[0018] The series-connected resistors can also be designed, in particular, as a preferably continuous resistor path, along which the taps are provided at regular, particularly uniform, intervals. This has the advantage that discrete resistors, for example, SMD components, can be completely dispensed with, and the resistor path can be formed directly with the circuit, for example, by printing it onto a carrier element, thus completely eliminating the need for complex assembly.

[0019] The resistors connected in series can be covered or encapsulated, for example, by a foil or varnish.

[0020] Additionally or alternatively, it can be provided that the second contact track is preferably formed together with the first contact track on a first side of a first carrier element and the series-connected resistors or the contact track are arranged on an opposite second side of the first carrier element, ie on the back of the same carrier element or on a second carrier element different therefrom, wherein the two carrier elements can preferably be spaced apart and / or structurally separated from one another.

[0021] Furthermore, it can also be provided that the resistors connected in series or the resistance track are structurally separated from the second contact track and preferably also from the first contact track.

[0022] For this purpose, a shading element and, for example, a plastic bar extending parallel to the second contact track can be provided between the resistors or the resistance track and the contact track to prevent the distribution of contamination accumulating on the contact tracks to the resistors or the resistance track. Overall, the resistance track can be designed cost-effectively, as friction-reducing additives or coatings on the resistance track are unnecessary, as the contacts do not rub against it.

[0023] Since the resistance track does not have to be formed directly on the contacts, it can be formed "anywhere" to save space, i.e., at a distance from the pickup. For example, it is possible to save space by forming the resistance track on the back of a carrier element, on the front of which the contact tracks against which the pickup rubs are arranged.

[0024] Another advantage is that the resistance track is adjusted to a predetermined path or corrected to a linear path by so-called trimming. Trimming can preferably be performed by laser, which is not possible with a resistance track that also serves as a sliding or contact track. In particular, trimming can reduce the tolerances of the resistance track. This is particularly advantageous for more precise control of the electronics or motor of the hand tool, or for a more accurate output signal at the circuit output.

[0025] The features disclosed above can be combined as desired, as long as this is technically possible and they do not contradict each other.

[0026] 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 figure. It shows:

[0027] Fig. 1 shows a control circuit. The figure is schematic by way of example and shows a control circuit 1 divided between two carrier elements 51, 52, which can also be referred to as printed circuit boards or circuit boards. The control circuit 1 has a GND connection 54 for contacting ground (GND) and a VCC connection 55 for contacting a supply voltage (VCC), as well as a circuit output 53, at which a control or output signal generated by the control circuit 1 is applied, which can be varied stepwise between 0V corresponding to ground and the supply voltage, as shown by the stepped voltage curve 61.

[0028] Basically, the control circuit 1 on the first carrier element 51 has a first contact track 10 and a second contact track 20, which are arranged parallel to one another and extend over the same length. The first contact track 10 extends continuously from a starting point 11 to an end point 12 and is connected to the circuit output 53, at which, as described, the control signal for controlling the electrically operated hand tool can be output. In contrast, the second contact track 20 is not continuous, but is formed by or from a plurality of contact surfaces 21, 22, 23 arranged one after the other in a row and insulated from one another, wherein each contact surface 21, 22, 23 serves to generate a control voltage step.In the present case, eight contact surfaces 22 are provided between the first contact surface 21 and the last contact surface 23, so that a total of 10 control stages are possible, of which the first corresponds to 0V and the last to VCC.

[0029] In this case, on a second support element 52 and thus structurally separate, a resistance track 40 is further provided, which, through the individual taps 44, essentially corresponds to a plurality of series-connected resistors 41, 42, 43. The resistance track 40 is a continuous resistance track, the resistance of which, changing along its course, leads to a linear voltage buildup, as shown by the continuous voltage curve 60.

[0030] The first resistor 41 is connected to the first contact pad 21 and to ground GND via a tap 44. The last resistor 43 is connected to the last contact pad 23 and to the supply voltage VCC via a tap 44.

[0031] The taps 44 located between two resistors 41, 42, 43 are each contacted with a contact surface 22.

[0032] The contacting of the taps 44 with the contact surfaces 21, 22, 23 is realized via lines 50, so that the support elements 51, 52 are structurally separated and, for example, the second support element 52 can be housed independently of the first support element 51 and can be protected accordingly from contamination.

[0033] If the two carrier elements 51, 52 are to be understood as the front side 51 and the back side 52 of a single carrier element in an alternative embodiment, the lines 50 can also be formed directly on this by corresponding conductor tracks.

[0034] Furthermore, a pickup 30 is provided which is movable between the starting point 11 and the end point 12 and has, in this case, two first contacts 31 and, in this case, two second contacts 32, by means of which the first contact track 10 is electrically connected to the second contact track 20. The first contacts 31 each contact the first contact track 10 independently of one another, and the second contacts 32 each contact the second contact track 20 independently of one another, wherein the contacts 31, 32 on the respective contact track 10, 20 have or determine mutually parallel, ie likewise independent, sliding paths. For the resilient contact of the contacts 31, 32 on the respective contact track 10, 20, a spring 33, 34 is each assigned to each of them, wherein the contacts 31, 32 are formed integrally with their respective spring 33, 34 as a spring arm.Because a plurality of first contacts 31 are pressed by a spring 33 onto the first contact track 10 and a plurality of second contacts 32 are pressed by a spring 34 onto the second contact track 20, it is unlikely that all first contacts 31 or all second contacts 32 will simultaneously lose their electrical contact with their respective contact track 10, 20, so that a continuous output signal can be provided at the circuit output 53.

[0035] In addition, since the second contacts 32 are not moved directly on the resistance track 40, there is no mechanical wear on it, which significantly increases the service life and allows the use of inexpensive materials for the resistance track 40.

[0036] * * * * *

Claims

Patent claims 1. A control circuit (1) for speed control on an electrically operated hand tool, comprising a first contact track (10) extending continuously from a starting point (11) to an end point (12) and connected to a circuit output (53), a second contact track (20) extending parallel to the first contact track (10) and formed from a plurality of contact surfaces (21, 22, 23) arranged one after the other in a row and insulated from one another, of which ground (GND) is applied to a first contact surface (21) of the row and a supply voltage (VCC) is applied to a last contact surface (23) of the row, and comprising a pickup (30) movable between the starting point (11) and the end point (12), which pickup has at least one first contact (31) for contacting the first contact track (10) and at least one second contact (32) for contacting the second contact track (20),by which the first contact track (10) is electrically connected to the second contact track (20), further comprising a plurality of resistors (41, 42, 43) connected in series, wherein a tap (44) is provided on a first resistor (41) of the series and a last resistor (43) of the series as well as between each two resistors (41, 42, 43), and each tap (44) is connected to a respective contact surface (11, 12, 13) of the second contact track (20), so that the voltage applied to the circuit output (53) can be varied stepwise between ground (GND) and supply voltage (VCC) by a movement of the tap (30) without physical contact with the resistors (41, 42, 43).

2. Control circuit according to claim 1, wherein the pickup (30) has a plurality of first contacts (31) and a plurality of second contacts (32).

3. Control circuit according to claim 2, wherein the first contacts (31) and the second contacts (32) are each spring-loaded independently of one another, contact the respective contact track (10, 20) independently of one another and have mutually parallel sliding paths on the respective contact track (10, 20).

4. Control circuit according to one of the preceding claims 2 or 3, wherein the second contacts (32) are designed such that when the pickup (30) moves from the starting point (11) to the end point (12), at least one second contact (32) is always in contact with at least one of the contact surfaces (21, 22, 23).

5. Control circuit according to one of the preceding claims 2 to 4, wherein the second contacts (32) are designed such that when the pickup (30) moves from the starting point (11) to the end point (12), all second contacts (32) are always in contact with the same contact surface (21, 22, 23) or with the same contact surfaces (21, 22, 23).

6. Control circuit according to one of the preceding claims 2 to 5, wherein the first contacts (31) are each sprung by a first spring (33) and wherein the first springs (33) have mutually different resonant frequencies and / or spring constants and / or wherein the second contacts (32) are each sprung by a second spring (34) and wherein the second springs (34) have mutually different resonant frequencies and / or spring constants.

7. Control circuit according to one of the preceding claims 2 to 6, wherein the first contacts (31) are offset from one another in the longitudinal direction of the first contact track (10) and / or wherein the second contacts (32) are offset from one another in the longitudinal direction of the second contact track (20).

8. Control circuit according to one of the preceding claims, wherein the contact surfaces (21, 22, 23) are parallelogram-shaped or diamond-shaped.

9. Control circuit according to one of the preceding claims, wherein the series-connected resistors (41, 42, 43) are encapsulated and / or wherein the second contact track (20) is formed on a first side of a first carrier element (51) and the series-connected resistors (41, 42, 43) are arranged on an opposite second side of the first carrier element (51) or on a second carrier element (52) and / or wherein the series-connected resistors (41, 42, 43) are structurally separated from the second contact track (20).

10. Control circuit according to one of the preceding claims, wherein the series-connected resistors (41, 42, 43) are designed as a resistance track (40) on which the taps (44) are provided at regular intervals. * * * * *

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