CH669354A5 - - Google Patents

Description

DESCRIPTION

The invention relates to a device for automatically positioning a toothing or grooving tool in relation to an already existing toothing or grooving of a prefabricated workpiece, the toothing or grooving tool being arranged on a tool spindle which runs essentially transversely or obliquely to a workpiece spindle and by means of an actuator is adjustable in the direction of its axis and a pulse generator scanning its teeth is arranged on the circumference of the workpiece and a second pulse generator is arranged on the circumference of the workpiece spindle, the pulse sequences of the same frequency in an electronic circuit arrangement depending on their phase positions relative to one another an electrical control signal as a control variable for controlling the Actuator is derived.

In a known device of the generic type (DE-OS 2 744 562), the position of the tool and the workpiece are measured and deviations from the reference position are determined by a detection circuit. The deviations from the reference position between the workpiece and the tool are canceled by means of appropriate correction signals by an axial displacement of the tool or an additional rotary movement of the workpiece. For this purpose, a measuring transducer is provided which can be inserted between the tool and the workpiece while they are running and can be removed again from this measuring position. The sensor is a pneumatic device with two pairs of nozzles, each pair of nozzles comprising an adjustable reference nozzle and a measuring nozzle that can be aligned with the tool or the workpiece to generate a signal that corresponds to the differential pressure and is supplied to the detection circuit. In addition to the detection circuit, two logic circuits are required. One of these circuits is connected to circuit means which generate measuring pulses whose frequency is higher than the frequency of successive tooth or gear pitches. A first counter is connected to the output of this first circuit, which algebraically sums up the measurement pulses controlled by the circuit as a function of the output signals of the detection circuit. The second logic circuit forms the correction signals in the forward and reverse direction depending on the counting content of the counter, which is connected to the output of the first logic circuit. In addition, a second adjustable counter for the tool gaps is attached to the detection circuit2

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closed, which determines the number of tooth or gear divisions over which the measurement and averaging is to be carried out. The output of the second counter is connected to the input of the second logic circuit.

In addition to the complexity and the great amount of circuitry involved in the circuit arrangement required for evaluating the measuring pulses, the encoder must be swiveled out of its rest position between the workpiece and the tool for each newly clamped workpiece and brought back into its rest position after the setting operation has been carried out. This requires time that reduces the number of items. In addition, an additional control and drive device for pivoting the encoder is required. Finally, the pneumatic measuring and reference nozzles are only suitable for scanning a grinding worm with gaps without gaps, but not for scanning a worm-shaped hob, for example, because a hob has no self-contained worm gears, but only has milling teeth arranged on a worm line, the gaps of which would generate additional impulses that are not useful for the evaluation. This means that this known device can only function in conjunction with grinding screws.

In a known tooth flank grinding machine (Soviet copyright certificate No. 200 394) it is also known to provide inductive sensors for the purpose of automatically adjusting the grinding gear (s) to a tooth gap of a prefabricated gear workpiece, with which the position of the tool and workpiece can be determined . These encoders are connected to a phase meter, which in turn is connected via an electrical amplifier to a servomotor which effects the axial displacement of the grinding worms. Since the workpiece is switched into the electromagnetic circuit of the one inductive transmitter so that it serves as a rotor, while the stator is designed in the manner of tooth sectors, it is necessary that the gear wheels to be machined consist of a ferromagnetic material and that Tooth sectors of the encoder have a pitch that corresponds to the tooth pitch of the workpiece to be machined. This means that different encoders must be available for different tooth pitches.

The reference measurement must be carried out when the gear is stationary by adjusting the milling spindle sensor and adjusting the gear sensor in such a way that the location of the sensors is changed manually. This type of determination of the reference quantity or the implementation of the comparison is not only cumbersome, but also imprecise.

In another known device (DE-OS 3 314 793), the pre-toothed workpiece is fixed in its clamping position by means of a positioning finger so that its toothing position coincides with the one reference angular position of the tool running at its working speed. The workpiece is rotated at a point in time at which the tool runs through the reference angular position mentioned until it is synchronized with the tool in terms of speed and angular position. From the same time, the encoder pulses of the tool are counted in a computing unit and compared with the counted pulses of a workpiece pulse generator in order to control the workpiece drive with the comparison signal. The rotation angle deviation between the workpiece and the tool is only determined when the synchronism is reached and is then corrected by the workpiece drive. An axial displacement of the tool is not provided. This method is very time-consuming because the alignment of the tool to its zero index mark must always take place when the tool is at a standstill.

The invention has for its object to improve the device of the type described in such a way that it avoids the aforementioned disadvantages, that it works in a time-saving manner and is suitable both for machining the workpiece with a grinding worm and with a worm-shaped hob and that there is no need for local displacement or pivoting of the sensor or sensors and that it operates with a higher level of functional reliability and setting accuracy than the known device.

This task is solved by the fact that the pulse generators work electronically and are arranged in a fixed location, that the second pulse generator senses a pulse marking arranged on the tool spindle or rotating synchronously with it, and that the phase difference is temporal by means of the electronic circuit arrangement which is programmable and in particular a process computer the pulse sequences of the same frequency are determined and the control signal is determined by comparing them with a predetermined reference variable which corresponds to the exact positioning of the gear cutting or grooving tool.

The specified solution achieves a higher work performance. Once the reference size has been determined, no manual manipulations are required. Any measurement errors can be eliminated by averaging, and simple pulse generators of any type can be used in conjunction with a relatively simple and also programmable circuit arrangement, which ensure quick and exact determination of the manipulated variable and thus exact control of the servomotor.

Advantageous embodiments of the invention are characterized in the dependent claims.

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

1 shows the workpiece and tool arrangement of a gear hobbing machine in perspective with a block diagram of an electronic circuit arrangement,

2 in a schematic representation three pulse sequences arranged one below the other,

3 shows the engagement of a milling cutter tooth in a tooth gap of a pre-toothed workpiece in a reference measurement,

4, 5 and 6 different angular positions of a tooth gap of the pre-toothed workpiece with respect to the center of a milling cutter tooth.

The gear hobbing machine 1 partially shown in FIG. 1 has a horizontal workpiece spindle 3 in a vertical stand 2 and has a counter holder arm 4 with a counter holder 5. A cylindrical workpiece 6 is clamped into the workpiece spindle 3, which has a prefabricated toothing 7 and is supported by a counter-holder cone 8 on its free end face. A headstock 10 with a horizontal tool spindle 11 is arranged on a plate-like tool spindle head 9 in such a way that the tool spindle 11 is arranged below the axis 12 of the workpiece spindle 3 or below the workpiece 6 to be machined. The tool spindle head 9 can be moved up and down in the vertical direction, can be pivoted about a vertical axis 14 and can be fixed in various angular positions and can also be displaced in the direction of the axis 12 of the workpiece spindle 3 or the workpiece 6, drives which can be controlled separately in each case for the linear movements, are provided. On the side opposite the headstock 10 is the tool spindle head 9 with an additional La5

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gerbock 15 provided, the bearing 16 is arranged coaxially to the tool spindle 11 and is used for additional storage of a tool mandrel 17 which is clamped in the tool spindle 11 and carries a worm-shaped hobbing cutter 18 which is arranged on it in a rotationally fixed manner. The cutting teeth 19 of the hobbing cutter 18 provided with the counter profile for the final tooth shape of the toothing 7 are arranged in a helical manner in a known manner. A hob cutter 18 made of hard metal is used for the finishing or finishing of the prefabricated toothing of the subsequently hardened workpiece 6. In the headstock 10 is a stepper motor 20 which can be controlled in both directions of rotation, by means of which the tool spindle 11 can be displaced stepwise in both directions in the direction of its axis 13, the smallest step size being of the order of a hundredth of a millimeter or even less.

For reworking the prefabricated hardened toothing 7 in the so-called peeling-milling process, it is necessary to align the teeth 29 of the hobbing cutter 18, which come into engagement with the toothing 7, exactly with the tooth gaps of the toothing 7 in such a way that tooth profiles with exactly the same pitch when reworking the prefabricated toothing 7 arise.

For this purpose, in the vicinity of the circumference of the prefabricated toothing 7 of the workpiece 6, a first electronic pulse generator 24 is arranged in the form of a proximity switch, which scans the tooth heads of the toothing 7 while the workpiece 6 is rotating. In the vicinity of the circumference of a disk 21 fixedly attached to the tool spindle 11, a second electronic pulse generator 22 is also arranged in the form of a proximity switch, which scans a pulse marking 23 which has the shape of a radial incision on the circumference of the disk 21 while the tool spindle 11 is rotating located.

As is customary with such gear hobbing machines, the speed nz of the workpiece spindle 3 is in a specific relationship to the speed nf of the tool spindle 11. This speed ratio is determined by the number of teeth Z of the toothing 7 to be machined and the number of gears g of the hobbing cutter.

The following applies:

n = - = -,

z Z '

so that the pulse trains I and II or III generated by the two pulse generators 22 and 24 each have the same pulse repetition frequency: the pulse repetition frequency Tf of the pulses generated by the pulse generator 22 at a constant speed of the tool spindle 11 is thus equal to the pulse repetition frequency Tz of the pulses generated by the pulse generator 24 the toothing 7. In order to ensure this, the disk 21 must each have a number of pulse markings corresponding to the number of gears g of the milling cutter at uniform angular intervals.

The two pulse generators 22 and 24 are connected via electrical lines 25 and 26 to a microprocessor 27 which is part of an electronic circuit arrangement 28 which is shown as a block diagram in FIG. 1. This circuit arrangement 28 comprises an input unit 29 for controlling and programming the microprocessor 27, a power unit 30 as a connecting element between the microprocessor 27 and the stepping motor 20, and a connecting circuit 31 as a connecting element to the standard electronic equipment of the machine.

During operation, i.e. During the rotation of the workpiece 6 and the hobbing cutter 18, the pulse sequences I and II or III shown in FIG. 2 arise, consisting of the individual pulses If and Iz or IZD, the pulse intervals Tf and Tz of all pulse sequences I, II, III, assuming constant speeds, are the same size. This means that the period Tf is the same for the individual pulse sequences I, II and III at constant speeds. The pulses If of the pulse train I are generated by the pulse generator 22, while the pulses Iz and Izp are each generated by the pulse generator 24. Of course, the rectangular shape of the pulses shown is ensured in a known manner by corresponding electronic differential elements, which are connected downstream of the pulse generators 22 and 24.

For the sake of simplicity, the pulses If of the pulse sequence I are referred to below as milling cutter pulses and the pulses Iz or Izp of the pulse sequences II and III are referred to as gear wheel pulses.

The fact that in the present example the pulse length Tbf of the milling cutter pulses is smaller than the pulse length TZb of the gear wheel pulses Iz or Izp is essentially due to the fact that the peripheral speed of the pulse marking 23 is greater than the peripheral speed of the workpiece 6, which, however, is due to the measurement is explained in more detail below, has no influence.

In order to have a reference variable available for the later determination of a control or manipulated variable, it is first necessary to carry out a reference measurement with a series production of the pre-toothed workpieces 6 to be reworked. For this purpose, by manual control of the hobbing cutter 18 in relation to the toothing 7 of the clamped workpiece 6, the alignment of the milling cutter teeth 19 to the center of the tooth space of the toothing 7 according to FIG. Fig. 3 made. I.e. the milling cutter teeth 19 are brought into engagement with the toothing 7 without backlash. It is advisable to check this alignment several times before starting the electronic reference measurement.

The electronic reference measurement is then carried out with the machine running, i.e. with the hob 18 running and the workpiece 6 running in the predetermined speed ratio and with the circuit arrangement 28 switched on, which now receives the two pulse sequences I and II from the two pulse generators 22 and 24. It is switched on by the input unit 28. The microprocessor is now programmed so that the time interval Ti between the rising edge of a milling cutter pulse If and the rising edge of the gear pulse Iz immediately following it is measured, and a measurement of the pulse length TZb of the gear pulse Iz is also found instead of. The value determined for Tzb is arithmetically halved and added to the determined value Ti, which then gives the time value T <jr.

However, in order to have an absolute number or an absolute value available as a reference variable, the value Tdr is divided by the period Tf in a further process.

The resulting reference quantity Qr is stored in a memory of the microprocessor 27.

To ensure safety and to eliminate any measurement errors that could arise, for example, from metal chips or other contaminations, in particular on the scanned teeth of the toothing 7 or also on the pulse marking 23 and as a result of concentricity or pitch errors, this measurement is carried out several times, e.g. Done 32 times. The arithmetic mean is formed from the values determined for each measurement, which then finally gives the stored reference variable Qr.

This clamped workpiece 6 can then be machined in the manually adjusted axial position of the hobbing cutter 18 after this reference measurement has been carried out.

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After inserting a new workpiece 6 of the same series, the exact alignment of the milling cutter teeth 19 with the tooth gaps of the toothing 7 of the newly clamped workpiece 6 must then take place again, but this time automatically, before machining by the hobbing cutter 18. For this purpose, with the help of the two pulse trains I and III, the value Tam is first determined according to the rule in the same way as for the reference measurement, which in turn is then divided by the value Tf by the period of the pulse trains I or II and III becomes. The absolute value Qp obtained therefrom is then compared arithmetically in the microprocessor 27 by forming the difference with the already stored reference value Qr. The resulting difference value Dq is then used to control the stepper motor 20 in such a way that it is multiplied by the axial milling pitch tf, which is known and represents a fixed size, which was previously input into the microprocessor by the input unit 29 becomes. The control or manipulated variable Sp is obtained. This is converted by the microprocessor 27 into a corresponding number of stepping pulses, which are fed from the power unit 30 to the stepping motor 20 and thus used for the corresponding axial adjustment of the tool spindle 11 with the hobbing cutter 18. When the axial adjustment of the tool spindle 11 with the hobbing cutter 18 has taken place in accordance with the determined manipulated variable Sp, the exact alignment is accomplished and during the subsequent machining phase it is ensured that the reworked edge profile of the toothing 7 of the workpiece 6 in question has the greatest possible precision.

It is obvious that not only for the reference measurement, but also for the phase difference Tdm to be newly determined with each new workpiece 6, the measurement is repeated several times and e.g. is also performed 32 times to obtain Tdm as an arithmetic mean from these measurements.

It is also possible to exclude any resulting measurement values of T2 that are outside a specified tolerance limit from the utilization for averaging. As can be seen from Fig. 4, the maximum axial displacement of the tool spindle 11 or the hob 18 required for alignment can be half an axial pitch tf, with the possibility of this axial displacement to the left or to the right, i.e. in a positive or negative direction. In terms of programming, there is the possibility of manipulating this decision in such a way that after a certain number of axial displacements in one direction, a certain number of axial displacements take place in the opposite direction. For this purpose, the microprocessor 27 is provided with an additional counting device 21 ', which can be programmed accordingly.

5 and 6, there is also the possibility of programming the microprocessor 27 in such a way that the shortest paths in one direction or the other are selected for the alignment. In the starting position shown in Fig. 5 it can be seen that the alignment distance di is significantly smaller than the alignment distance di, i.e. that an axial adjustment of the hob 18 in the direction of arrow 32 to substantially shorter 669 354

can be done in the opposite direction. Accordingly, a device is provided in the circuit arrangement 28 which compares the determined phase difference T2 with half the value of tf, that is to say with the value of half the tooth pitch of the toothing 7 or half the axial pitch or pitch of the helical milling cutter 18 and, depending on whether a positive or negative difference value results from this comparison, generates a positive or negative manipulated variable Sp in the form of positive or negative pulses for the stepping motor 20. If it is assumed that, in the case of FIG. 5, the direction of adjustment of the arrow 32 by positive impulses, i. H. 6, where the alignment distance di is significantly greater than the alignment distance d2, the shortest alignment in the direction of arrow 33 would be the shortest adjustment path in the case of FIG. to achieve with negative impulses.

Since the measurement process or processes for determining the temporal phase difference between the two pulse sequences I and III to be compared with one another can readily take place during a movement phase of the tool spindle head 9, in which the hobbing cutter 18 is not in engagement with the workpiece 6, there is the additional one The advantage of a significant time saving. For example, there is the possibility that the manipulated variable Sp for aligning the hob 18 on the toothing 7 of a newly clamped workpiece 6 can be carried out in the time in which the tool spindle head 9 moves from the end position of the machining of the previous workpiece 6 to the starting position for machining the next workpiece.

In some cases, especially when the number of teeth of the toothing to be reworked is very high, or when working at high cutting speeds, it may be advisable to carry out the measurements in a prescribed optimum manner in order to determine the manipulated variable Sp in the prescribed manner Reduce size and bring it back to the required cutting speed only after the alignment has been carried out.

It is also easily possible to use the adjusting drive in the form of the stepping motor 20 outside of any alignment functions in a known manner for axially displacing the hob 18 in order to obtain new, not yet blunt cutting teeth of the hob 18 in relation to the workpieces to be machined or in to bring in relation to the workpiece spindle axis 12 in the working position. It is clear that after such an axial displacement of the tool spindle 11 with the hob 18, a reference measurement has to be carried out again, which can then be followed by the usual phase difference measurements described above for determining the manipulated variable Sp. In principle, with the device described it is e.g. it is also possible to mill an additional toothing of the same or different number of teeth on a pre-toothed workpiece, the teeth of which should have a specific angular position with respect to the teeth of the existing toothing, according to which the milling cutter is to be positioned. Instead of a toothing, a grooving of a workpiece consisting of one or more grooves running at equal angular intervals can also be used and scanned as a reference for the milling cutter positioning. In the case of different numbers of teeth of the toothing to be placed in relation to one another or in the case of multi-start milling cutters, it is also possible to use electronic frequency reducers or the like to achieve a uniform pulse frequency.

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2 sheets of drawings

Claims (10)

669 354 PATENT CLAIMS 1.Device on a machine tool (1) for automatically positioning a gear cutting or grooving tool in the form of a worm gear hobbing cutter (18) or a grinding worm in relation to an existing toothing (7) or grooving of a prefabricated workpiece (6), the toothing or Grooving tool is arranged on a tool spindle (11), which runs essentially transversely or obliquely to a workpiece spindle (3) and is adjustable in the direction of its axis by means of a servomotor (20), and on the circumference of the workpiece (6) a pulse generator scanning its teeth (24) and a second pulse generator (22) are arranged on the circumference of the tool spindle, from their pulse sequences (I, II, III) having the same frequency, an electrical control signal (Sp) as an actuating variable for control purposes in an electronic circuit arrangement (28) depending on their phase positions the servomotor (20) is derived, characterized in that d ass the pulse generators (22, 24) work electronically and are arranged in a fixed position so that the second pulse generator (22) scans a pulse marking (23) arranged on the tool spindle (11) or rotating synchronously with it and that by means of the electronic circuit arrangement (28), which is programmable, determines the temporal phase difference (Tdr, Tdm) of the frequency-identical pulse sequences (I II, III) and compares them with a predetermined reference variable (Qr), which corresponds to the exact positioning of the gear cutting or grooving tool (18), the control signal is determined. 2. Device according to claim 1, characterized in that the pulse generators (22, 24) consist of proximity switches and that the pulse marking (23) arranged on the tool spindle (11) or on the part rotating synchronously therewith consists of a radial incision. 3. Device according to claim 1 or 2, characterized in that to determine the phase difference (Tdr or Tdm) between the two pulse sequences (I and II, or I and III), several successive measurements are carried out and that for comparison with of the reference variable (Qr) used phase difference value (Qp) represents an arithmetic mean of the values mentioned. 4. The device according to claim 3, characterized in that for arithmetic averaging only measured values are calculated that lie within a predetermined tolerance range. 5. Apparatus according to claim 3 or 4, characterized in that in order to determine the phase difference (Tdr, Tdm) between the two pulse sequences (I and II, or I and III), the time interval between the starting edge of a tool spindle or milling cutter pulse (If) and the center of the immediately following gear pulse (Iz or Izp) of the workpiece (6) is used. 6. Device according to one of claims 1 to 5, characterized in that the reference variable (Qr) is the quotient from the phase difference (Tdm) determined in a reference measurement as dividend and the period (Tf) of the pulse sequence generated by the first pulse generator (22) ( If) is used as a divisor. 7. Device according to one of claims 1 to 6, characterized in that the control or manipulated variable (Sp) for the adjusting drive (20) of the tool spindle (11) from the difference of the reference variable (Qr) and that for each workpiece ( 6) in the same way determined actual size (Qp) on the one hand and the axial division (tf) of the hobbing cutter (18) on the other hand and the adjusting drive (20) in the form of a positive or negative voltage pulse of corresponding duration or in the form of a corresponding number of positive or negative Step switching pulses is supplied. 8. Device according to one of claims 1 to 7, characterized in that in order to determine the shortest alignment distance (di, d2), the respectively measured phase difference (T2) is subtracted from the period duration (Tf) stored as the measured value. 9. Device according to one of claims 1 to 8, characterized in that a presettable electronic counting device (27 ') is provided to determine the number of alignment shifts of the hob (18) in the same direction, which switches when a preset number is reached of the subsequent alignment shifts in the opposite direction. 10. The device according to claim 1, characterized in that the programmable, electronic circuit arrangement is a process computer (27).