EP2484494B1 - Hand tool with a temperature-dependent sensor - Google Patents

Description

The invention relates to a hand machine tool, in particular an electric screwdriver, according to the preamble of claim 1.

Such a hand machine tool is for example in EP 1 780 867 A2 explained.

An electric motor of a hand-held power tool, for example a screwdriver, but also an electric motor of another electrical device, for example a vacuum cleaner, should not overheat during operation so that there is no damage. Temperature-dependent resistors are generally used as sensors to determine the motor temperature. The usual sensors, in particular so-called PTC resistors (PTC), have strongly non-linear temperature-dependent characteristics. When a certain temperature is reached, the resistance value of the PTC thermistor increases extremely, whereupon the control device switches off the electric motor so that it can cool down. As a rule, the hand machine tool cannot be used for a certain time. A typical characteristic of a PTC thermistor is in Figure 2a shown. As a rule, however, exact temperatures cannot be measured with a PTC thermistor. The The temperature cut-off limit is determined empirically based on a few tests.

In the case of a so-called thermistor (NTC), which can also be used as a sensor, the characteristic is not entirely, but essentially linear, which is exemplified in Figure 2b is shown. If the thermistor resistance is installed on the electric motor, for example, the actual temperature values determined by the sensor designed as a thermistor, for example, do not represent the actual, higher temperature of the electric motor, but a lower temperature, so that the control device does not switch off the electric motor in good time and the electric motor overheated. The actual temperature values follow the actual temperature of the electric motor in this example. If, for example, a screwdriver, for example a cordless screwdriver, blocks due to a strong resistance, a large current flows through the electric motor, causing it to heat up quickly in a short time. However, the thermistor cannot detect the high temperature quickly enough due to its "inertia", an unfavorable heat flow to it or the like, so that the control device does not switch off the electric motor. The electric motor can be destroyed.

It is therefore the object of the present invention to provide an improved temperature shutdown of an electric motor.

To achieve the object, a hand machine tool is provided in accordance with the technical teaching of claim 1.

A basic idea of the invention is to dynamically adapt the temperature cut-off limit value so that the respective machine-typical. i.e. e.g. characteristic of the sensor, which is dependent on further parameters, finds its way into the switch-off limit value. This characteristic curve does not only depend on the electrical properties of the sensor, for example the thermistor, but also, for example, on the installation position of the sensor on the electric motor or with respect to the electric motor, its construction and the like. Although the sensor, e.g. the thermistor, has a certain "detection inertia", i.e. A relatively high temperature cut-off limit can be permitted so that the actual temperature values determined by him cannot correspond to the actual temperature of the electric motor, so that the electric motor and thus the hand machine tool can be used up to the respective power limit. The electric motor therefore does not switch off "too early", but can deliver its maximum output, which is particularly advantageous in the case of display devices. Nevertheless, the control device according to the invention switches the electric motor off in good time before it overheats.

According to the invention, it is provided that the control device changes the temperature cut-off limit value depending on an actual gradient representing the respective gradient of a curve of the actual temperature values. Thus, the control device can react to the "dynamics" of the curve. If a relatively small temperature increase (small actual gradient) can be observed, the temperature switch-off limit value can be relatively high. However, if the temperature rises rapidly and steeply, the control device acts, so to speak, and lowers the temperature cut-off limit.

However, a variant of the invention can also provide that the control device compares, for example, the course of the actual temperature values with one or more curves that are stored, for example, in or in the control device or in a memory assigned to it. For example, a temperature switch-off limit value can be assigned to the respective stored curve, so that the control device can independently determine an "ideal" temperature switch-off limit value that "fits" to the current profile of the actual temperature values.

If the control device is designed to correct the temperature cut-off limit value on the basis of gradient monitoring, it is advantageous if it determines the temperature cut-off limit value on the basis of a comparison of the actual gradient value with at least one maximum gradient value, which represents a maximum permissible increase or decrease in the Actual temperature values are represented. If the slope of the actual temperature values increases or decreases, the control device corrects the temperature cut-off limit value.

It is preferably provided that the control device determines the temperature switch-off limit value on the basis of a comparison of the actual gradient value with at least one maximum gradient value, which represents a maximum permissible rise and / or fall of the actual temperature values. This means that, for example, there are two maximum gradient values, one for the permissible rise and another for the permissible drop in the actual temperature values.

As indicated above, it is possible for the control device to use only one or two maximum gradient values for comparison with the actual gradient value. However, it is also possible for the control device to compare the temperature cut-off limit value on the basis of a comparison with a plurality of gradient values, for example with gradient values which are dependent on the actual temperature values. These gradient values can, for example, be contained in a table, determined using a formula or the like. Thus, a constant maximum gradient value is not assumed, but a variable or a number of several gradient values, which serve as a basis for comparison for comparison with the actual gradient value.

The control device can correct the temperature cut-off limit value according to the invention in a variety of ways, for example when the actual gradient value exceeds or falls below the maximum gradient value (s). A correction can, for example, provide that the control device changes the temperature cut-off limit value on the basis of a correction value. The correction value can be a constant correction value, but also a variable correction value. For example, a variable correction value can depend on the actual gradient value, on the actual temperature values or the like. Furthermore, it is possible for the control device to calculate the temperature cut-off limit value using a formula, for example a formula that contains the actual gradient value.

wobei:

• TAneu der neue (zu berechnende) Temperatur-Abschaltgrenzwert,
• TAakt der aktuelle (noch nicht korrigierte) Temperatur-Abschaltgrenzwert,
• GRist der Ist-Gradientenwert und
• Korr ein Korrekturwert sind.

The formula can be, for example: $$\mathrm{TAneu}=\mathrm{TAakt}-\left(\mathrm{Grist}*\mathrm{corr}\right)$$

in which:

• TAnew the new (to be calculated) temperature cut-off limit,
• TAakt the current (not yet corrected) temperature cut-off limit,
• GR is the actual gradient value and
• Corr are a correction value.

The control device can correct the temperature cut-off limit value, for example on the basis of time conditions, on the basis of a control command or the like. For example, the hand machine tool and / or the control device can have a switching input via which the control device can be controlled to correct the temperature cut-off limit value. A learning mode of the control device can be activated, for example, via this switching input, in the course of which the control device corrects the temperature cut-off limit value. For example, the user can activate the control input in the event of a high load on the hand machine tool, so that the control device can adjust to this case, i.e. sets the temperature cut-off limit value so that overheating does not occur at maximum load, but at the same time high performance of the hand machine tool can be called up.

However, temporal conditions for the correction of the temperature cut-off limit value and / or an “automatic correction” are preferred:
The control device can cyclically check the course of the actual temperature values, for example, in order to correct the temperature cut-off limit value. The cycle can be a fixed cycle. For example, it is possible that the Control device after the detection of a certain number of actual temperature values, for example 100 actual temperature values, corrects the temperature cut-off limit value (if necessary). If the actual temperature values are recorded at intervals of, for example, 1 ms, the temperature cut-off limit value is checked every 100 ms and corrected if necessary.

It is also possible for the control device to change a cycle time for the cyclical correction of the temperature cut-off limit value depending on the respective actual gradient value and / or depending on the respective actual temperature value. It is possible, for example, for the control device to check and, if necessary, correct the temperature cut-off limit value more frequently than in the case of smaller actual gradient values in the event of a relatively high increase (or decrease) in the actual temperature values. It is also possible that the temperature cut-off limit value is corrected more frequently at relatively high temperatures than at lower actual temperature values which are less critical for the electric motor.

Furthermore, it is expedient if the control device has a filter for filtering and or smoothing the course of the actual temperature values or the actual gradient value. Thus, for example, "outliers" are eliminated from these values.

The temperature-dependent sensor is expediently an NTC resistor, that is to say a so-called thermistor. In any case, it is advantageous if the sensor is a temperature-dependent resistor. This means that, for example, a so-called PTC resistor could also be used.

Figur 1

eine Seitenansicht einer erfindungsgemäßen Hand-Werkzeugmaschine,

Figur 2a

einen Temperaturverlauf eines bei der Hand-Werkzeugmaschine nicht verwendeten Kaltleiters (PTC-Widerstands),

Figur 2b

einen Temperaturverlauf eines Sensors in Gestalt eines so genannten Heißleiters (NTC-Widerstands) der bei der Hand-Werkzeugmaschine gemäß Figur 1 eingebaut ist,

Figur 3

ein Schaltbild der Hand-Werkzeugmaschine gemäß Figur 1 mit einer erfindungsgemäßen Steuerungseinrichtung,

Figur 4

einen Verlauf eines von der Steuerungseinrichtung gemäß Figur 3 korrigierten Temperatur-Abschaltgrenzwerts, und

Figur 5

ein Ablaufdiagramm, gemäß dem die Steuerungseinrichtung gemäß Figur 3 beispielsweise arbeitet.

An exemplary embodiment of the invention is explained below with reference to the drawing. Show it:

Figure 1

a side view of a hand machine tool according to the invention,

Figure 2a

a temperature profile of a PTC resistor (PTC resistor) not used in the hand machine tool,

Figure 2b

a temperature profile of a sensor in the form of a so-called thermistor (NTC resistor) according to the hand machine tool Figure 1 is installed,

Figure 3

2 shows a circuit diagram of the hand machine tool according to FIG. 1 with a control device according to the invention,

Figure 4

a course of a by the control device Figure 3 corrected temperature cut-off limit, and

Figure 5

a flowchart according to which the control device according to Figure 3 for example works.

A hand-held machine tool 10 is designed as a screwdriver 50, for example as a cordless screwdriver or mains-operated screwdriver. For example, a power plug 11 for connection to a power grid (not shown) and or an electrical energy store 12, for example a battery pack, is present in the hand machine tool 10.

An electric motor 15 can be switched on and off with a switch 14 that can be actuated, for example, by a pushbutton 13. Furthermore, the speed of the electric motor 15 can be set with the switch 14. The electric motor 15 drives, for example, via a gear (not shown) or directly a tool holder 16 into which, for example, a screwdriver bit 67 can be inserted. Of course, other tools can also be introduced on the tool holder 16, for example a drill chuck 17.

The tool holder provided on an output 60 rotates e.g. about an axis of rotation 61.

The pushbutton 13 is located on a handle section 18 of a housing 19 of the hand machine tool 10, which the electric motor 15 in a drive section 20 of the housing 19th

The electric motor 15 has a stator 21 and a rotor 22 which is rotatably mounted on or in the stator 21. An output shaft 23 is motionally coupled to the tool holder 16, for example via a gear.

Exciter windings 24 are provided on the stator 21 and are supplied with electrical current by a current supply device 25 via lines 26. The current supply device 25 is connected via lines 33 to an energy source (for example the power grid) or the energy store 12. The energization device 25 is expediently connected to a rotation angle sensor 27 arranged on the electric motor 15. The energization device 25 has electrical components 28, for example a capacitor, power transistors, logic elements and the like, which are arranged on a circuit board 29.

A control device 30 is provided for controlling the hand machine tool 10, in particular its electric motor 15. The control device 30 is connected to the energization device 25 via lines 31. The control device 30 is arranged together with the switch 14 on a circuit board 32, this being to be understood only as an example, since for example the control device 30 could also form a structural unit with the current supply device 25.

The electric motor 15 is, for example, an electronically commutated electric motor, whereby the principle according to the invention, which will be described later, can of course also be used with other motor types without any problems.

When the electric motor 15 is actuated, the control device 30 also monitors its respective temperature in order to retrieve the highest possible optimal performance of the electric motor 15, so that, for example, screws with high torque can be screwed in, but the electric motor 15 does not overheat.

A temperature-dependent sensor 35 is arranged in the area of the excitation windings 24 in the electric motor 15. The sensor 35 is, for example, a temperature-dependent resistor 55, for example a so-called thermistor, that is to say an NTC resistor, the characteristic curve of which is shown in FIG Figure 2b is indicated. For example, the sensor 35 has a resistance in the range of 1 kilohm at a temperature of -20 ° C. In the range of 0 ° C the resistance is still around 400 ohms and then continues to decrease to around 100 ohms to 40 ° C. This exemplary temperature characteristic curve 36 of the sensor 35 is therefore essentially linear in comparison to, for example, one in Figure 2a shown characteristic curve 34 of a PTC thermistor (PTC resistor), which is low in the range of about - 30 ° C to about 95 ° C and is below a resistance value of about 10 kilo-ohms, but then abruptly to a value of about 80 kilo-ohms increases at about 150 ° C.

The sensor 35 is connected to the control device 30 via a line 37, via which the sensor 35 transmits actual temperature values Tact to the control device 30. The actual temperature values Tist are, for example, resistance values. An exemplary course of the resistance values or the actual temperature values T actual is shown in Figure 2b shown.

Switch-off means 38 of the control device 30 compare a respective actual temperature value T actual with a temperature switch-off limit value TA. When the temperature cut-off limit value TA is reached, the cut-off means 38 switch off the electric motor 15, i.e. the excitation windings 24 are no longer energized. This prevents the electric motor 15 from overheating.

The functional sequence of the control device 30 thus runs, for example, as in FIG Figure 5 shown:
In a step S1, the control device 30 receives a respective actual temperature value Tact and enters it in a step S2, for example in a table 39 which is expediently stored in a memory 40. In a step S3, the control device 30 compares the actual temperature value Tact with a temperature cut-off limit value stored in the memory 40 TA. If the actual temperature value Tist is smaller than the temperature switch-off limit value TA, the control device 30 returns to step S1 and waits for the next actual temperature value Tist, calls it up, or the like.

However, if the actual temperature value Tact is greater than or equal to the temperature switch-off limit value TA, the control device 30 branches to a step S4 and switches off the electric motor 15 for a fixed or expediently adjustable waiting time TW. After the waiting time TW, the electric motor 15 has cooled somewhat, so that the control device 30 can continue with step S5 or S1.

The control device 30 carries out the aforementioned steps regularly, so that the temperature of the electric motor 15 does not rise above an admissible level. However, the sensor 35 is not arranged directly in the inner area or core area of the electric motor 15, but is relatively easy to maintain and / or easy to install, for example in the area of winding heads of the excitation windings 24. This makes it possible for the electric motor 15 to become relatively hot in its core area before this is reflected in higher temperatures in the area of the sensor 35. In particular, rapid temperature increases occur when the electric motor 15 is heavily loaded in a short time. If, for example, the electric motor 15 is initially cold and is then heavily loaded, for example because a screw to be screwed blocks but the expedient torque cutoff does not yet react, this can lead to a very high, rapid temperature rise in the electric motor 15. The invention remedies this as follows:
After each cycle or after a series of cycles in the course of which steps S1 to S3 or S4 are carried out, for example 100-300 cycles which are each run through every millisecond (for example, waiting times can also be provided in steps S3 or S4 or If the respective cycle is only called up every millisecond by a processor 41 of the control device 30), the control device 30 corrects the temperature switch-off limit value TA, if necessary.

The control device 30 increments a cycle counter Z, for example after step S3 or S4 or in a step S5. If the cycle counter Z has a predetermined value Zmax, for example 100 or 300, if 100 or 300 cycles S1 to S3 or S1 to S4 have been completed , after the corresponding test step S6, the control device does not call step S1, but rather the correction routine described below.

In a step S7, the control device 30 determines an actual gradient value GRist, which represents the current gradient of the actual temperature values. For example, the control device 30 determines the actual gradient value GRist using the table 39. For example, it is possible for the control device 30 to determine the actual gradient value GRist using the current actual temperature value and the actual temperature value preceding it. It would then be sufficient to only save the last actual temperature value Tact, i.e. for example, that table 39 would have only one row.

However, it is also possible for the control device 30 to have a plurality of actual temperature values T actual, which are stored in the table 39, in order to form the actual gradient value GR actual uses, for example 2 or more. It is advantageous if the control device 30 carries out, for example, averaging, smoothing or filtering the actual temperature values in order to eliminate "outliers" of the actual temperature values. Then table 39, which contains several actual temperature values, is advantageous.

In a step S8, the control device 30 checks whether the actual gradient value GRist, which was determined in step S7, is greater than a maximum gradient value GRmax, which is stored in the memory 40, for example.

If this is not the case, the control device 30 branches to step S9 and resets the cycle counter Z to zero. From step S9, the control device 30 then returns to step S1.

If, however, the actual gradient value is greater than or equal to the maximum gradient value, the control device 30 branches from step S8 to a step S10, in which it corrects the temperature switch-off limit value TA. For example, the control device 30 uses the formula (1).

For example, if the entry of the actual temperature was particularly large at a time t1, i.e. the actual gradient value dT1 / s is high, the control device 30 corrects the temperature switch-off limit value TA relatively strongly downward, so that it is ensured that the switch-off means 38 switch off the electric motor 15 in good time before a possible overheating.

However, the further temperature rise is somewhat more moderate, so that the control device 30 determines a smaller actual gradient value dT2 / s from a point in time t2, which, however, follows as before is greater than the maximum gradient value. Therefore, the control device 30 lowers the temperature switch-off limit value TA in the respective step S10, but only to a lesser extent (curve 70).

It goes without saying that the control device 30 no longer reduces the temperature switch-off limit value TA when the actual gradient value is no longer greater than the maximum gradient value. Such a profile 71 of the temperature switch-off limit value TA is shown in FIG Figure 4 indicated by dashed lines.

Furthermore, it is also possible for the control device 30 to also raise the temperature switch-off limit value TA again if the actual gradient value is, for example, significantly smaller than the maximum gradient value, in particular for a certain period of time. This period of time can preferably be determined or programmed by parameterization. Thus, for example, a relatively strong correction of the temperature switch-off limit value TA can take place at time t1 in order to provide a certain degree of certainty that the electric motor 15 is switched off in good time before possible overheating. If, however, in the further course or operation of the electric motor 15 it turns out that the actual gradient value GRist remains below the critical threshold, the maximum gradient value GRmax, for a longer time, the control device 30 can accordingly raise the temperature switch-off limit value TA again ( Course 72).

The control device 30 also learns when the electric motor 15 is operating.

From step S10, control device 30 returns to step S1.

Claims (9)

1. Hand-operated power tool, in particular electric screwdriver (50), with a control unit (30) for controlling an electric motor (15) provided with a temperature-dependent sensor (35), in particular a resistor (55), on the basis of temperature actual values (Tist) determined by the temperature-dependent sensor (35), wherein the control unit (30) has switch-off means (38) to switch off the electric motor (15) with the aid of a comparison of the respective temperature actual value (Tist) with a temperature switch-off threshold (TA), characterised in that the control unit (30) is designed for correction of the temperature switch-off threshold (TA) depending on a progression of the temperature actual values (Tist), and that the control unit (30) is designed to vary the temperature switch-off threshold (TA) depending on an actual gradient value (GRist) representing the respective gradients of a progression curve of the temperature actual values (Tist).
2. Hand-operated power tool according to claim 1, characterised in that the control unit (30) determines the temperature switch-off threshold (TA) with the aid of a comparison of the actual gradient value (GRist) with at least one maximum gradient value (GRmax) which represents a maximum permissible rise and/or fall of the temperature actual values (Tist).
3. Hand-operated power tool according to claim 1 or 2, characterised in that the control unit (30) determines the temperature switch-off threshold (TA) with the aid of a comparison of the actual gradient value (GRist) with gradient values dependent on the temperature actual values (Tist).
4. Hand-operated power tool according to any of the preceding claims, characterised in that the control unit (30) changes the temperature switch-off threshold (TA), in particular if the maximum gradient value or values (GRmax) is or are exceeded by the actual gradient value (GRist), by a correction value containing the gradient value, and/or calculates it with the aid of a formula containing the actual gradient value (GRist).
5. Hand-operated power tool according to any of the preceding claims, characterised in that the control unit (30) makes cyclical checks of the progression of the temperature actual values (Tist) for correction of the temperature switch-off threshold (TA).
6. Hand-operated power tool according to claim 5, characterised in that the control unit (30) varies a cycle time for cyclical correction of the temperature switch-off threshold (TA), depending on a or the particular actual gradient value (GRist) and/or depending on the respective temperature actual value (Tist).
7. Hand-operated power tool according to any of the preceding claims, characterised in that the control unit (30) has a filter for filtering and/or smoothing the progression of the temperature actual values (Tist) and/or the actual gradient value (GRist).
8. Hand-operated power tool according to any of the preceding claims, characterised in that the temperature-dependent sensor (35) forms or includes a resistor (55), in particular an NTC resistor (55).
9. Control unit (30) for a hand-operated power tool (10) or a suction unit for controlling an electric motor (15) provided with a temperature-dependent sensor (35), in particular a resistor (55), on the basis of temperature actual values (Tist) determined by the temperature-dependent sensor (35), wherein the control unit (30) has switch-off means (38) to switch off the electric motor (15) with the aid of a comparison of the respective temperature actual value (Tist) with a temperature switch-off threshold (TA), characterised in that the control unit (30) is designed for correction of the temperature switch-off threshold (TA) depending on a progression of the temperature actual values (Tist), and that the control unit (30) is designed to vary the temperature switch-off threshold (TA) depending on an actual gradient value (GRist) representing the respective gradients of a progression curve of the temperature actual values (Tist).

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