Abstract
Percussion unit, especially for a rotary hammer and/or percussion hammer, comprising a control unit which is designed for controlling a pneumatic percussion mechanism. According to the disclosure, the control unit comprises at least one load estimation device.
Claims
1. A percussion mechanism unit for at least one of a rotary hammer and a percussion hammer comprising: a pneumatic percussion mechanism; a motor configured to drive the pneumatic percussion mechanism; and a control unit configured to control the pneumatic percussion mechanism by at least one of open-loop control and closed-loop control, the control unit being further configured to: receive a measured rotational speed of the motor; and estimate an unknown load on the motor caused by a percussion operating mode of the pneumatic percussion mechanism, the unknown load being estimated by subtracting rotational speed fluctuations corresponding to at least one known load from the measured rotational speed; and detect that the pneumatic percussion mechanism is operating in the percussion operating mode in response to the estimated unknown load exceeding a limit value.
2. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to: estimate the unknown load further based on a system model.
3. The percussion mechanism unit as claimed in claim 1, wherein one of the at least one known load is periodic with respect to one of (i) time and (ii) a rotational angle of the motor.
4. The percussion mechanism unit as claimed in claim 1, wherein the unknown load corresponds to a rotational speed fluctuation in the motor caused by the percussion operating mode of the pneumatic percussion mechanism.
5. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to: estimate the unknown load based on the measured rotational speed by filtering the measured rotational speed with a known frequency band of the unknown load.
6. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to: determine the at least one known load in a learning mode.
7. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to estimate a driving torque of a drive unit using a dynamic model.
8. The percussion mechanism unit as claimed in claim 7, wherein the control unit is configured to determine model parameters of the dynamic model from a comparison of measured and estimated parameters.
9. The percussion mechanism unit as claimed in claim 7, wherein the control unit is configured to determine an operating state by comparing at least one parameter with at least one limit value.
10. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured, in at least one operating state, to set at least one operating parameter temporarily to a start value to change from an idling operating mode to a percussion operating mode.
11. The percussion mechanism unit as claimed in claim 10, wherein one of the at least one operating parameter is a throttle characteristic quantity of a venting unit.
12. The percussion mechanism unit as claimed in claim 10, wherein one of the at least one operating parameter is a percussion frequency.
13. The percussion mechanism unit as claimed in claim 1, further comprising: a mode change sensor configured to signal a change of an operating mode.
14. A hand power tool, comprising: a percussion mechanism unit, the percussion mechanism unit comprising: a pneumatic percussion mechanism; a motor configured to drive the pneumatic percussion mechanism; and a control unit configured to control the pneumatic percussion mechanism by at least one of open-loop control and closed-loop control, the control unit being further configured to: receive a measured rotational speed of the motor; and estimate an unknown load on the motor caused by a percussion operating mode of the pneumatic percussion mechanism, the unknown load being estimated by subtracting rotational speed fluctuations corresponding to at least one known load from the measured rotational speed; and detect that the pneumatic percussion mechanism is operating in the percussion operating mode in response to the estimated unknown load exceeding a limit value.
15. A method for estimating a load for a percussion mechanism unit having a pneumatic percussion mechanism, a motor configured to drive the pneumatic percussion mechanism, and a control unit configured to control the pneumatic percussion mechanism by at least one of open-loop control and closed-loop control, the method comprising: receiving a measured rotational speed of the motor; estimating an unknown load on the motor by bandpass filtering the measured rotational speed with a frequency band corresponding to a known percussion frequency of a percussion operating mode of the pneumatic percussion mechanism; identifying whether the pneumatic percussion mechanism is operating in the percussion operating mode based on the estimated unknown load; identifying whether the pneumatic percussion mechanism is operating in an idling operating mode based on the estimated unknown load; and estimating a driving torque of a drive unit using a dynamic model.
16. The percussion mechanism unit as claimed in claim 3, wherein a setpoint value for a rotational speed of the pneumatic percussion mechanism is raised to a speed corresponding to a working frequency in response to the percussion operative mode being identified.
17. The percussion mechanism unit as claimed in claim 1, wherein the rotational speed fluctuations corresponds to at least one of (i) a known variable transmission ratio of the at least one of the rotary hammer and the percussion hammer, (ii) a known motor cyclic irregularity of the at least one of the rotary hammer and the percussion hammer, and (iii) an known irregular voltage supply of the at least one of the rotary hammer and the percussion hammer.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Further advantages are given by the following description of the drawing. The drawing shows four exemplary embodiments of the disclosure. The drawing, the description and the claims contain numerous features in combination. Persons skilled in the art will also expediently consider the features individually and combine them to create appropriate further combinations.
(2) In the drawings:
(3) FIG. 1 shows a schematic representation of a rotary and percussion hammer having a control unit according to the disclosure, in a first exemplary embodiment, in an idling mode,
(4) FIG. 2 shows a schematic representation of the rotary and percussion hammer in a percussion mode,
(5) FIG. 3 shows a representation of a sequence diagram of the control unit during operation of the percussion mechanism,
(6) FIG. 4 shows a representation of a sequence diagram of the control unit in a learning mode,
(7) FIG. 5 shows a representation of parameters that influence a rotational speed signal,
(8) FIG. 6 shows a representation of parameters learned in the learning mode,
(9) FIG. 7 shows a schematic representation of a possible definition of a start value, a limit value, a working value and a maximum value,
(10) FIG. 8 shows a representation of a sequence diagram of the control unit of the percussion mechanism unit in the case of a change between an idling mode and a percussion mode,
(11) FIG. 9 shows a representation of signal spectra of a rotary and percussion hammer in a second exemplary embodiment, in various operating states,
(12) FIG. 10 shows a schematic representation of a rotary and percussion hammer in a third exemplary embodiment, in an idling mode,
(13) FIG. 11 shows a representation of a block diagram of a load observer,
(14) FIG. 12 shows a representation of a system comprising the load observer and a drive unit,
(15) FIG. 13 shows a representation of a motor characteristic curve,
(16) FIG. 14 shows an exemplary representation of an estimated and a measured load moment,
(17) FIG. 15 shows an exemplary representation of the characteristic of the measured and the estimated load moment, and of an operating state of a percussion mechanism,
(18) FIG. 16 shows a schematic representation of a venting unit of a percussion mechanism of a rotary and percussion hammer comprising a percussion mechanism unit, in a fourth exemplary embodiment, and
(19) FIG. 17 shows a further schematic representation of the venting unit.
DETAILED DESCRIPTION
(20) FIG. 1 and FIG. 2 show a rotary and percussion hammer 12a, having a percussion mechanism unit 10a, and having a control unit 14a, which is provided to control a pneumatic percussion mechanism 16a by open-loop and closed-loop control. The percussion mechanism unit 10a comprises a motor 36a, having a transmission unit 38a that drives a hammer tube 42a in rotation via a first gear wheel 40a and drives an eccentric gear mechanism 46a via a second gear wheel 44a. The hammer tube 42a is connected in a rotationally fixed manner to a tool holder 48a, in which a tool 50a can be clamped. For a drilling operating mode, the tool holder 48a and the tool 50a can be driven with a rotary working motion 52a, via the hammer tube 42a. If, in a percussion operating mode, a striker 54a is accelerated in a percussion direction 56a, in the direction of the tool holder 48a, upon impacting upon a striking pin 58a that is disposed between the striker 54a and the tool 50a it exerts a percussive impulse that is transmitted from the striking pin 58a to the tool 50a. As a result of the percussive impulse, the tool 50a exerts a percussive working motion 60a. A piston 62a is likewise movably mounted in the hammer tube 42a, on the side of the striker 54a that faces away from the percussion direction 56a. Via a connecting rod 64a, the piston 62a is moved periodically in the percussion direction 56a and back again in the hammer tube 42a, by the eccentric gear mechanism 46a driven with a percussion-mechanism rotational speed 124a (FIG. 8). The piston 62a compresses an air cushion 66a enclosed, between the piston 62a and the striker 54a, in the hammer tube 42a. Upon a movement of the piston 62a in the percussion direction 56a, the striker 54a is accelerated in the percussion direction 56a. The percussion operating mode can commence. The striker 54a can be moved back, contrary to the percussion direction 56a, by a rebound on the striking pin 58a and/or by a negative pressure that is produced between the piston 62a and the striker 54a as a result of the backward movement of the piston 62a, contrary to the percussion direction 56a, and/or by a counter-pressure in a percussion space 134a between the striker 54a and the striking pin 58a, and can then be accelerated for a subsequent percussion impulse back in the percussion direction 56a. Venting openings 68a are disposed in the hammer tube 42a, in a region between the striker 54a and the striking pin 58a, such that the air enclosed between the striker 54a and the striking pin 58a in the striking space 134a can escape. Idling openings 70a are disposed in the hammer tube 42a, in a region between the striker 54a and the piston 62a. The tool holder 48a is mounted so as to be displaceable in the percussion direction 56a, and is supported on a control sleeve 72a. A spring element 74a exerts a force upon the control sleeve 72a, in the percussion direction 56a. In a percussion mode (FIG. 2), in which the tool 50a is pressed against a workpiece by a user, the tool holder 48a displaces the control sleeve 72a against the force of the spring element 74a such that it covers the idling openings 70a. If the tool 50a is taken off the workpiece, the tool holder 48a and the control sleeve 72a are displaced by the spring element 74a in the percussion direction 56a such that openings 76a of the control sleeve 72a become positioned over the idling openings 70a, and release through-passages. A pressure in the air cushion 66a between the piston 62a and the striker 54a can escape through the idling openings 70a. In an idling operating mode (FIG. 1), the striker 54a is not accelerated, or is accelerated only slightly, by the air cushion 66a. In an idling operating mode, the striker 54a does not exert any percussion impulses, or exerts only slight percussion impulses, upon the striking pin 58a. The rotary and percussion hammer 12a has a hand power-tool housing 78a, having a handle 80a and an ancillary handle 82a, by which it is guided by the user.
(21) The control unit 14a has a load estimator 18a. The load estimator 18a is integrated into the control unit 14a. The control unit 14a is provided to identify an operating state of the percussion mechanism 16a. The control unit 14a is provided to process at least one operating parameter. The control unit 14a is provided to process the operating parameter as a function of at least one known load and of at least one load to be estimated. The load estimator 18a of the control unit 14a is provided to estimate an unknown drive load .sub.L, using a measured motor rotational speed of the motor 36a. The unknown drive load .sub.L is an unknown load moment M.sub.L acting upon the motor 36a.
(22) A total moment M denotes the sum of all moments acting on the motor 36a. M comprises a drive moment of the motor M.sub.M and the unknown load moment M.sub.L. J is the rotational inertia of all parts of the motor 36a, transmission unit 38a and eccentric gear mechanism 46a that rotate with , wherein the transmission ratios must be taken into account. The following principle of angular momentum then applies:
(23)
(24) The total moment M is the sum of a moment M.sub.M of the motor 36a and of moments M.sub.Li of loads acting upon the motor 36a:
(25)
(26) The motor rotational speed can be represented as a function of time (t), which is composed of a basic rotational speed .sub.0 that does not change, or that changes only slowly, and of rapidly changing, highly dynamic components .sub.i(t), and of the sought drive load .sub.L:
(t)=.sub.0+.sub.1(t)+.sub.2(t)+ . . . +.sub.L
(27) The functions .sub.i(t) describe known loads. This equation is obtained by integration of the principle of angular momentum, and consequently the functions do not have the dimension of a torque and are therefore denoted by the letter instead of M. The procedure is known to persons skilled in the art. The load to be estimated .sub.L can be obtained by subtracting the known quantities from the measured motor rotational speed (t). In this case, .sub.M(t) is the function of the moment M.sub.M of the motor 36a:
.sub.L=(t).sub.0.sub.M(t).sub.1(t).sub.2(t) . . .
(28) The known load components .sub.i(t) describe, in particular, rotational speed fluctuations caused by variable transmission ratios, motor cyclic irregularities and an irregular voltage supply, e.g. by an activation of the motor. A distinction may be made between time-periodic loads .sub.i(t) and angle-periodic loads .sub.i(). A time-periodic load .sub.i(t) may be, for example, a voltage fluctuation, in particular having double the grid frequency of an electric power supply to the rotary and percussion hammer 12a, and an angle-periodic load .sub.i() may be, for example, a transmission ratio that changes with a rotary position of the eccentric gear mechanism 46a. Loads whose characteristic is known precisely will be stored as a computational rule on the control unit 14a by persons skilled in the art.
(29) The control unit 14a is provided to identify the operating state of the percussion mechanism 16a. FIG. 3 shows a sequence diagram of the control unit 14a during operation of the percussion mechanism 16a. An input is the measured motor rotational speed . In a first step 94a, a sensor compensation may be effected, depending on a sensor used. In a further step 96a, a mean rotational speed is determined from the measured motor rotational speed . In a further step 98a, a difference of the measured motor rotational speed and the mean rotational speed is determined. Time-periodic loads .sub.i(t) are subtracted in a subsequent step 100a, and angle-periodic loads .sub.i() are subtracted in a subsequent step 102a. Optionally, influencing quantities 84a calculated from further input quantities may be subtracted in a step 104a. The result is the characteristic of the load to be estimated .sub.L, which may be further analyzed and/or filtered in a further step 106a. In particular, patterns may be processed, in particular a periodicity having an expected percussion frequency. The estimated load is output as a load quantity 86a. The operating state is determined by comparison of the load quantity 86a with a limit value. By means of this comparison, the control unit 14a can determine the operating state of the percussion mechanism 16a, in particular the percussion operating mode and the idling operating mode.
(30) FIG. 4 shows a representation of a sequence diagram of the control unit in a learning mode, for the determination of known loads. The measured motor rotational speed is calculated as a function of time t (time domain) (t) based on time, and as a function of an angle (angle domain) () based on angle. In an angle domain, it is possible to identify, in particular, periodic influences that are dependent on the rotary position of the eccentric gear mechanism 46a and/or of the motor 36a. In a step 108a, (t) is determined over a period t.sub.1 from .sub.1(t). The result is the learned characteristic of the known load .sub.1(t). In a step 110a, () is determined over the periods .sub.2 from .sub.2() and, in a step 112a, over the period .sub.3 from .sub.3(). The result is the learned characteristics of the known loads .sub.2() and .sub.3(). The periods on an angle basis are dependent on transmission ratios of the influences causing these loads to the motor rotational speed . Depending on the number of angle-periodic loads and time-periodic load components taken into account, these are determined from the measured motor rotational speed in the manner described. Persons skilled in the art will appropriately define the number of loads .sub.i to be learned. A greater number i increases the accuracy of determination of the load to be estimated .sub.L, and increases the effort required for calculating and defining and/or learning the loads. Advantageously, learning occurs in the idling mode, without influence of the load to be estimated .sub.L. The determination of the known loads .sub.i in the learning mode is explained further in the following FIGS. 5 and 6.
(31) FIG. 5 shows a representation of parameters that influence the measured motor rotational speed . The parameters are the loads .sub.i (t), .sub.2() and .sub.3(). The lowermost diagram 174a shows the characteristic of the measured motor rotational speed (t) in the time domain, which includes the influence of loads .sub.i. The diagrams 176a, 178a, 180a, from the bottom upward, show characteristics of two angle-periodic loads .sub.2() and .sub.3() with a differing period and a time-periodic load .sub.1(t). The topmost diagram 182a shows the characteristic of the basic rotational speed .sub.0. The basic rotational speed .sub.0 remains unchanged over a relatively long period, and may assume a new value upon a change of operating mode. The basic rotational speed .sub.0 corresponds, for example, to a rotational speed setpoint value of the motor 36a for a desired percussion frequency.
(32) FIG. 6 shows a representation of the characteristics of parameters learned in the learning mode. The learned parameters are the learned characteristics of the loads .sub.1(t), .sub.2 () and .sub.3(). The topmost diagram 184a shows the measured motor rotational speed (t) in the time domain. Shown beneath are learned characteristics of the loads .sub.1(t), .sub.2() and .sub.3(), in diagram 186a by averaging over the period t.sub.1 from .sub.1(t), in diagram 188a by averaging over the period .sub.2 from .sub.2(), and in diagram 190a by averaging over the period .sub.3 from .sub.3(). In the present example, the period .sub.3 from .sub.3() is one revolution of the motor 36a, and the period .sub.2 from .sub.2 () is one revolution of the eccentric gear mechanism 46a.
(33) The control unit 14a is provided to set at least one operating parameter temporarily to a start value 28a, in at least one operating state, for the purpose of changing from the idling operating mode to the percussion operating mode. The start value 28a may be, in particular, a percussion frequency at which a reliable percussion mechanism start is possible.
(34) FIG. 7 shows a percussion energy E as a function of the frequency f and a possible definition of the start value 28a, a limit frequency 128a, a working frequency 130a and a maximum frequency 132a of the percussion frequency of the percussion mechanism 16a. In the case of a change of operating mode to the percussion mode, a reliable percussion mechanism start occurs below the limit frequency 128a. If, in the percussion operating mode, the percussion frequency, starting from a value below the limit frequency 128a, is increased into the range between the limit frequency 128a and the maximum frequency 132a, the percussion mechanism remains in the percussion operating mode as the percussion energy E increases. Above the limit frequency 128a, a change from the idling operating mode to the percussion operating mode does not occur, or occurs only in few cases; starting from the idling operating mode, the striker 54a cannot follow, or can scarcely follow, the movement of the piston 62a. Above the maximum frequency 132a, a percussion operating mode terminates in most cases. For the percussion operating mode, a working frequency 130a can be set after a percussion mechanism start has been effected, and the performance capability of the percussion mechanism 16a can thus be increased, as compared with operation below the limit frequency 128a. A percussion frequency or percussion mechanism rotational speed 124a above this maximum frequency 132a is not usable. The percussion mechanism rotational speed 124a in this case corresponds to the rotational speed of the eccentric gear mechanism 46a, and thus to the percussion frequency. Optionally, an idling value 90a may be defined for the idling operating mode, which idling value is advantageously higher than the start value 28a and lower than the working frequency 130a.
(35) A mode change sensor 34a is provided to signal a change of the operating mode. The mode change sensor 34a transmits a signal 92a (FIG. 8) to the control unit 14a when the control sleeve 72a is displaced, such that the idling openings 70a are closed and the percussion mechanism 14a changes from the idling mode to the percussion mode. In particular, if a percussion frequency is selected that is higher than a start value 28a at which a reliable percussion mechanism start is possible, the control unit 14a first reduces the percussion frequency to the start value 28a. If the change from the idling operating mode to the percussion operating mode is identified by means of the load estimator 18a, the control unit 14a sets the percussion frequency to the selected percussion frequency.
(36) FIG. 8 shows a sequence diagram of the operation of the percussion mechanism unit 10a. The diagram 166a shows the signal 92a of the mode change sensor 34a, wherein the value 1 signals the percussion mode. The percussion mechanism 16a is changed from the idling mode to the percussion mode if the mode change sensor 34a signals the change of the operating mode. The diagram 170a shows a setpoint value of the percussion-mechanism rotational speed 124a corresponding to the percussion frequency. The percussion-mechanism rotational speed 124a and the motor rotational speed (t) are used as equivalents here; for specific numerical values, it is necessary to take account of a transmission ratio between the motor 36a and the eccentric gear mechanism 46a. In the case of the percussion mode being identified, the setpoint value of the percussion-mechanism rotational speed 124a is lowered to the start value 28a. The diagram 168a shows a signal 88a of the load estimator 18a, wherein the value 1 signals the percussion operating mode. As soon as the percussion operating mode commences, the setpoint value of the percussion-mechanism rotational speed 124a is raised to the percussion-mechanism rotational speed 124a that corresponds to the working frequency 130a, wherein a delay parameter determines a slope of the rise. The percussion operating mode is then maintained until the mode change sensor 34a signals the change to the idling mode. The motor rotational speed (t) is represented in the lowermost diagram 172a.
(37) The following description and the drawings of further exemplary embodiments are limited substantially to the differences between the exemplary embodiments and, in principle, reference may also be made to the drawings and/or the description of the other exemplary embodiments in respect of components having the same designation, in particular in respect of components having the same reference numerals. To differentiate the exemplary embodiments, the letters b, c and d have been appended to the references of the further exemplary embodiments, instead of the letter a of the first exemplary embodiment.
(38) FIG. 9 shows a representation of signal spectra of a rotary and percussion hammer, not represented in greater detail here. The rotary and percussion hammer comprises a percussion mechanism unit, in a second exemplary embodiment that differs from the preceding exemplary embodiment in that a load estimator includes a filter unit, which is realized as a bandpass filter. The bandpass filter suppresses components of a rotational speed signal outside of a known frequency band excited by a percussion frequency. The percussion frequency corresponds to a rotational speed of an eccentric gear mechanism that drives a piston of a percussion mechanism. The percussion frequency excites oscillations having the percussion frequency itself, and/or oscillations having a multiple of the percussion frequency. A suitable frequency band that can be passed by the bandpass filter therefore lies in the range of the percussion frequency or a multiple of the percussion frequency. Depending on user settings, the percussion frequency lies in a range of 15 Hz-70 Hz. In FIG. 9, a percussion frequency of 40 Hz has been set. This frequency is not visible in the signal spectrum 156b during percussion operation. In the case of the rotary and percussion hammer of the second exemplary embodiment, a clear maximum 162b, having five times the percussion frequency, at 200 Hz, is clearly visible in the signal spectrum 156b. This is almost entirely absent in the signal spectrum 158b in the idling operating mode. In this exemplary embodiment, therefore, a mid-frequency 164b of a frequency response 160b of the bandpass filter is fixed to 5 times the percussion frequency. In the case of adjustment of the percussion frequency, or of the rotational speed of the eccentric gear mechanism, the mid-frequency 164b is altered accordingly. The clear maximum 162b in the case of five times the percussion frequency in the percussion operating mode is suitable for determining an operating state of the percussion mechanism, in particular an idling operating mode and the percussion operating mode. If a signal, present at an output of the bandpass filter, that has been filtered by the bandpass filter exceeds a defined threshold value, the percussion operating mode is identified. The threshold value, the mid-frequency 164b and a bandwidth of the bandpass filter will be appropriately defined in trials by persons skilled in the art. In the exemplary embodiment, the threshold value can be set by means of an operating element, not represented in greater detail.
(39) FIG. 10 shows a rotary and percussion hammer 12c having a percussion mechanism unit 10c, having a control unit 14c and a percussion mechanism 16c, in a third exemplary embodiment. The percussion mechanism unit 10c differs from the first exemplary embodiment in that a load estimator 18c is realized as a load observer 20c. The load observer 20c has a dynamic model, which is provided to estimate a load moment {circumflex over (M)}.sub.L of a motor 36c of a drive unit 30c (FIG. 10). The load observer 20c determines the load moment M.sub.L from a motor rotational speed and a motor current i of the motor 36c of the drive unit 30c (FIG. 11). FIG. 12 shows a system comprising the load observer 20c and the drive unit 30c operated with a voltage U. By means of a simulation element 122c of the dynamic model and the correcting element 192c, the load observer 20c uses the motor current i and the motor rotational speed to estimate the load moment {circumflex over (M)}.sub.L. The basis of the load observer 20c is a model of the motor 36c, as a basis of the estimation algorithm:
(40)
(41) In this case, J.sub.M is the moment of inertia of the motor 36c, is the motor rotational speed of the motor 36c, c is the flux-dependent motor constant, is the linked flux, M.sub.L is the load moment acting on the motor 36c, e is a constant frictional component, a is a viscous frictional component and b.sup.2 is a turbulent frictional component.
(42) FIG. 13 shows a characteristic curve c()i=c(i) of a flux-dependent motor constant for determination of the drive moment M.sub.M as a function of the motor current i. The drive moment M.sub.M is the moment that exerts a magnetic field, caused by the motor current i, upon the motor 36c. This characteristic curve may be determined by means of a finite-element model of the motor 36c, or by another method considered appropriate by persons skilled in the art. In the case of a direct-current motor, the motor constant is constant, and not dependent on , such that this relationship is simplified.
(43) It is assumed that a load moment M.sub.L changes only slowly with time, i.e. that the following applies approximately:
(44)
(45) The load observer 20c is realized as a Luenberger observer, known to persons skilled in the art, in which the motor rotational speed of the motor 36c estimated by the simulation element 122c of the dynamic model is compared with the actual rotational speed. In the following equation of a dynamics of the load observer, in which the constant frictional component and the turbulent frictional component have been disregarded, the estimated states are denoted by {circumflex over ()}, {circumflex over (M)}:
(46)
l.sub.1 and l.sub.2 represent correcting element 192c of the load observer 20c. Through appropriate selection of the coefficients l.sub.1 and l.sub.2, it is possible to influence the observer dynamics of the observer, i.e. the speed with which the estimated motor rotational speed {circumflex over ()} converges with the measured motor rotational speed in the case of a deviation. Persons skilled in the art will select a suitable observer dynamics to enable identification of an influence of the part of the load moment M.sub.L that is caused by an operating state to be identified. It is advantageous to select an observer dynamics that corresponds at least to the duration of a movement cycle of a piston 62c and/or of a percussion cycle of a striker 54c of the percussion mechanism 16c. The load moment {circumflex over (M)}.sub.L estimated by the load observer 20c corresponds in this case to a mean value of a load moment M.sub.L present at the motor 36c during a percussion cycle. This mean value is influenced substantially by a piston movement, and differs significantly in a percussion operating mode and in an idling operating mode of the percussion mechanism 16c.
(47) Techniques for determining the coefficients l.sub.1 and l.sub.2 for designing the observer dynamics are known to persons skilled in the art. If the load moment {circumflex over (M)}.sub.L exceeds a threshold value, a percussion operating mode can be identified. Moreover, a characteristic of the load moment {circumflex over (M)}.sub.L is recorded by the control unit 14c. A service state of the rotary and percussion hammer 12c can be deduced from a long-term trend of the load moment {circumflex over (M)}.sub.L. A rise in the mean load moment {circumflex over (M)}.sub.L, in particular in the idling operating mode, is an indication of increasing internal friction of the rotary and percussion hammer 12c. This is an indication of dirt accumulation, inadequate lubrication or further wear phenomena. A recommended service of the rotary and percussion hammer 12c is signalled to a user by a service light, not represented in greater detail here, as soon as a limit value of the mean load moment {circumflex over (M)}.sub.L is exceeded and/or the mean load moment {circumflex over (M)}.sub.L rises sharply in a time period. In the exemplary embodiment, a recommended service is signalled if, in the idling operating mode, the mean load moment {circumflex over (M)}.sub.L is more than 50% higher than a reference value.
(48) FIG. 14 shows, exemplarily, the characteristic of the actual load moment M.sub.L and of a load moment {circumflex over (M)}.sub.L estimated by the load observer 20c. The load observer 20c is implemented, advantageously, on the control unit 14c. The estimated load moment {circumflex over (M)}.sub.L may be used on the control unit 14c as an input quantity of a control loop algorithm, for example for closed-loop control of the motor 36c. In the percussion operating mode, the load moment {circumflex over (M)}.sub.L rises as a result of a periodically changing air pressure of an air spring between the striker 54c and the piston 62c, such that the air pressure can be estimated using the load moment {circumflex over (M)}.sub.L. A control loop algorithm of the motor 36c can thus take account of the air pressure of the air spring. The period corresponds to the percussion frequency and to the rotational speed of an eccentric gear mechanism 46c. There is no need for measurement of the load moment M.sub.L. Advantageously, the load observer 20c is implemented in a time-discrete form, for the purpose of calculation, on a digital signal processor of the control unit 14c. The transformation of the equations is effected by a Tustin approximation (bilinear approximation), known to persons skilled in the art.
(49) The operating state is determined by a comparison of the estimated load with at least one limit value 26c. The upper diagram 114c of FIG. 15 shows a characteristic of the load moment M.sub.L, the middle diagram 116c shows a characteristic of the load moment {circumflex over (M)}.sub.L estimated by the load observer 20c, and the lower diagram 118c shows a signal 92c representing the operating state, wherein a value of 1 corresponds to the operating state percussion operating mode, and a value of 0 corresponds to the operating state idling operating mode. The observer dynamics has been selected such that the estimated load moment {circumflex over (M)}.sub.L converges during the duration of a percussion cycle, such that the estimated load moment {circumflex over (M)}.sub.L corresponds to a smoothed estimated load moment {circumflex over (M)}.sub.L. The limit value 26c is set such that, in the case of a comparison of the estimated load moment {circumflex over (M)}.sub.L with the limit value 26c, the estimated load moment {circumflex over (M)}.sub.L in the percussion operating mode is greater than the limit value 26c, and in the idling operating mode is less than the limit value 26c. In the example, the limit value 26c is half the mean estimated load moment {circumflex over (M)}.sub.L in the percussion operating mode. As a result of the smoothing of the estimated load moment {circumflex over (M)}.sub.L, owing to the selected observer dynamics, the estimated load moment {circumflex over (M)}.sub.L remains continuously above the limit value 26c during the percussion operating mode. The control unit 14c furthermore includes a protective circuit, which switches off the drive unit 30c of the percussion mechanism 16c on account of overload if a maximum value 126c of the estimated load moment {circumflex over (M)}.sub.L is exceeded.
(50) FIG. 16 and FIG. 17 show a percussion mechanism unit 10d for a rotary and percussion hammer 12d in a further exemplary embodiment. The percussion mechanism unit 10d differs from the preceding percussion mechanism unit in that an operating parameter defined by a control unit 14d is a throttle characteristic quantity of a venting unit 32d. A percussion space in a hammer tube 42d is delimited by a striking pin and a striker. The venting unit 32d has venting openings in the hammer tube 42d for venting the percussion space. The venting unit 32d serves to balance the pressure of the percussion space with an environment of a percussion mechanism 16d. The venting unit 32d has a setting unit 136d. The setting unit 136d is provided to influence venting of the percussion space, disposed in front of the striker in a percussion direction 56d, during a percussion operation. The hammer tube 42d of the percussion mechanism 16d is mounted in a transmission housing 138d of the rotary and percussion hammer 12d. The transmission housing 138d has ribs 140d, which are disposed in a star configuration and face toward an outside of the hammer tube 42d. Pressed in between the hammer tube 42d and the transmission housing 138d, in an end region 144d that faces toward an eccentric gear mechanism, there is a bearing bush 142d, which supports the hammer tube 42d on the transmission housing 138d. The bearing bush 142d, together with the ribs 140d of the transmission housing 138d, forms air channels 146d, which are connected to the venting openings in the hammer tube 42d. The air channels 146d constitute a part of the venting unit 32d. The percussion space is connected, via the air channels 146d, to a transmission space 148d disposed behind the hammer tube 42d, against the percussion direction 56d. The air channels 146d constitute throttle points 150d, which influence a flow cross section of the connection of the percussion space to the transmission space 148d. The setting unit 136d is provided to set the flow cross section of the throttle points 150d. The air channels 146d constituting throttle points 150d constitute a transition between the percussion space and the transmission space 148d. A setting ring 194d has inwardly directed valve extensions 154d disposed in a star configuration. Depending on a rotary position of the setting ring 194d, the valve extensions 154d can fully or partially overlap the air channels 46d. The flow cross section can be set by adjustment of the setting ring 194d. The control unit 14d adjusts the setting ring 194d of the setting unit 136d by rotating the setting ring 194d by means of a servo drive 120d. If the venting unit 32d is partially closed, the pressure in the percussion space that is produced upon a movement of the striker in the percussion direction 56d can escape only slowly. A counter-pressure forms, directed against the movement of the striker in the percussion direction 56d. This counter-pressure assists a return movement of the striker, against the percussion direction 56d, and thereby assists a percussion mechanism start. If the value selected for the percussion-mechanism rotational speed is an above-critical working value at which a reliable percussion mechanism start is not possible with the venting unit 32d open, the control unit 14d partially closes the venting unit 32d, for the purpose of changing from the idling operating mode to the percussion operating mode. Starting of the percussion operating mode is assisted by the counter-pressure in the percussion space. After the percussion mechanism has been started, the control unit 14d opens the venting unit 32d again. The control unit 14d can also use the operating parameter of the throttle characteristic quantity of the venting unit 32d for the purpose of regulating output.
