DE2855217A1 - Penetration depth control for electric hand drill - measuring change in time of reflected sound wave from pulse generator - Google Patents

Abstract

An electrically powered hand held drill is fitted with a sound wave device for measuring the depth of the hole being drilled. The device consists of a pulse generator which emits a sound wave at regular intervals. The reflected sound wave is received by a sensor. The time interval between emission and return of a particular pulse is compared with the time interval which occurs when the correct depth of hole has been drilled. When the correct depth has been achieved the drill is automatically switched off.

Description

El ektrowerkz eug

Processing of all kinds of workpieces as well as stone and concrete walls means designed for the operations of drilling, hammer drilling or hammer drilling Power tools is always linked in some way with the problem, drilling to be introduced from at least some precisely defined depth. To this end mechanical depth stops are used, provided that the prerequisites for this are met in the form of longitudinal bars ver # yendct, usually in one at the neck of the in question coming power tool elbringbaren handle are held longitudinally displaceable.

Such depth stops are considering the in question coming drill lengths to be measured relatively very long and therefore bulky and often annoying. There is also the risk that the clamping screw for the loosens the relevant depth stop as a result of vibrations from the power tool, so that the depth stop may be when it hits the workpiece Slides backwards imperceptibly so that the hole in question is too deep. There is also the risk that the depth stop and / or the handle will be misplaced will.

It is the object of the invention to provide a device for adjusting the Penetration depth of the drill into the workpiece to be machined for sheet metal tools for drilling, hammer drilling and impact drilling operations in which the disadvantages of mechanical stop elements avoided. are and optimal operational safety is guaranteed.

This object is achieved according to the invention in that the device a sound:> ender and one that reflected the object to be worked on Receivers receiving acoustic signals and the sound transmitter during the working phase of the power tool via a triggered pulse Pulse generator pulses are fed and the time difference between the transmission each of a sound pulse and the reception of the reflected echo of this pulse is converted into a corresponding signal, and that that changes with increasing penetration depth of the tool in the object changing signals continuously with one of the intended The comparison signal representing the drilling depth can be compared and if they match of the actual value signal with the specified comparison or

Setpoint signal a switching process is triggered.

It has proven to be particularly useful to use the time difference between the transmission of a sound pulse and the reception of the reflected one This impulse echoes into a signal with a distance of å twice the object distance to convert the corresponding pulse width and the with increasing penetration depth of the Tool in the object in question decreasing pulse widths of this Signals continuously with a predetermined drilling depth or penetration depth of the tool to compare the subject-representing impulse, so that when occurring one Signal of the same pulse width or pawn as the comparison signal of the switching process is triggered.

According to a further idea of the invention, the time difference between the time at which a sound pulse is emitted and the input of the reflected echo of this pulse also into a signal with one of the double Objective distance corresponding to the amplitude are transformed and which deal with Increasing depth of penetration, changing amplitudes of these signals can be done with a the amplitude representing the desired drilling depth can be compared and when it occurs of a signal with an amplitude corresponding to the comparison amplitude, the switching process to be triggered.

The invention is illustrated below with the aid of an example Switching arrangement shown in principle in connection with an electric tool explained in the form of a hammer drill.

The figures show: FIG. 1 a side view of the impact drill, which with equipped with a sound transmitter and the associated receiver, immediately before Commissioning, FIG. 2 shows a partial view of the machine according to FIG Depth penetrated #ierkzeug, Fig. 3 a switching arrangement in which the time difference between the time the respective sound pulse was emitted and the time the reception of the reflected echo of this pulse in each case in a corresponding Pulse width or a corresponding pulse width spacing is implemented, Fig 4 shows a basic circuit of a drilling tool setting generator; FIG. 5 shows a circuit example of an pulse width discriminator, FIG. 6 shows an exemplary embodiment of one with transistors equipped bridge circuit.

The Schlagbolir machine illustrated by Figures 1 and 2 1 is equipped with a sound sensor 2.2 'and a receiver 3.3' for receiving the from Item 4, e.g. in the form of a concrete wall, is equipped with reflected acoustic impulses.

In the structural unit sound transmitter-sound receiver are expedient also the electrical and electronic components required for setting and evaluation Components housed, so that the prerequisite for removing or replacing the complete device for adjusting the depth of penetration of the tool into the object to be processed is available and under certain circumstances even the possibility exists, power tools can be retrofitted with such an arrangement for contactless Setting of the required drilling depth and automatic shutdown of the tool when the tool has the desired or specified depth in the object has achieved to equip.

The sound transmitter-sound receiver unit is on the gearbox housing 5 of the hammer drill 1 is preferably arranged to be removable. At the concrete wall 4 adjacent drill 6 is the distance e from the sound transmitter or from the sound receiver clearly defined to the wall. This distance becomes less in the same wet as the drill 6 penetrates the wall. If the drill has reached the depth s, then is the distance of the nor sound transmitter or sound receiver / e '= e - s. That is, e and e 'sinc the two limit values, llobei in the case of the object distance e 'the drill switches off automatically or at least a signal is triggered, that the operator notices that the intended drilling depth is reached.

The required transit time of the individual sound pulses from the transmitter to the Concrete wall and the transit time of the sound pulse reflected by the concrete wall to the receiver defined on the assumption that the speed of sound is the same and the same distance between the sound transmitter and sound receiver from the concrete wall double the distance between the concrete wall and the non-contact depth measuring device.

The object distance is now twice as close to the concrete wall Drill, so at the distance. e, the upper limit value, in the case of the penetration depth s of the drill in the concrete wall. the lower limit value e '= e- s. All between Distance values lying between these two limit values are thus used during the drilling process run through.

If you now assign the upper limit value (distance e) a double Object distance corresponding signal, for example in the form of a corresponding Width (length, duration) of an impulse, and on the other hand one gives one of the opposing eggs stand removal) in the case of the penetration depth s of the drill into the concrete wall (e '= e-s) If the pulse width is relatively smaller, then it approaches with increasing penetration depth of the drill in the concrete wall due to the decreasing time differences of the continuously sent to and reflected sound pulses decreasing pulse width or Pulse duration constant of the nominal pulse width assigned to the lower limit distance e '.

If the actual value pulse width and the setpoint pulse width finally match, so either the drive motor of the power tool is switched off automatically or at least one optical or acoustic signal triggered.

As can be seen from the schematic diagram according to FIG the transmitter 2 for example in a flultivibrator 7 generated pulses m at regular intervals Sequence and fed at the same time intervals. The one downstream from the transmitter Electro-acoustic converter 2 'then emits a corresponding acoustic sequence Impulses. These impulses are reflected after they hit the concrete wall 4 and come back to an acoustic-electrical converter 3 ', which has a corresponding Received signal generated, which is fed to the inlpfanger 3 and amplified in this and that is then fed to a signal generator S: in a corresponding waveform r which also receives the time pulse m. The one designed, for example, as a read flip-flop Signal generator 8 supplies an output signal z, the pulse width or duration of which in each case corresponds to the current double object distance (distance from the start of the pulse m until the reflected sound pulse r).

The pulse z representing the actual distance to the object arrives then to a pulse width discriminator 9, which also uses the timer pulse m and to which the pulse signal h is also supplied, which indicates the preselected drilling depth s and which is generated by a setting generator 10.

The signal that is used to switch off the drive motor and / or the Triggering of an acoustic and / or visual warning is required on The output of the pulse width discriminator 9 receives the double of the respective Object removal Representative signal z (pulse width) with the comparison or target signal h (pulse width) constantly compares to the rhythm of the signal rims.

The setting generator 10 generating the setpoint signal h, which also is triggered by the timer pulse m, contains, as Fig.4 shows, for example an adjustment potentiometer 11 and a capacitor 12, the capacity of which is expedient can also be changed. ~ The width of the signal pulse h is determined by the Resistance of potentiometer 11 resp.

an adjustment resistance determined. The setting potentiometer 11 or the setting resistor are accessible from the outside on or in the area of the according to the invention # adjusting device attached.

As long as the pulse width or duration of the distance signal z is still is greater than that of the comparison or setpoint signal h, is available at the output dc s of the pulse width discriminator 9 of the 7 # state 1-0. That means, for example a bridge circuit 13 connected to the output of this discriminator on the input side has the signal state 1-0.

This signal is an error signal in the present case and has to Consequence, for example, that the coil of a contactor or Relay 14 energized and thus also the supply line 15 to the drive motor 16 via the contact 17 remains closed. Instead of a contactor or relay, a contactless one can also be used Switches are used.

When the contactor coil is energized, the lead 18 is also to a lamp 19 and a buzzer 20 interrupted.

If the width of the pulses h and z is the same, a zero condition results. This means that the status 0-0 is present at the output of the pulse width discriminator 9, which is also present at the input of the bridge circuit 13. This has the consequence that the contactor 14 drops out and the drive motor 16 from the Feed line 15 separates. If there is only one contactor for triggering warning signals, then the lamp 19 lights up in the signal state 0-0 and the buzzer 20 responds.

If necessary, to adapt the signals h and z to certain Control circuits between the output of the pulse width discriminator 9 and the input the bridge 13 can also be provided with pulse stretching stages.

The pulse width discriminator 9 can also be designed so that at its output, in addition to the switching states 1-0 and 0-0, the switching state 0-1 can occur. This switching state, which occurs in the case of a smaller pulse width of the distance signal z would be set as that of the setpoint signal h either for a reversal of the direction of rotation.

of the drive motor can be made usable or the automatic shutdown # of the Activate drive motor if after the occurrence of the switching state 0-0 at the output of the pulse width discriminator 9, the drive motor is not automatically stopped is, but only a warning signal appears or sounds and the operator does not perceive this for some reason and therefore continues to drill. The non-automatic table shutdown of the drive motor after reaching the desired penetration depth of the drill and therefore only an optical and / or acoustic display of this State is always advantageous if there is a risk that the drill will be in the Workpiece gets stuck when the drive motor immediately after reaching the penetration depth of the drill switches off automatically.

If necessary, a switching device can also be provided, the alternative is an automatic shutdown of the drive motor or an acoustic one and / or visual signal display allows. Such a switching device is for example realizable in that the output of the measuring bridge 13 by means of a Changeover switch from contactor 14 separated and connected to another contactor that only opens the circuit for the lamp 19 and / or the Sumuer 20 and closes, but the motor supply line cannot interrupt.

The setting generator 10 according to Figure 4 receives the timing pulse m via the line 21. This pulse reaches a NOR gate 22, which is in the untriggered State holds an output s. In the case of triggering by the pulse of the signal m the output of the gate 22 receives the state ogr. This has the effect that the capacitor 12 is charged via the potentiometer or the collision resistance 11 will. When the capacitor 12 is charged, the amplifier 23 is energized.

This amplifier then delivers a pulse h with one through that time interval required for charging the capacitor. For the width of the signal pulse h, the value of the setting resistance is 11 authoritative. The setting resistor 11 is accessible from the outside and e.g. by means of a Adjusting wheel 24 adjustable.

The feedback 23 'from the output of the amplifier 23 to the input of the Gate 22 is used to keep this gate constantly in the active state, when the capacitor 12 charges.

The pulse width discriminator 9 shown in Figure 5 can be at his Both outputs assume three states, namely the states 1-0, 0-1 and 0-0. The latter condition describes the condition that the widths of the two Pulses z and h to be compared with one another are equal to one another. In this case is either the drive motor 16 if necessary with simultaneous warning signal shut down or there is only a warning signal.

The state 1-0 means that the width of the pulse z is greater than that of the comparison or setpoint pulse h, so that accordingly can be drilled further. In the case of the state 0-1 is the width of the pulse z less than the width of the pulse h. That would mean that already too deep has been drilled. Regarding this condition, reference can be made to those already mentioned Possibilities are pointed out.

The pulse width discriminator 9 receives the pulses z and <, that is the impulse representing the respective object distance and the comparison or setpoint pulse.

The NAND gate 25 of the discriminator receives a pulse z and at the same time a pulse h 'from the output of NAND gate 26.

The pulse h 'represents the inverted pulse h.

The NAND gate 25 responds to a logical summation of signals derived from the pulses z and h '.

The NAND gate 27 receives the signal pulses h and simultaneously the Signal pulses z ', which are inverted z pulses in NA ## gate 28. The NÄND gate 27 also refers to a logical summation of the pulses h and z ' derived impulses.

If the width of the pulses z and h is the same, appears on both Outputs of the discriminator the signal state 0, that is, the state 0-0. This State indicates that the desired drilling depth has been reached and prompts accordingly the switching operations already described.

In the case of one of the bridge circuit 13 according to FIG. 6 via the line 29 supplied signal are the base of transistor 30 and the transistor 31 excited via line 32.

The conduction state of these two thyristors causes the current of a voltage source 33 via the transistor 31 zu.einer connection terminal 34 of the contactor or relay 14 flows, the other terminal 35 of which via the transistor 30 to Earth lies.

Correspondingly, the coil of the contactor or relay 14 would be in the opposite direction Direction are traversed by a current when a signal on line 35 queuing amrde. In this case the base of transistors 37 and 38 would be energized, whereby these are in the conductive state and a current flow from the Spairnungsquelle 33 via the transistor 38 to the terminal 35 of the contactor or relay 14 and from the terminal 34 of which would cause via the transistor 37 to earth.

A current flow thus has the excitation of the coil of the contactor or relay 14, so that its armature picks up and the contact in the #otor circuit 17 closes. The drilling process now continues unhindered until the entrance the bridge 13 no longer has a signal (0-0) and accordingly no more current through the coil of the contactor or relay 14 flows. Therefore, its anchor drops and breaks the power supply line 15 to the drive motor 16 of the hammer drill. This is with it disconnected from the supply network.

Is only a warning signal as an indication of the target drilling depth reached desired, the power supply line 15 to the motor 16 remains closed and that As is also indicated in FIG. 1, contactor 14 comprises only one in this case Contact 39, the circuit for the light bulb when the contactor winding is de-energized 19 and the buzzer 20 closes as long as the switch 40 is operated. The desk 40, which is actuated by a pusher 41 against the force of the return spring 42, also starts the multivibrator 7. The resistors assigned to the base of the transistors serve to limit the current.

The activation of the device for automatic adjustment of the drilling depth or to automatically switch off the drive motor of the relevant power tool and / or to give a warning signal after reaching the preselected drilling depth can for example by means of an on and off switch 43 on the power supply unit 44 (cf. also Fig. 15.

In order to have the opportunity to make the adjustment device ineffective make and the power tool, i.e. the hammer drill in the exemplary embodiment, To be able to operate independently of the device according to the invention is a bypass switch 45 provided. When this switch is operated, the setting device is switched on automatically prevented by an electrical locking system.

Distance measurement by means of sound waves, preferably at an ultrasonic frequency can also take place in that the sound waves, for example by means of a sawtooth generator be mudled in such a way that their frequency increases steadily and then back to the Initial value decreases.

The reflected sound waves arrive based on the emitted Sound waves with a time delay to the receiver 3'3, which is the greater, the the distance between the concrete wall 4 and the transmitter 2, 2 'is greater. As a result of the sawtooth-shaped The reflected sound waves have a lower frequency than that of modulation emitted waves.

The difference in the number of vibrations emitted by the transmitter 2, 2 ' Sound waves and the number of oscillations of the reflected waves reaching the receiver 3,3 ' Sound waves then each represent a point for the current depth of penetration Drill into the concrete wall. After reaching (actual value) one of the preselected Drilling depth (nominal value) corresponding difference value between the transmitted and Fn sound vibrations are then those already described several times Switching processes triggered.

Blank page

Claims (18)

P a t e n t a n t p r ü c h e 1. Power tool for drilling and / or Impact drilling and / or hammer drilling, which is done with a device to adjust the Penetration depth of the drill into the object to be machined or equipped is, characterized in that the device has a Schailender and a Receiver receiving acoustic signals reflected by the object to be processed and the sound transmitter during the working phase of the power tool pulses can be fed to a pulse generator started by a trigger pulse and the time difference between the emission of a sound pulse and the Reception of the reflected echo of this pulse is converted into a corresponding signal and that the penetration depth of the tool into the object decreases with increasing depth changing signals with a comparison signal representing the intended drilling depth are compared and if the actual value signal matches a predetermined one Setpoint signal a switching process is triggered. 2. Power tool according to claim 1, characterized gekennze2 c # et that the Time difference between the transmission of a sound pulse and the reception of the reflected echo of this pulse into a signal with one of the double Object distance is transformed into the corresponding pulse width and with increasing Penetration depth of the tool into the object with decreasing pulse widths these signals continuously with a pulse representing the predetermined drilling depth be compared and when a signal of the same pulse width or Duration of how the comparison signal triggers the switching process. 3. Power tool according to claim 1, characterized in that the Time difference between the transmission of a sound pulse and the reception of the reflected echo of this pulse into a signal with one of the do14 # eld # objects distance corresponding amplitude is reshaped and which decreases with decreasing Penetration depth changes the amplitudes of these signals with the desired drilling depth representing amplitude can be compared and when a signal occurs with a the amplitude corresponding to the comparison amplitude, the switching process is triggered. 4. Power tool according to claims 1-3, characterized thereby, that the switching process switches off the drive motor and / or an optical and / or acoustic signal. 5. Power tool according to claim 4, characterized in that at Agreement between the actual value and the setpoint signal in the supply circuit of the Drive motor lying switch is operated. 6. Elektrowerk ## eug according to claims 1-5, characterized in that that the pulse generator successive the pulses at the same time interval gives away. 7. Power tool according to claim 4, characterized in that the Pulse generator is embodied by an astable multivibrator. 8. Power tool according to claims 1-5, characterized thereby, that the trigger pulse for the pulse generator is started manually. 9. Power tool according to claim 6, characterized in that the Trigger pulse started when the power tool switch lever is pressed will. 10. Power tool according to one or more of the preceding claims, characterized in that the reflected pulses reaching the receiver possibly amplified and fed to a signal generator and as an actual value signal get to a pulse width discriminator. 11. Power tool according to claim 10, characterized in that the signal generator is designed as a read flip-flop. 12. Power tool according to one or more of the preceding claims, characterized in that a for specifying the comparison or setpoint signal The signal generator is used by an externally accessible actuator for changing is assigned to the pulse width of the signal and that this signal is a pulse width discriminator is fed. 13. Power tool according to An.C # n1ch 12, thereby kernel # zeicJrnet that the comparison of the respective nominal value impulses with the actual value impulses by means of a Pulse width discriminatory crs is done. 14. Power tool according to claim 13, characterized in that at. A bridge circuit is connected to the output of the Imy) ulsbreitendis1Lriminator is to which at least the signal states (1-0) and (0-0) are fed. 15. Power tool according to claim 14, characterized in that the signal state (0-0) the shutdown of the drive motor andfor a warning signal caused by a contactor or relay in the bridge output circuit. 16. Power tool according to claims 1-15, characterized in that that the setting device can be bypassed by a switch. 17. Power tool according to claim and one or more of the claims 4-9 and 16, characterized in that the frequency of the sound waves is generated by a sawtooth generator is modulated and the difference between the frequency of the emitted sound waves and the frequency of the reflected sound waves reaching the receiver is compared with a setpoint difference value, the drive motor switched off and / or a warning signal is triggered. 18. Power tool according to claims 1-17, characterized in that that the sound waves are ultra-frequency.