Control circuit for speed control of an electric hand-held tool

Abstract

The present invention relates to a control circuit (1) for speed control of an electric handheld tool, having a first contact rail (10) that extends continuously from a starting point (11) to an ending point (12) and is connected to a circuit output terminal (53), a second contact rail (20) that extends parallel to the first contact rail (10) and is formed by a plurality of sequentially arranged and mutually insulated contact surfaces (21, 22, 23), wherein a ground potential (GND) is applied at the first contact surface (21) of the arrangement, a power supply voltage (VCC) is applied at the last contact surface (23) of the arrangement, and having a sliding contact that can move between the starting point (11) and the ending point (12). (30) The sliding contact has at least one first contact (31) and at least one second contact (32). The first contact rail (10) is electrically connected to the second contact rail (20) through the sliding contact. It also has a plurality of resistors (41, 42, 43) connected in series, wherein these resistors (41, 42, 43) are respectively connected to a contact surface (11, 12, 13) of the second contact rail (20), so that the voltage applied to the circuit output terminal (53) can be graded between ground potential (GND) and power supply voltage (VCC) by moving the sliding contact (30). The sliding contact has no physical contact with the resistors (41, 42, 43).

Description

[0001] manual

[0002] This invention relates to a control circuit for speed control of electric handheld tools.

[0003] Various control circuits for electric hand tools are known in the prior art. These circuits are typically based on the direct movement of a sliding contact on a resistive track, which has several drawbacks.

[0004] On the one hand, due to direct contact with the resistor rails, the material on the resistor rails will wear or be depleted over time, causing the output voltage that the control circuit can generate to change over time, which may lead to malfunction.

[0005] Furthermore, the sliding contact is elastically held on the resistor track, where the elasticity should be strong enough to ensure good electrical contact, but as weak as possible to minimize the mechanical forces acting on the resistor track and the corresponding wear. However, under certain frequencies and handheld tool vibrations, this may cause the sliding contact to temporarily lose contact with the resistor track, thus preventing the generation of a clean output voltage or control voltage.

[0006] Therefore, the object of the present invention is to overcome the aforementioned disadvantages and to provide a control circuit for speed control of electric hand tools, which can generate a continuously variable control voltage or output voltage with a long lifespan.

[0007] This task is solved by the combination of features described in claim 1 of the patent.

[0008] Therefore, a control circuit for speed control of an electric hand-held tool is proposed according to the present invention. For example, a control voltage or control signal for controlling the motor of the hand-held tool can be generated by this control circuit or at the circuit output terminal of the control circuit. The control circuit proposed herein has a first contact rail and a second contact rail. The first contact rail extends continuously from a starting point to an ending point and is connected to the circuit output terminal. The second contact rail extends parallel to the first contact rail, wherein the contact rails are preferably of equal length. However, the second contact rail is not continuous, but is formed by a plurality of sequentially arranged and mutually insulated contact surfaces, wherein a ground potential is applied at the first contact surface of the arrangement and a power supply voltage is applied at the last contact surface of the arrangement. Furthermore, according to the present invention, the control circuit also has a sliding contact movable between the starting point and the ending point, having at least one first contact for contacting the first contact rail and at least one second contact for contacting the second contact rail, such that the first contact rail is electrically connected to the second contact rail via the sliding contact. Advantageously, multiple resistors are also provided in series, with a tap at the first and last resistors in series and between every two resistors, and each tap is connected to a contact surface of a second contact rail, such that the voltage applied to the circuit output can be graded between ground potential and power supply voltage by moving the slider. Since at least one of the second contacts of the slider does not move directly on the resistor or the resistor rail as described further below, the slider does not have direct physical contact with the resistor, thus preventing physical wear on the resistor due to the slider.

[0009] In addition, a variation is also advantageous in which the sliding contact has multiple first contacts and multiple second contacts.

[0010] In this variation, it can also be advantageously stipulated that the first contact and the second contact are independently elastically supported, independently contact their respective contact tracks, and have parallel sliding paths on their respective contact tracks. Accordingly, each first contact defines its own sliding path on the first contact track, and each second contact defines its own sliding path on the second contact track.

[0011] Since the first and second contacts do not slide directly on the resistance rails, the resistance rails will not wear out, and consequently, will not be subject to wear. Furthermore, not only is there an elastic contact for each contact rail, but these contacts are also independently elastically supported. Therefore, in the event of vibration, the probability that all first and second contacts simultaneously lose electrical contact with their respective contact rails is extremely low, thus enabling the generation of continuous output or control signals.

[0012] A further improvement according to the invention further specifies that the second contact is designed such that at least one second contact remains in contact with at least one contact surface during the movement of the sliding contact from the starting point to the ending point, thereby generating an uninterrupted control signal at the output signal.

[0013] Furthermore, it can be specified that the second contacts are designed such that all second contacts remain in contact with the same contact surface or the same contact surface during the process of the sliding contact moving from the starting point to the ending point.

[0014] Alternatively, it can be stipulated that during the movement of the sliding contact, each second contact first contacts one contact surface individually, and then additionally contacts another contact surface, thus briefly contacting both contact surfaces during the transition between the two contact surfaces.

[0015] Both the first and second contact tracks can be made of conductive, wear-resistant materials. For this purpose, the first and / or second contact tracks can, for example, be gold-plated.

[0016] An advantageous further improvement specifies that the first contacts are each elastically supported by a first spring, and the first springs have different resonant frequencies and / or spring constants relative to each other. Similarly, alternatively or additionally, it is specified that the second contacts are preferably elastically supported by second springs, and the second springs have different resonant frequencies and / or spring constants relative to each other.

[0017] Although various different springs can be used in principle, it has proven advantageous to set the contact point as a contact area formed on the spring arm, wherein the spring arm can have different resonant frequencies or spring constants, for example, by varying lengths, bending radii, or profiles.

[0018] Furthermore, the first contacts can be staggered from each other in the longitudinal direction of the first contact track, and similarly, the second contacts can be staggered from each other in the longitudinal direction of the second contact track. Aside from the possibility that this misalignment might be caused by different springs, the advantage is that the greater distance between the contacts makes them less susceptible to contamination.

[0019] The contact surfaces, especially those between the first and last contact surfaces in the arrangement, can also be designed as parallelograms or rhombuses. This allows for uninterrupted output signals and makes the contact track less susceptible to contamination.

[0020] Series-connected resistors can also be preferably formed as continuous resistor tracks with taps spaced at regular, particularly uniform, intervals. The advantage is that discrete resistors, such as SMD components, can be completely eliminated, and the resistor tracks can be formed directly on the carrier element along with the circuitry, for example, by printing, thus completely eliminating complex assembly processes.

[0021] In this case, the series-connected resistors or resistor tracks can be covered or encapsulated, for example, by a thin film or varnish.

[0022] Additionally or alternatively, it may be specified that the second contact rail is preferably formed together with the first contact rail on the first side of the first carrier element, while the series-connected resistor or resistor rail is disposed on the opposite second side, i.e., on the back of the same carrier element, or on a different second carrier element, wherein the two carrier elements are preferably spaced apart and / or structurally separated from each other.

[0023] Furthermore, it can be specified that the series-connected resistors or resistor rails are structurally separated from the second contact rail, and preferably also from the first contact rail. For this purpose, a shielding element, such as a plastic insulating strip extending parallel to the second contact rail, can be provided between the resistors or resistor rails and the contact rails to prevent contaminants falling on the contact rails from distributing onto the resistors or resistor rails.

[0024] Overall, resistance rails can be implemented at low cost because, for example, friction-reducing additives or coatings on the resistance rails can be omitted, since the contacts do not slide on them.

[0025] Since the resistance track does not need to be formed directly on the contact, it can be formed "anywhere," that is, away from the sliding contact, saving space. For example, the following space-saving method is feasible: the resistance track is formed on the back of the carrier element, while a contact track on the front of the element is provided for the sliding contact to slide on.

[0026] Another advantage is that the resistance track can be adjusted to a predetermined curve or corrected to a linear curve through a process called trimming, which is preferably performed by laser, something impossible for resistance tracks that also function as sliding or contact tracks. In particular, trimming can reduce the tolerances of the resistance track. This is advantageous for more precise control of the electronics or motors in handheld tools, or for obtaining more accurate output signals at the circuit output.

[0027] Provided it is technically feasible and not contradictory, the features disclosed above can be combined as needed.

[0028] Other advantageous embodiments of the invention are described in the dependent claims, or are described in more detail below together with the description of preferred embodiments of the invention, with reference to the accompanying drawings.

[0029] Figure 1 The control circuit is shown.

[0030] The accompanying drawing schematically illustrates a control circuit 1 distributed across two carrier elements 51 and 52, which may also be referred to as printed circuit boards or circuit boards. The control circuit 1 has a GND connector 54 for contacting ground potential (GND) and a VCC connector 55 for contacting the power 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. This signal varies in stages between 0V, corresponding to ground potential, and the power supply voltage, as shown by a graded voltage curve 61.

[0031] Basically, the control circuit 1 has a first contact rail 10 and a second contact rail 20 on the first carrier element 51, which are arranged parallel to each other and extend the same length. The first contact rail 10 extends continuously from the start point 11 to the end point 12 and is connected to the circuit output terminal 53, where, as described above, a control signal for controlling the electric handheld tool can be output. In contrast, the second contact rail 20 is not continuous, but is formed by a plurality of sequentially arranged and mutually insulated contact surfaces 21, 22, 23, each of which is used to generate a control voltage level. In this example, eight contact surfaces 22 are provided between the first contact surface 21 and the last contact surface 23, so there can be a total of 10 control levels, where the first level corresponds to 0V and the last level corresponds to VCC.

[0032] In this example, a resistance track 40 is also provided on the second carrier element 52 in a structurally separate manner. This resistance track corresponds substantially to a plurality of series-connected resistors 41, 42, and 43 via various taps 44. The resistance track 40 is a continuous resistance track, and the resistance varying along its path results in a linear voltage buildup, as shown by the continuous voltage curve 60.

[0033] The first resistor 41 is connected to the first contact surface 21 via a tap 44 and is in contact with ground potential GND. The last resistor 43 is connected to the last contact surface 23 via a tap 44 and is in contact with power supply voltage VCC.

[0034] Taps 44 located between every two resistors 41, 42, and 43 are connected to a contact surface 22.

[0035] The contact between tap 44 and contact surfaces 21, 22, 23 is achieved through wire 50, so the carrier elements 51, 52 are structurally separate, and for example, the second carrier element 52 can be encapsulated independently of the first carrier element 51, thereby preventing contamination accordingly.

[0036] If, in an alternative embodiment, the two carrier elements 51 and 52 are understood as the front 51 and back 52 of a single carrier element, then the wire 50 can also be directly formed on the carrier element through the corresponding wire trajectory.

[0037] Furthermore, a sliding contact 30 is provided, movable between the starting point 11 and the ending point 12. In this example, it has two first contacts 31 and two second contacts 32, through which the first contact track 10 and the second contact track 20 are electrically connected. The first contacts 31 independently contact the first contact track 10, and the second contacts 32 independently contact the second contact track 20, wherein the contacts 31 and 32 have parallel, i.e., equally independent sliding paths or define these paths on their respective contact tracks 10 and 20.

[0038] In order for the contacts 31 and 32 to fit elastically onto their respective contact tracks 10 and 20, each contact is equipped with a spring 33 and 34. In this example, the contacts 31 and 32 and their respective springs 33 and 34 are integrally formed as spring arms.

[0039] Since multiple first contacts 31 are pressed against the first contact rail 10 by a spring 33, and multiple second contacts 32 are pressed against the second contact rail 20 by a spring 34, the possibility of all first contacts 31 or all second contacts 32 simultaneously losing electrical contact with their respective contact rails 10 and 20 is very small, thus providing a continuous output signal at the circuit output terminal 53.

[0040] Furthermore, since the second contact 32 does not move directly on the resistor track 40, no mechanical wear occurs on the resistor track, thus significantly improving its lifespan, and allowing the use of inexpensive materials for the resistor track 40.

Claims

1. A control circuit for speed control of an electric handheld tool (1), It has a first contact track (10) that extends continuously from the starting point (11) to the ending point (12) and is connected to the circuit output terminal (53). It has a second contact track (20) that extends parallel to the first contact track (10) and is formed by a plurality of sequentially arranged and mutually insulated contact surfaces (21, 22, 23), with a ground potential (GND) applied at the first contact surface (21) of the arrangement and a power supply voltage (VCC) applied at the last contact surface (23) of the arrangement. It also has a sliding contact (30) movable between the starting point (11) and the ending point (12), the sliding contact having 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), through which the first contact track (10) and the second contact track (20) are electrically connected. It also has a plurality of resistors (41, 42, 43) connected in series, wherein taps (44) are provided at the first resistor (41) and the last resistor (43) in series and between every two resistors (41, 42, 43), and each tap (44) is connected to a contact surface (11, 12, 13) of the second contact rail (20), such that the voltage applied at the circuit output terminal (53) can be graded between the ground potential (GND) and the power supply voltage (VCC) by moving the slider (30), and the slider has no physical contact with the resistors (41, 42, 43).

2. The control circuit according to claim 1, in, The sliding contact (30) has a plurality of first contacts (31) and a plurality of second contacts (32).

3. The control circuit according to claim 2, in, The first contact (31) and the second contact (32) are elastically supported independently of each other, contact their respective contact tracks (10, 20) independently of each other, and have parallel sliding paths on their respective contact tracks (10, 20).

4. The control circuit according to any one of claims 2 or 3, in, The second contact (32) is designed such that at least one second contact (32) remains in contact with at least one of the contact surfaces (21, 22, 23) during the movement of the sliding contact (30) from the starting point (11) to the ending point (12).

5. The control circuit according to any one of claims 2 to 4, in, The second contact (32) is designed such that, during the movement of the sliding contact (30) from the starting point (11) to the ending point (12), all the second contacts (32) always remain in contact with the same contact surface (21, 22, 23) or the same contact surface (21, 22, 23).

6. The control circuit according to any one of claims 2 to 5, in, The first contacts (31) are elastically supported by first springs (33), and the first springs (33) have different resonant frequencies and / or spring constants. And / or wherein the second contact (32) is elastically supported by a second spring (34), and the second springs (34) have different resonant frequencies and / or spring constants relative to each other.

7. The control circuit according to any one of claims 2 to 6, in, The first contacts (31) are staggered from each other in the longitudinal direction of the first contact track (10). And / or wherein the second contact (32) is arranged offset from each other in the longitudinal direction of the second contact track (20).

8. The control circuit according to any one of the preceding claims, in, The contact surfaces (21, 22, 23) are designed as parallelograms or rhombuses.

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

10. The control circuit according to any one of the preceding claims, in, The series-connected resistors (41, 42, 43) form a resistor track (40), and the taps (44) are arranged on the resistor track at regular intervals.

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