EP3554765B1 - Control method for an impact handheld machine tool - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to control methods for a percussive power tool, in particular a hand-held pneumatic hammer drill and a hand-held pneumatic electric chisel.

DE 10 2012 208870 A1 discloses a control method according to the preamble of claim 1.

The hammer mechanism of a rotary hammer heats up during operation due to the friction of moving components and thermal losses in the air spring. Typically, the operating temperature is between 80 °C and 150 °C. Lubrication, seals, dimensions and tolerances of the impact mechanism are designed with regard to the typical operating temperature. However, at the beginning of the commissioning, the impact mechanism is cold, especially in cold working environments below freezing. The conditions are not optimal for the impact mechanism and can prevent the impact mechanism from starting reliably.

DISCLOSURE OF THE INVENTION

A control method according to the invention for a percussive handheld power tool according to claim 1 has the steps: detecting a switching state of an operating button, detecting a temperature with a temperature sensor, activating an electro-pneumatic impact mechanism in response to the operating button being actuated, with an exciter of the electro-pneumatic impact mechanism moving along a The working axis is moved back and forth at a repetition rate R, which moves a beater coupled to the exciter via a pneumatic chamber. If the temperature is greater than a limit temperature, the repetition rate is continuously increased from rest to a setpoint. A number of exciter cycles until the target value is reached is less than 10 cycles. If the temperature is less than the limit temperature, a number of cycles of the exciter to reach the setpoint is greater than 200 cycles.

In a preferred embodiment, if the temperature is greater than the limit temperature, the repetition rate is continuously increased with a first acceleration. Otherwise, if the temperature is lower than the limit temperature, in a first phase a Driven intermediate value, the repetition rate is increased at least in sections with the first acceleration, and in a second phase, the repetition rate with a second acceleration up to the setpoint continuously increased. The second acceleration can be less than 1/10 of the first acceleration.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

einen Bohrhammer

Fig. 2

ein Steuerungsdiagram

Fig. 3

eine Repetitionsrate nach dem Einschalten des Bohrhammers

Fig. 4

eine Repetitionsrate nach dem Einschalten des Bohrhammers

Fig. 5

ein Steuerungsdiagram

Fig. 6

eine Repetitionsrate nach dem Einschalten des Bohrhammers

Fig. 7

eine Repetitionsrate nach dem Einschalten des Bohrhammers

The following description explains the invention using exemplary embodiments and figures. In the figures show:

1

a hammer drill

2

a control chart

3

a repetition rate after turning on the hammer drill

4

a repetition rate after turning on the hammer drill

figure 5

a control chart

6

a repetition rate after turning on the hammer drill

7

a repetition rate after turning on the hammer drill

Elements that are the same or have the same function are indicated by the same reference symbols in the figures, unless otherwise stated.

EMBODIMENTS OF THE INVENTION

1 shows a hammer drill 1 as an example of a percussive hand-held machine tool. The rotary hammer 1 has a tool holder 2, in which a drill, chisel or other striking tool 4 can be used and locked coaxially to a working axis 3 . The hammer drill 1 has a pneumatic impact mechanism 5 which can periodically strike the tool 4 in an impact direction 6 . A rotary drive 7 can continuously rotate the tool holder 2 about the working axis 3 . The pneumatic percussion mechanism 5 and the rotary drive are driven by an electric motor 8 , which is fed with electricity from a battery 9 or a mains line.

The hammer mechanism 5 and the rotary drive 7 are arranged in a machine housing 10 . A handle 11 is typically arranged on a side of the machine housing 10 facing away from the tool holder 2 . The user can use the handle 11 to hold and guide the rotary hammer 1 during operation. An additional auxiliary handle can be attached near the tool holder 2 . On or near the handle 11 is a Operating button 12 arranged, which the user can preferably operate with the holding hand. The electric motor 8 is switched on by pressing the operating button 12 . Typically, the electric motor 8 rotates as long as the operating button 12 is held down.

The pneumatic hammer mechanism 5 has an exciter 13, a hammer 14 and optionally a die 15 along the direction of impact 6. The exciter 13 is forced to move periodically along the working axis 3 by means of the electric motor 8 . The beater 14 couples to the movement of the exciter 13 via an air spring. The air spring is formed by a closed pneumatic chamber 16 between the exciter 13 and the beater 14 . The bat 14 moves in the direction of impact 6 until the bat 14 hits the die 15 . The die 15 rests against the tool 4 in the impact direction 6 and transfers the impact to the tool 4.

The exemplary percussion mechanism 5 has a piston-shaped exciter 13 and a piston-shaped hammer 14 which are guided along the working axis 3 through a guide tube 17 . The exciter 13 and the beater 14 bear against the inner surface of the guide tube 17 with their lateral surfaces. The pneumatic chamber 16 is closed off by the exciter 13 and the beater 14 along the working axis 3 and by the guide tube 17 in the radial direction. Sealing rings in the lateral surfaces of the exciter 13 and the beater 14 can improve the airtight closure of the pneumatic chamber 16 .

The exciter 13 is connected to the electric motor 8 via a transmission component. The gear component transfers the rotational movement of the electric motor 8 into a periodic translational movement along the working axis 3. An exemplary gear component is based on an eccentric wheel 18 which is connected to the electric motor 8 . A connecting rod 19 connects the eccentric wheel 18 to the exciter 13. The exciter 13 moves synchronously with the electric motor 8. The electric motor 8 typically rotates in response to the operation button 12 being pressed and continues to rotate as long as the user keeps the operation button 12 pressed. The periodic forward and backward movement of the exciter 13 also begins and ends when the operating button 12 is actuated or released. Another example of such a transmission component is a wobble drive.

The exciter 13 moves at a repetition rate R which is proportional to the speed of the electric motor 8 . The transmission components between the electric motor 8 and the exciter 13 typically have a step-down effect in a fixed ratio. The repetition rate R is in the range, for example, between 30 cycles per second (Hz) and 150 Hz. During operation, the beater 14 is coupled to the exciter 13 by the pneumatic chamber 16 and moves at the same repetition rate as the exciter 13. The beater 14 is coupled to the exciter 13 exclusively via an air spring. The air spring is based on a pressure difference between the pressure in the pneumatic chamber 16 and the pressure in the environment. The positively moved exciter 13 increases or decreases the pressure in the pneumatic chamber 16 by means of its periodic axial movement. The hammer 14 is accelerated by the pressure difference in the direction of impact 6 or counter to the direction of impact 6 .

The hammer drill 1 has a device control 20 which specifies the repetition rate R of the exciter 13 . The device controller 20 controls the electric motor 8 . For example, the electric motor 8 contains a speed controller, for which a target value for the speed is specified by the device controller 20 . Speed control can also be implemented in the implement controller 20 based on a speed sensor on the motor shaft and a negative feedback loop. Alternatively, the device controller 20 can limit a power consumption of the percussion mechanism 5 or a power consumption of the electric motor 8 in order to specify the repetition rate.

The device controller 20 detects the position of the operating button 12. The operating button 12 has an off position, to which the device controller 20 responds by specifying a repetition rate of zero, ie the percussion mechanism 5 switches off. The operating button 12 has an on position, to which the device control 20 activates the percussion mechanism 5 in response. The electric motor 8 is accelerated up to a nominal value in order to obtain a specified target repetition rate 21 of the exciter 13 . Preferably, the operation button 12 will automatically return from the on position to the off position if the operation button 12 is not held down.

The repetition rate R is increased when the operating button 12 changes from the off position to the on position depending on a temperature T of the rotary hammer 1. A temperature sensor 22 in the machine housing 10 measures the current operating temperature T. The temperature sensor 22 can be attached to the hammer mechanism 5 or together with other electronics of the device control 20 can be arranged on a printed circuit board.

2 shows an example control scheme of the device controller 20. 3 shows the behavior of the repetition rate R for different temperatures. The repetition rate is plotted against the ordinate in FIG. time is plotted against the abscissa. The user presses the operating button 12. The operating button 12 changes from the off position to the or one of the on positions. The device controller 20 detects the depressed position at time t2 (S1). The striking mechanism 5 is now activated.

The device controller 20 detects the temperature T from the temperature sensor 22 and compares the temperature T with a limit temperature Tc (S2). The limit temperature Tc is e.g. below 10°C, e.g. at 10°C, 5°C, 0°C, -5°C, -10°C. The limit temperature Tc can be set, inter alia, depending on the lubricating oil used in the hammer mechanism 5 .

Suppose the temperature T is above the limit temperature Tc. The exciter 13 starts to move back and forth. The exciter 13 is indirectly accelerated (S3), in the example by the electric motor 8. The repetition rate R increases up to the setpoint repetition rate 21. When the target repetition rate 21 is reached, the hammer drill 1 is fully operational and the switching-on process is complete. The target repetition rate R is specified for a percussion mechanism 5 and typically the efficiency or the percussion power of the percussion mechanism 5 is highest at the repetition rate R. Typical target repetition rates of hand-held hammer drills range between 30 cycles per second (Hz) for larger hammer mechanisms and 150 Hz for smaller hammer mechanisms. The further behavior of the rotary hammer 1 depends on the application and the use by the user (S5). The course of the repetition rate R is in 3 shown dashed.

The target repetition rate R is preferably reached as quickly as possible. A power consumption P of the percussion mechanism 5, in this example the power consumption of the driving electric motor 8, is preferably not limited by a control or regulation. The exciter 13 and the electric motor 8 accelerate with the maximum characteristic values Pmax of the rotary hammer 1. The target repetition rate R is reached, for example, in a duration t1 of preferably less than 1 s, e.g. less than 0.5 s, less than 0.2 s . The Schlagwerk 5 is fully operational in less than 10 cycles.

Suppose the temperature T is below the limit temperature Tc. The switch-on process is now divided into two phases. During the first phase, the exciter 13 is accelerated to a repetition rate with a temperature-dependent intermediate value RTc. The intermediate value RTc is above 20%, eg above 40%, 60%, below 80%, eg below 70% of the target repetition rate 21. The intermediate value RTc can decrease as the temperature T increases. For example, the intermediate value RTc2 for -10 °C is lower than the intermediate value RT1c for -5 °C. The intermediate values RTc are larger as the minimum repetition rate from which, at least at room temperature (20° C.), the racket 14 can follow the movement of the exciter 13 . The racket 14 is already beginning to follow the movement of the exciter 13 . Due to the low repetition rate R , the deflection of the racquet 14 is still low and the impact energy is correspondingly low. The intermediate value RTc is preferably reached as quickly as possible. A power consumption P of the percussion mechanism 5, in this example the power consumption of the driving electric motor 8, is preferably not limited by a control or regulation. The exciter 13 and the electric motor 8 accelerate with the maximum characteristic values Pmax of the rotary hammer 1 (S6). The intermediate value RTc is reached, for example, in a period of preferably less than 1 s, for example less than 0.5 s, less than 0.2 s.

After reaching the intermediate value RTc (S7) , the second phase begins. During the second phase, the power consumption P of the percussion mechanism 5 is reduced to a lower value PTc (S8). The acceleration of the exciter 13 is significantly lower in the second phase than in the first phase. Acceleration can be less than a factor of ten. The exciter 13 can require more than 5 s, for example more than 10 s, until the target repetition rate 21 is reached. According to the invention, the exciter 13 only reaches the desired repetition rate 21 after 200 cycles, for example after 500 cycles. The user clearly perceives the change in the switch-on process. The course of the repetition rate R is in 3 shown as a solid line for two different temperatures.

When the setpoint repetition rate R (S9) is reached, the switch-on process is complete and operation (S5) begins.

A variation of the switch-on process is in 4 shown. The process is essentially as to 2 described. The hammer drill 1 has a vibration sensor 23. During the slow acceleration, ie with the limited power consumption PTc, the device control 20 checks whether the vibration values exceed a vibration limit value. Provided that the vibration levels do not exceed the vibration limit, the control method is no different from 2 . If the vibration limit is exceeded, for example at time t3, the acceleration of the exciter 13 is increased. The exciter 13 can be accelerated up to the target repetition rate 21 with the maximum acceleration, ie unlimited power consumption Pmax . The switch-on process can be shortened as a result.

figure 5 shows an example control scheme of the device controller 20. 6 shows the behavior of the repetition rate R for different temperatures. The repetition rate is in plotted against the ordinate; time is plotted against the abscissa. The user presses the operating button 12. The operating button 12 changes from the off position to the or one of the on positions. The device controller 20 detects the depressed position at time t2 (S1). The striking mechanism 5 is now activated.

The device controller 20 detects the temperature T from the temperature sensor 22 and compares the temperature T with a limit temperature Tc (S2). The limit temperature Tc is, for example, below 10°C, for example at 10°C, 5°C, 0°C, -5°C, -10°C. The limit temperature Tc can be set, inter alia, depending on the lubricating oil used in the hammer mechanism 5 .

Suppose the temperature T is above the limit temperature Tc. The behavior is the same as in the methods described above. The exciter 13 is accelerated as quickly as possible to the target repetition rate R (S3). When the target repetition rate 21 (S4) is reached, the rotary hammer 1 is fully operational and the switching-on process is complete. The further behavior of the rotary hammer 1 depends on the application and the use by the user (S5). The course of the repetition rate R is in 6 shown dashed.

Suppose the temperature T is below the limit temperature Tc. The switch-on process is divided into two phases.

During the first phase, the exciter 13 is accelerated to the maximum (S10). The power consumption P of the percussion mechanism 5 is not limited. The exciter 13 is accelerated until it reaches a preset value Ro . The default value Ro is in the range between 80% and 150% of the target repetition rate 21. The default value Ro is temperature-independent. Because of the maximum acceleration, the default value Ro is reached, for example, in a period of preferably less than 1 s, for example less than 0.5 s, less than 0.2 s. Although the exciter 13 is moved, no movement of the racquet 14 is to be expected. Subsequently, the exciter 13 is moved for a predetermined holding time with the set value Ro (S12). For example, until the time tw after switching on has passed. The holding time can be between 2 s and 20 s. The holding time is preferably temperature dependent. The holding time decreases with increasing temperature T. 6 shows the behavior for a temperature at -5°C (dotted) and at -10°C (solid).

Following the hold time, the repetition rate R is reduced. The repetition rate R is reduced to the temperature-dependent intermediate value RTc . For example, the Power consumption P are set to zero (S13), whereby the percussion mechanism 5 expires and rapidly slows down. Alternatively, the power consumption P can be reduced to such an extent that the power consumption no longer compensates for friction losses and thermal losses. Furthermore, the impact mechanism 5 can also be actively braked. Reduction of the repetition rate R is terminated when the intermediate value RTc is reached. The intermediate value RTc can be chosen in the same way as in the previous examples.

The first phase is followed by the second phase, which proceeds in the same way as in the previous examples. For example, the power consumption P is increased to a temperature-dependent value PTc (S8). The exciter 13 is continuously accelerated until the target repetition rate 21 is reached (S9). Then the switch-on process is complete.

The hammer drill 1 can have a vibration sensor 23 . The device controller 20 checks in a variant of the method of figure 5 while reducing the repetition rate R (S13/S14), whether vibrations exceed a vibration threshold. Provided that the vibration limit is not exceeded, the procedure runs as in figure 5 shown. 7 illustrates this behavior in the solid line. If the vibration limit value is exceeded, the reduction in the repetition rate R is terminated prematurely before the temperature-dependent intermediate value RTc is reached. The exciter 13 is immediately accelerated to the target repetition rate 21 according to the second phase, ie steps S8 and S9 .

Claims (10)

1. Control method for an impact hand-held power tool (1), having the steps of

   sensing a switched state of an operating switch (12),

   sensing a temperature (T) with a temperature sensor (22),

   activating an electro-pneumatic impact mechanism (5) that responds to actuation of the operating switch (12), wherein an exciter (13) of the electro-pneumatic impact mechanism (5) is moved back and forth along a working axis (3) with a repetition rate (R), with the result that a striker (14) coupled to the exciter (13) via a pneumatic chamber (16) is entrained,

   characterized in that,

   when the temperature (T) is higher than a limit temperature (Tc), the repetition rate (R) is increased continuously from rest up to a setpoint value (21) and a number of cycles of the exciter (13) until the setpoint value (21) is reached is fewer than 10 cycles, and in that, when the temperature (T) is lower than the limit temperature (Tc), a number of cycles of the exciter (13) from rest until the setpoint value (21) is reached is more than 200 cycles.
2. Control method according to Claim 1, characterized in that, when the temperature (T) is higher than the limit temperature (Tc), the repetition rate (R) is increased continuously with a first acceleration, and when the temperature (T) is lower than the limit temperature (Tc), in a first phase an intermediate value (RTc) is headed for, wherein the repetition rate (R) is increased at least progressively with the first acceleration, and in a second phase, the repetition rate (R) is increased continuously with a second acceleration up to the setpoint value (21).
3. Control method according to Claim 2, characterized in that the second acceleration is less than 1/10 of the first acceleration.
4. Control method according to Claim 2 or 3, characterized in that, in the first phase, the repetition rate (R) is increased continuously from rest, with the first acceleration, up to the intermediate value (RTc), and subsequently, in the second phase, the repetition rate (R) is increased continuously with the second acceleration up to the setpoint value (21).
5. Control method according to Claim 1 or 3, characterized in that, in the first phase, the repetition rate (R) is increased from rest with the first acceleration up to a preset value (Ro) and the repetition rate (R) is lowered, starting from the preset value (Ro), to the intermediate value (RTc), and subsequently, in the second phase, the repetition rate (R) is increased continuously with the second acceleration up to the setpoint value (21).
6. Control method according to Claim 5, characterized in that the preset value (Ro) is between 80% and 150% of the setpoint value (21).
7. Control method according to one of the preceding Claims 2 to 6, characterized in that the intermediate value (RTc) is set depending on the temperature (T).
8. Control method according to one of the preceding Claims 2 to 7, characterized in that, for the first acceleration, the impact mechanism (5) is accelerated with a maximum power consumption (Pmax).
9. Control method according to one of the preceding Claims 2 to 8, characterized in that the temperature-dependent intermediate value (RTc) is between 20% and 80% of the setpoint value (21).
10. Control method according to one of the preceding Claims 2 to 9, characterized in that the setpoint value (21) is between 30 cycles per second and 150 cycles per second.

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