EP2213420B1 - Control method and power tool - Google Patents

Abstract

The method involves longitudinally detecting an acceleration of a stroke axis of a hand tool machine i.e. electro pneumatic chipping hammer. A drive power is reduced when the detected acceleration is greater than a threshold value, which is selected greater than maximum acceleration value. A percussive operation of the machine is performed on a workpiece. A speed of a drive shaft is adjusted for adjusting the drive power. A time period of the machine is selected depending upon the speed of the drive shaft. An independent claim is also included for a hand tool machine comprising a drive shaft.

Description

FIELD OF THE INVENTION

The present invention relates to a method for controlling a pneumatic, in particular electro-pneumatic, striking hand tool according to the preamble of claim 1 and an electropneumatically striking hand tool according to the preamble of claim 12. In particular, the method is a control method for reducing idle strokes of a power tool.

DESCRIPTION OF THE PRIOR ART

From the EP 0 303 651 B1 is a method for interrupting a drive operation for an electro-pneumatic chisel hammer and hammer drill known. This method is used in case of blocking to interrupt the drive train to protect a user. A blockage of a chisel hammer is detected by a position of a tool or an impactor in a striking mechanism. Blocking a rotational movement is detected by exceeding acceleration values.

The Indian EP 0 303 651 B1 quoted electro-pneumatic chisel hammer from the DE 28 20 128 switches off due to construction, if a user raises the chisel hammer. A tool falls into a strike axis mounted stop. A flying mass can now fly forward to the extent that the flying mass does not further close a ventilation opening in the guide tube between the flying mass and an exciter piston. The excitation piston can no longer suck in the flying mass because a pressure equalization takes place via the ventilation opening. The impact mechanism is thus deactivated in a passive manner. As soon as the user touches the chisel hammer, the flying piston is pushed over the ventilation opening by the tool. The exciter piston can suck in the flying piston again and the hammer mechanism is active.

EP 1 170 095 A2 describes a striking electric hand tool according to the preamble of claim 12 and a method according to the preamble of claim 1, with a motor-driven pneumatic percussion. A control unit monitors a position of one of the beating elements, eg tool, striker, flying piston. If the beating element shifts in a position that is prominent for a blank, a speed of the driving motor is lowered to 10% to 50% of a working speed.

DISCLOSURE OF THE INVENTION

The present invention provides a method according to claim 1, which reduces a power consumption of an electropneumatically striking hand tool when lifting from a workpiece, i. if no counterforce acts on an electropneumatic impact mechanism.

The inventive method according to claim 1 for controlling an electropneumatically striking hand tool machine performs the following steps. An acceleration is detected, which acts along a direction of impact of the power tool. A drive power is reduced when the detected acceleration is greater than a threshold value, wherein the threshold value is selected to be greater than accelerations that occur during a striking operation of the power tool on a workpiece.

A flying piston periodically strikes a tool, possibly via an intermediate striker, when the tool is in contact with a workpiece, i. in the intended application mode. The impulse and the kinetic energy of the flying piston are transmitted to the tool and the workpiece. The occurring acceleration values of the coupled system of flying piston and tool are due to their common mass low. In addition, the flying piston or the anvil is typically stopped by the tool before they reach a corresponding catching device in the direction of impact. The acceleration values transferred to the hand tool machine during hitting are low in the intended application mode.

When blanking, i. the tool has no contact with a workpiece, the momentum and the total kinetic energy of the flying piston are transmitted to the catching device of the power tool. There are comparatively large acceleration values compared to the intended application mode.

The occurring accelerations, e.g. The corresponding peak values, both in the intended operation and when emptying are given for by the structure and performance of a power tool, possibly even by the tool. The acceleration values can be measured for a type of hand tool. The threshold value can be selected taking into account the measured values.

One aspect of the invention relates to a portable power tool according to claim 12 having a drive shaft, a pneumatic impact mechanism, an acceleration sensor and an evaluation device for carrying out the above-mentioned control method.

According to the invention, detection of a look-up is carried out by checking at least one of the following criteria. First criterion: the acceleration occurs in the direction of impact and exceeds the threshold value; Second criterion: the acceleration exceeds in terms of magnitude the threshold twice in the interval of a first period of time and third criterion: the acceleration exceeds in terms of amount the threshold twice within a second period of time. The drive power is reduced when a lookup is detected.

In the subclaims embodiments of the inventive control method are described.

In a hard placing the power tool on a workpiece, a high acceleration may occur, which exceeds the threshold amount. In this case, however, the performance should not be reduced because a user now wants to remove material from the workpiece. Blanking can be distinguished from hard placement based on the direction of acceleration. In a hard touch the forces from the tool in the direction of the power tool act. When blanking occur both forces in as well as against the direction of impact. Therefore, it may prove advantageous to determine a blanking on the basis of the forces occurring in the direction of impact and / or based on a double crossing of the negative and the positive peak values of the acceleration. It can also be used that a blanking occurs with a predetermined period.

An embodiment provides that, for the third criterion, either the acceleration in each case once in the direction of impact and against the direction of impact exceeds the threshold value in absolute terms, or the acceleration between the two times exceeding the threshold value goes back to zero. The second period of time may be selected to be shorter than a period between two strokes of a beating operation on a workpiece.

Blanking occurs periodically, with the period dictated by the drive. An embodiment provides that the first period is selected depending on a current speed of a drive shaft. The first time span may be the inverse of the current speed.

A further embodiment provides that after detection of a lookup, the drive power is lowered from a high drive power to an average drive power. A single exceeding of the threshold value can be done by an unforeseen event. As soon as a subsequent exceeding, which is to be expected when looking up, does not occur, the drive power can be quickly increased again. Otherwise, the drive power is already reduced and decreasing to a low drive power sleep mode can be as fast.

A development provides that the drive power is lowered to a low drive power, if after the detection of a lookup within a third period another lookup is detected.

If, after detecting a lookup within a fourth time period, no further lookup is detected, the drive power is increased to the high drive power. The control method provides the full power of the drive and starts again from the beginning when no more lookup is detected. For example, the lookup is triggered when the user places the hand tool on a workpiece or when a flying piston of a percussion mechanism comes to rest.

The third and / or fourth time period can be selected as a function of a current rotational speed of a drive shaft. A lookup takes place in a rhythm which is predetermined by the drive shaft. Therefore, based on the rotational speed, it can be determined at which time interval after a first look-up a second look-up would have to take place.

In a further development, a speed of a drive shaft is adjusted for adjusting the drive power. A low speed for the low drive power can be selected with less than 35% of a high speed for the high drive power. An average speed for the average drive power can be selected between 75% and 85% of a high speed for the high drive power. A resonant speed resonantly excites a pneumatic hammer mechanism of the hand tool machine and a high speed, which deviates by less than 10% from the resonant speed, can be selected for the high drive power. The resonant excitation is characterized by the fact that the excitation power is transmitted to the striking mechanism with the highest efficiency.

An embodiment provides that the acceleration sensor and the evaluation device are integrated in an electronic module.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

einen elektropneumatischen Meisselhammer;

Fig. 2

ein Schlagwerk eines elektropneumatischen Meisselhammers;

Fig. 3

schematisierte Beschleunigungswerte beim Betrieb eines Meisselhammers und

Fig. 4

ein Flussdiagramm eines Steuerungsverfahrens.

The following description explains the invention with reference to exemplary embodiments and figures. In the figures show:

Fig. 1

an electro-pneumatic chisel hammer;

Fig. 2

a striking mechanism of an electro-pneumatic chisel hammer;

Fig. 3

schematized acceleration values in the operation of a chisel hammer and

Fig. 4

a flowchart of a control method.

Identical or functionally identical elements are indicated by the same reference numerals in the figures, unless stated otherwise.

EMBODIMENTS OF THE INVENTION

Fig. 1 shows schematically as an example of a striking hand tool an electro-pneumatic chisel hammer 1, other examples not shown are, inter alia, rotary hammers, combi hammers.

In a machine housing 2, a drive train with a primary drive 3, a drive shaft 4 and a striking mechanism 5 is arranged. Between the primary drive 3 and the drive shaft 4, a transmission 7 may be connected. The primary drive 3 is preferably an electric motor, for example a universal motor or a brushless motor. The drive shaft 4 is rotated at speeds in the range between 1 Hz and 100 Hz, for example at 10 Hz to 60 Hz by the primary drive 3. The rotational movement of the drive shaft 4 is transmitted by the striking mechanism 5 in a periodic impact movement along a striking axis 8. A tool held in a tool holder 9 is driven out of the chipping hammer 1 by the periodic impacts along the striking axis 8 in the direction of impact 100. A return of the tool in the chisel hammer 1 against the direction of impact 100 is effected by pressing the chisel hammer 1 to a workpiece.

Fig. 2 shows an exemplary impact mechanism. 5

A guide tube 10 carries an excitation piston 12 and a flying piston 13 along the striking axis 8. The excitation piston 12 and the flying piston 13 are formed in a form-fitting manner to an inner wall 11 of the guide tube 10. An airtight seal can be achieved by sealing rings 15, 16. A first ventilation opening 17 connects an interior of the guide tube 10 with an outer space of the guide tube 10 in the region of the excitation piston 12. A second ventilation opening in the area of the flying piston 13 connects an interior of the guide tube 10 to an outer space of the guide tube 10.

At a tool-side end of the guide tube 10, a striker 20 is mounted in an anvil guide 21. The anvil guide 21 limits movement of the striker 20 in the direction of impact 100 and against the direction of impact 100. A tool-facing end 22 is in contact with a tool which is held in the tool holder 9. A tool-facing end 23 of the striker 20 protrudes from the striker guide 21 in the interior of the guide tube 10th

The exciter piston 12 is forced by the drive shaft 4 to a periodic movement along the striking axis 14. The drive shaft 4 is rotated about its axis of rotation 30 and thereby moves an eccentric to the axis of rotation 30 arranged eccentric pin 31. The eccentric pin 31 is connected to a rod 32 with the excitation piston 12. The half stroke of the exciter piston 12 corresponds approximately to the distance 33 of the eccentric pin 31 from the axis of rotation 30.

Due to a closed by the excitation piston 12 and the air piston 13 in the guide tube 10 air volume of the flying piston 13 follows the forced movement of the excitation piston 12. When the excitation piston 12 is moved in the direction of impact 100, the flying mass 13 is accelerated in the direction of impact 100. The flying piston 13 strikes the tool-facing end 23 of the striker 20. The pulse of the flying piston 13 is thereby transmitted in a quasi-elastic shock on the striker 20 and the tool. The flying mass 13 is accelerated counter to the impact direction 100 by the excitation piston 12 after the impact, when the excitation piston 12 moves counter to the direction of impact 100. The sequence of movements is repeated periodically with a frequency corresponding to the rotational speed of the drive shaft 4.

Fig. 3 schematically shows the occurring acceleration values a in the machine housing 2, plotted over the time t, wherein a positive acceleration value a indicates an acceleration in the direction of impact 100. First, a user sets the Hand tool 1 on the tool (82). Then comes the intended application operation 83, in which the workpiece is processed by the blows of the chisel hammer 1. Subsequently, a whitening occurs 84, because the user lifts the chisel hammer 1, for example, to position it at a different location on the workpiece.

In the intended application mode 83, the impacts of the flying piston 13 on the striker 20 occur periodically at intervals T, which are predetermined by the rotational speed of the drive shaft. The pattern of the acceleration a in one of the beats can be divided into two phases 80, 81. In a first phase 80, a positive acceleration value a1 is detected, that is, an acceleration in the direction of impact 100. This is attributable to the event when the striker 20 and the tool are accelerated out of the machine tool 1. Their acceleration a is presumably partly transmitted to the machine housing 2 due to friction in the striker guide 21 and in the tool receptacle 9 and when the plunger 20 is stopped at the tool-facing end 24 of the striker guide 21. In the second phase 81, a negative acceleration value a2 is detected, to which presumably a relaxation in the impact of elastically deformed components and / or a return of the striker 20 at the end 25 of the striker guide 21 contribute. The peak values and the time integrals of the positive acceleration value a1 and the negative acceleration value a2 may differ, but are typically not different by more than a factor of two.

If a user lifts the chisel hammer 1 from the workpiece, the striker 20 and the tool can not deliver the impulse transmitted by the missile 13 to a workpiece, but strike the respective ends 24 of their guides 21 unrestrained. This is referred to as a blank. This results in high acceleration values a3, a4 in the engine housing 2 during idling 84. The amplitude of the acceleration values a3, a4 is at least a factor of two greater than the acceleration values a1, a2 during the intended time, depending on the design of the chisel hammer 1 and the mass of the tool Application mode 83, ie when hitting a workpiece.

There are known passive solutions that prevent a periodic occurrence of blank spaces. When there is no space, the flying mass 13 has to travel a greater distance, since the beatpiece 20 is displaced in the direction of impact 100. The distances are dimensioned such that the idling a movement of the flying piston 13 from resonance to the excitation by the excitation piston 12 device. In addition, the vent opening 18 can be arranged so that the vent opening 18 at a Leerschlag the interior of the guide tube 10 between the air piston 13 and the excitation piston 12 ventilated. The movement of the flying piston 13 to the excitation piston 12 is decoupled so far that the flying piston 13 between the striker 20 and the vent opening 18 stops. The design freedom, in particular the length of a percussion mechanism 5 is thus limited by the desired shutdown when idling.

A blank 84 may also be divided into two phases 85, 86. In the first phase 85, a positive acceleration value a3, i. an acceleration a in the direction of impact 100. The positive acceleration value a3 correlates among other things with the striking of the missile 13 and / or the striker 20 in tool-facing ends 24 of their guides 10, 21. In the second phase 86 results in a negative acceleration value a4, presumably a relaxation of components elastically deformed during the first phase 85 and / or a rebound of the striker 20 at the end 25 of the striker guide 21. The time interval between two empty beats corresponds to the period T or the specification by the current rotational speed of the drive shaft 4.

The placement 82 of the chisel hammer 1 on a workpiece has a different signature with respect to the occurring acceleration a5. The acceleration value a5 may be approximately equal to the absolute acceleration values a3, a4. The amplitude and time integral of the acceleration values at touch-up are greatly affected by a user, a workpiece, and a situation, such as a posture. in a breakthrough, depending. However, the impact typically exhibits only a single phase with negative acceleration values, that is to say an acceleration a opposite to the direction of impact 100, during placement. In addition, the chisel hammer is usually reset a few seconds apart, so that within a period T a corresponding acceleration a5 occurs only once.

When placing the chisel hammer 1, a user typically wants the maximum impact power available. When picking up the chisel hammer 1, whitening should be suppressed as much as possible in order to reduce the load on the chisel hammer 1 and the user.

In connection with the flowchart of Fig. 4 an exemplary control method for the chisel hammer 1 is described.

In response to actuation of a system switch 40, a system controller 41 is activated or triggered. The system controller 41 instructs a motor controller 42 to accelerate the primary drive 3 (S1). The speed N of the drive shaft 4 reaches a high speed N1. The high speed N1 can be in the range of 80% to 100% of the nominal maximum speed. The high speed N1 is preferably matched to the impact mechanism 5, that the excitation piston 12, the movement of the flying piston 13 resonantly excites. When the high speed N1 is reached, the impact mechanism 5 strikes at a distance of the period T (S2). The period T between two strokes corresponds to the inverse of the high speed N1 or an integral multiple of the inverse of the high speed N 1.

An acceleration sensor 43 detects the occurring acceleration a. The acceleration sensor 43 may be located in the percussion mechanism 5, on the guide tube 10 impact mechanism 5, in an electronic group for controlling the primary drive 4 away from the percussion mechanism 5, e.g. the system controller 41, or be arranged at other locations within the machine housing 2. The signals of the acceleration sensor 43 are forwarded to an evaluation device 44.

The evaluation device 44 compares the occurring acceleration values a with a threshold value A (S3). The magnitude of the threshold A is greater than the acceleration values a1 that typically occur in the intended application mode 83, and less than the typical acceleration values a5 selected during a blank bump 84. The threshold A is to be adapted to the respective chisel hammer 1 and possibly also to a tool used. In the illustrated embodiment, the evaluation device 44 only responds to positive acceleration values a, i. to an acceleration in the direction of the striking axis 100.

A branch S4 of the control method takes place with the event when the threshold value A is exceeded by a positive acceleration value a (left branch of the flowchart). Otherwise, the evaluation device 44 continues to monitor the occurring acceleration values a (right branch of the flowchart).

In response to an exceeding of the threshold value A, a time t1 of the exceeding can be detected. The evaluation device 44 can, for example, start or reset a timer 45.

The evaluation device 44 instructs the system controller 41 to lower the rotational speed of the drive shaft 4 to an average rotational speed N2 (S5). The average speed N2 may be 15% to 30% lower than the previously set high speed N1.

The evaluation device 44 checks whether within a time period T1 the threshold value A is exceeded once more (S6). The evaluation device 44 can be triggered, for example, by the timer 45, which was previously started or reset by the evaluation device 44. The time period T1 is longer than the period T, for example, up to 50% greater. The time period T1 can be determined as a function of the current average speed N2. When idling 84, a further empty space and corresponding acceleration values a4, a5 are expected within the time period T1 since the last empty space.

A branch S7 of the control method takes place when either the time period T1 is exceeded or the threshold value A is exceeded once more. If, on the one hand, the threshold value A is not exceeded within the time period T1, the speed N of the drive shaft is raised to the high speed N1 (S8). The chisel hammer 1 works again with full power. The control process returns to step S3.

On the other hand, if within the period T1, the threshold value A is exceeded once more, the rotational speed N of the drive shaft 4 is lowered to a low rotational speed N3 (S9). The low speed N3 may be, for example, 10% to 30% of the nominal maximum speed. The low speed N3 is preferably selected so that the excitation of its movement through the excitation piston 12 is out of resonance. The coupling of the movement of the excitation piston 12 to the flying mass 13 is reduced and it can be transmitted less energy. In another embodiment, it is provided to completely switch off the primary drive 3.

In addition, a ventilation opening 18 may be provided, which is at least temporarily opened during idle. The vent opening 18 may be arranged as in the above-described passive Leerschlagdämpfung. The missile 13 closes the ventilation opening 18 when the missile 13 rests against the striker 20 which is fully engaged in the guide tube 10. The vent opening 18 is exposed when the missile 13 may abut a tool-side stop, because the striker 20 is disengaged from the guide tube 10 to a tool-side stop 24. Due to the ventilation opening 18, the coupling of the flying piston 13 is additional weakened and the movement of the flying piston 13 may inter alia come to a standstill due to friction losses.

The evaluation device 44 continuously checks whether further blank beats occur (S10). The timer 45 is reset, for example, each time by the evaluation device 44 when the threshold A is exceeded. If no further exceeding is detected within a second time period T2, the control method branches (S11). The rotational speed N of the drive shaft 4 is increased to the high rotational speed N1 (S12). The control process returns to step S3.

The time period T2 can be selected equal to the time period T1. Alternatively, the time T2 may be up to five times, e.g. the triple, the period T be selected. The time period T2 can be determined as a function of the current low rotational speed N2. If percussion 5 still looks up, time T2 should be chosen so that another beat is expected within T2.

The impact mechanism 5 can transmit less energy to the missile 13 and thus to the striker 20 at the changed low speed N3. The empty space becomes weaker and the acceleration values a4, a5 of the empty space decrease. However, with an increase in the speed of the drive shaft 4 to the high speed N1, the striking mechanism 5 could possibly be excited again. In a further development, therefore, the threshold A is reduced when a first number of idle beats, i. Exceeding the threshold value A, were detected. The first number can be between three and ten. The threshold value A can also be lowered continuously to a lower threshold A2 with each detected blank. The lower threshold value A2 can be, for example, half of the threshold value A, but is greater than the acceleration values a1, a2 in the intended application mode.

After a certain number of clearances, the missile 13 can come to a complete halt. It turns out that the missile 13 comes to a stop between the ventilation opening 18 and the striker 20. Even if now the speed of the drive shaft 4 is increased to the high speed N1, the missile 13 stops. It now requires a placement of the chisel hammer 1 on a workpiece, so that the tool pushes the missile 13 via the vent opening 18 to couple the missile 13 back to the exciter piston 12.

The above-described embodiment distinguishes setting of blanking by two criteria. First, only acceleration values a in the direction of impact 100 are taken into account, and secondly, it is checked whether a second beat (S6) occurs after a first beat (S3). The control procedure can simply apply one of the two criteria.

Another embodiment makes use of the fact that, when placed, the acceleration a has only one phase and, when emptying, two phases. In step S3, after exceeding the threshold value A, it is checked whether the threshold value A is exceeded again within a time period T3. The period of time T3 within which the second phase takes place when looking up is characteristic of a chisel hammer 1. The period of time T3 can thus be measured and stored in the evaluation device 44 stored. A refinement provides that it is checked that the acceleration values in the first and second phases have different signs. Alternatively, it can be checked whether a zero crossing of the acceleration occurs between the two phases. The acceleration a can then be determined without sign. The steps S6 and S10 can be adapted analogously.

In one embodiment, the speed of the drive shaft 4 is lowered directly from the high speed N1 to the low speed N3, when an acceleration a is detected for the first time, which is assigned to a lookup. The steps S5, S6, S7 and S8 can be omitted.

In a further embodiment, the acceleration values are detected by stretch strips. The stretch marks are preferably arranged on the machine housing 2. The occurring accelerations lead to a corresponding compression and expansion of the machine housing 2 or arranged in the machine housing 2 elements. The acceleration is typically detected by the stretch marks as a change in resistance or capacitance.

Claims (13)

1. A method of controlling a pneumatically percussive hand-held power tool characterized by the following steps:

   detecting an acceleration (a) along a percussion axis (8) of the hand-held power tool (1),

   detecting the occurrence of a residual strike by checking at least one of the following criteria,

   first criterion: the acceleration (a) occurs in direction of percussion (100) and its magnitude exceeds a threshold value (A), the threshold value (A) being set greater than maximum acceleration values (a1, a2) occurring during percussive operation of the hand-held power tool (1) on a workpiece;

   second criterion: the magnitude of the acceleration (a) exceeds the threshold value (A) twice in the space of a first time interval (T), which is set as a function of an actual rotational speed (N) of a drive shaft (4), and

   third criterion: the magnitude of the acceleration (a) exceeds the threshold value (A) twice within a second time interval (T3), which is set shorter than a time interval between two impacts during percussive operation; and

   reducing the driving power if a residual strike is detected.
2. A method according to Claim 1, characterized in that, for the third criterion, either the magnitude of the acceleration exceeds the threshold value (A) once in direction of percussion (100) and once counter to the direction of percussion (100), or else the magnitude of the acceleration falls back to zero between the two occasions when it exceeds the threshold value (A).
3. A method according to one of Claims 1 or 2, characterized in that the second time interval (T3) is set shorter than a time interval (T) between two impacts on a workpiece during percussive operation.
4. A method according to one of Claims 1 to 3, characterized in that on detection of a residual strike the driving power is reduced from a high driving power to a medium driving power.
5. A method according to Claim 4, characterized in that if, following detection of a residual strike, a residual strike is once again detected within a third time interval (T2), then the driving power is reduced to a low driving power.
6. A method according to Claim 4 or 5, characterized in that if, following detection of a residual strike, no further residual strike is detected within a fourth time interval (T3), then the driving power is increased to the high driving power.
7. A method according to Claim 5 or 6, characterized in that the third and/or fourth time intervals are set as a function of an actual rotational speed of a drive shaft (4).
8. A method according to one of the preceding claims, characterized in that a rotational speed (N) of a drive shaft (4) is set for adjusting the driving power.
9. A method according to Claim 8, characterized in that a low rotational speed (N3) for the low driving power is set at less than 35% of a high rotational speed (N1) for the high driving power.
10. A method according to Claim 8 or 9, characterized in that a medium rotational speed (N2) for the medium driving power is set at between 75% and 85% of a high rotational speed (N1) for the high driving power.
11. A method according to one of Claims 8 to 10, characterized in that a resonant rotational speed resonantly excites a pneumatic percussion mechanism of the hand-held power tool (1) and a high rotational speed (N) which deviates by less than 10% from the resonant rotational speed is set for the high driving power.
12. A hand-held power tool comprising:

    a drive shaft (4),

    a pneumatic percussion mechanism (5), and

    an acceleration sensor,

    characterized by

    evaluating means for implementing one of the methods according to Claims 1 to 11.
13. A hand-held power tool according to Claim 12, characterized in that the acceleration sensor and the evaluating means are incorporated into one electronic module.

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