DE3027581A1 - Position control of speed regulated NC machine tool - has position and velocity loops to provide high speed positioning - Google Patents

Abstract

A high precision positioning servomechanism is for use on numerically controlled machine tools is designed to provide accurate control of the speed to achieve rapid positioning. The main spindle drive (1) of a milling machine is coupled (3) to the power gearbox (4) that transmits motion to the cutter (6). A digital position encoder (7) transmits pulses (11,12) to the position counter (13) that is coupled to a decoder (14) and digital to analogue converter (15). The generated analogue signal is fed to a position control amplifier (A) connected at speed regulating stages (23,24). A tachogenerator (2) provides velocity feedback and the spindle is moved at an optimised positioning rate.

Description

Method for positioning a speed-controlled machine part

The invention relates to the positioning of a speed-controlled Machine part according to the preamble of claim 1.

If it becomes necessary a machine part - that via a manual transmission driven in several, selectable speed ranges has a speed control - It is difficult to bring it into a predetermined standstill position as well to position the machine part quickly and precisely without annoying overshoot. Are switches such as limit switches, proximity switches, If a cam switch or similar is used, precise positioning is only possible if if the retraction takes place at a very low speed andZor several switching contacts or switching points are provided. If the machine part is often operated at high speeds drove; special precautions must be taken to ensure that the vehicle is driven through very frequently these switching points (even if no switching signals have to be given), no damage occurs or no wear occurs.

In particular with numerically controlled machine tools are such Provide the machine parts to be controlled with contactless position encoders of high resolution, The drive motor is controlled via their output signals after appropriate conversion will. However, precise positioning is possible with the known numerical controls only possible if the gear ratios of the individual stages of the gearbox not too far apart and the gearbox is a negligible one Has game. However, high performance must be transferred to the machine part and if this high performance is required in very different speed ranges, the gearbox must have gear ratios that are very far apart or the drive is so oversized7 that it can also be activated when it is activated Deliver a sufficiently high power to the machine part for low speeds can.

Such requirements can be used both for special machines in the printing or Textile industry as well as machine tools. So z. B. for the Spindle drive in machine tools for milling or spindles with high turning capacities required for the spindle in very widely spaced speed ranges, applied by a drive motor with powers between 5 and 100 kW and more and transmitted to the spindle via a gearbox. With such machine tools it may be necessary, e.g. for an automatic tool change or a Pulling the tool out of the workpiece, the spindle in its rotational position beforehand to position precisely. To make automation useful, positioning should be in each gear stage of the gearbox in the shortest possible time (e.g.

in approx. 1 to 3 seconds).

Such a positioning is only possible via a position encoder, which is connected as directly as possible (without play) to the machine part to be positioned is. However, this requires an activation of the control loops adapted to the position control loop, according to the different translation and different game of the individual gear stages of the gearbox. If you became a computer control for this (CNC), this is only possible with considerable effort, especially with the Programming and data storage, possible.

It is the object of the invention to provide a method and circuit arrangements indicate the very precise positioning with relatively little effort made possible, regardless of the selected stage of the gearbox. The invention, as it is characterized in the claims, solves this problem, with one High resolution position encoder enables fast and precise positioning.

In the following the invention is illustrated by means of one in the drawings Embodiment explained in more detail. It shows Fig. 1 the spindle drive for a Milling device with a circuit arrangement (block diagram) for its' control Fig. 2 and 3 positioning method based on spindle speed diagrams.

A spindle drive motor 1 with a tachometer generator 2 drives over a rigid coupling 3 and a power transmission 4, the spindle 5 for a milling tool 6, a digital position encoder 7 being provided at the output of the gearbox 4 is. It may be necessary for special work processes such as spindles (internal milling) the tool or workpiece with a precisely defined rotational position of the spindle 5 pull out. Even with an automatic tool change, an accurate Positioning of the spindle 5 is necessary if, as usual, on the shank 8 of the tool 6 sliding blocks 9 are provided, which are inserted into grooves with close tolerances on the spindle head Need to become. A problem-free use of a tool is often only here possible if the spindle is only slightly, e.g. not more than a tenth Degree deviates from a specified rotational position.

During normal machining of the workpiece, however, a precise speed control required, depending on the workpiece, workpiece material, Required surface quality, cutter radius, etc., very different spindle speed ranges Find application. Since the drive motor 1 has a high minimum power in all speed ranges must apply for the tool 6 and the motor 1 at a reduced speed The manual transmission is only able to provide a correspondingly lower performance 4 provided that by switching to different gear stages with appropriate Transmission ratios creates individual spindle speed ranges at their lower limit the speed of the drive 1 is still high enough to achieve the minimum output on the Transfer tool 6.

For example, with a five-stage power gearbox with gear ratios from l: loo, 1; 34, 1:11, 1: 3.4 and 1: 1, the following speed ranges are possible: Level 1: Spindle lo - 35 rpm Motor looo - 3500 rpm (1 / loo) Level 2: Spindle 30 - 105 "Motor 1020 - 3570" (1/34) Stage 3: Spindle 95 - 320 "Motor 1045 - 3520" (1 / 11) Level 4: Spindle 300 - 1050 "Motor la20 - 357o" (1 / 3.4) Level 5: Spindle looo - 3500 "Motor looo - 3500" (1/1) For this, the motor had to be designed in such a way that that he can still produce the minimum power at looo rpm.

In a machining center, the spindle 5 is only one of several axes to be controlled. These axes are usually controlled by a numerical control 1o and a power amplifier. This power booster can be provided with an additional device that the method according to the invention for positioning the spindle 5 possible. For this purpose, the position encoder 7 is designed in such a way that that he has a connection 11 high-resolution rotational direction-determinable pulses and Can give zero pulses to an up / down counter 13 via a line 12. Of the Position encoder 7 can be adjusted in such a way that the zero pulses are exactly in the rotational position in which the spindle is to be positioned. The zero pulses serve at the same time, with each spindle revolution, e.g. by setting to zero, to correct the values of the counter 13. The counter 13 is part of a position control loop with a decoding stage 14 and a digital-to-analog converter 15, which has a connection 16 an analog signal dependent on the zero position deviation to a position control loop amplifier 17 gives up. This position control loop amplifier 17 receives from a control logic 18 over the number of stages of the gearbox corresponding command lines 19, shift commands for control loop switching. The switching commands are made from one in the control logic Signal obtained, which is output via a connection 2o from the numerical control will that too. after. the present program via a connection 21 the manual transmission 4 toggles.

Depending on the pending command on the command lines 19, the position control loop amplifier 17 switched in such a way that the current transmission ratio of the manual transmission is balanced.

The output signal of the position control loop amplifier 17 can hereby by switching over independently of the gear stage that has just been switched of the gearbox 4, serve as a setpoint signal for a speed control loop, the depending on the output signal of the tachometer generator 2 designed here the current regulator 22 for the drive motor 1 controls.

As will be explained later, it can be more advantageous not to do this the speed control loop required for speed control during normal machining 23, but as shown in Fig. 1, an additional speed control loop 24. This control loop 24 receives the output signal of the position control loop amplifier via a line 25 17 and from tachometer generator 2 via line 26 the actual speed value signal and is an output signal to a controller switching stage 27, which according to a switching signal, that. She receives via a line 28 from the control logic 18, either the output of the speed control loop 23 for the normal machining process or the output of the additional speed control loop 24 for positioning the spindle 5 via a line 29 connects to an input of the current regulator 22.

During the normal machining process, e.g. milling a workpiece with the milling tool 6, according to the present in the numerical control lo Program and the gear stage of the gearbox 4 preselected from it, a speed setpoint Specified via a connection 30 to the speed control loop 23. Simultaneously receives the control logic 18 from the numerical control lo via a connection 31 a Command for processing and switches the output signal via controller switching stage 27 of the speed controller 23 to the input of the current controller 22, which the drive motor 1 brings it to this setpoint speed ..

Is now e.g. after completion of a processing step and after removal of the milling tool 6 from the workpiece at a spindle speed n1 'according to FIG a point in time tl via the numerical control lo the control logic 18 via a Connection 32 a command for positioning for a subsequent tool change given, generates the control logic 18, according to the switched gear stage of the gearbox 4 a discrete speed setpoint, which is transmitted via the line 34 instead of the speed setpoint from the numerical control lo the speed control loop 23 is fed. This discrete speed setpoint can be selected in such a way that that there is a spindle speed at which a positioning over with certainty the position control loop 13, 14, 15, 17 possible within a full spindle revolution is. If the gearbox 4 is on a level with a small gear ratio (area with high spindle speeds), this often results in a discrete speed setpoint with a spindle speed n2 below the maximum speed, which at a point in time t2 is reached. By comparing the output voltage of the tachometer generator 2, which is also fed to the control logic 18 via the line 26, with the discrete Speed setpoint or via a signal from an additional stage for speed monitoring, a signal "speed reached" is generated, which the control logic 18 prompts with the next zero pulse of the position encoder 7, which is transmitted via a line 35 of the control logic 18 is supplied to form a switchover command, which via the line 28 the Controller switching stage 27 actuated, with the additional speed control loop 24 is switched. During this time until the arrival of the zero pulse at t3, which - depending on the rotational position of the spindle at time t2 - can be of different sizes, the spindle speed n2 specified by the discrete speed setpoint remains obtain. The position control loop 13, 14, 15, with which on the selected gear stage adapted position control loop amplifier 17, here continuously gives analog setpoint signals to the speed control loop 24, which, however, can only have an effect if the controller switching stage 26 switches to this speed control loop 24. The output voltage and control loop characteristic is selected in such a way that after switching to the additional speed control loop 24, a positioning of the spindle 5 at the end of a full revolution at time t4. The shutdown takes place here the Spindle, without overshoot, approximating to an exponential function.

The additional speed control loop 24 can be omitted if the output of the speed control loop 23 is connected directly to the current controller 22 and the Controller switching stage 27 each the lines 25 or 34 to the setpoint input of the speed control loop 23 switches.

In Fig. 2 positioning methods are shown in which the gearbox 4 is switched to levels for high spindle speeds. When switching on a gear stage for a range with low spindle speeds (high gear ratio), this generally results in an optimal theoretical spindle speed value n4 (Fig. 3) for short-term positioning, which is due to the gear ratio, is far above the maximum speed of the drive motor 1.

So you can only choose the highest possible spindle speed n5 (n5 9 n lllax Also a short-term deceleration after the arrival of the next zero pulse from the position controller 7 at time t7 only brings disadvantages.

For example, the spindle speed n5 would be 30 revolutions per minute can be braked to e.g. 6 revolutions per minute in fractions of a second, whereby the spindle only executes a small rotary movement, the rest of the rotation up to the correct position after a full revolution would then be at an initial speed of e.g. 6 Ulmin take more than 10 seconds.

To avoid this, the control logic receives 18 from the decoding stage via a connection 39 binary position value signals that they each with preset compares selected pre-switch-off values according to the switched gear stage.

After the next zero pulse has arrived at time t7 er-7 there is now no immediate short-term braking via position control circuit 13, 14, 15, 17, but this will only be drawn later when the for the switched Gear stage selected pre-switch-off value is reached. Essentially, conditionally due to the low spindle speed n2, must still be with a relatively long positioning time t. This time can be shortened further, if the speed n5 is possible via a correspondingly late pre-switch-off value is retained for a long time and after the pre-switch-off value has been reached - instead of an immediate one Controller switchover - short-term the speed control circuit 23 over line 33 is supplied with a speed setpoint value "zero" until one Time t6 at which the actual value from the tachometer generator 2 matches the setpoint from the position control loop is equivalent to. This can be brought about by a comparison stage 37 which provides an output voltage from the position control loop amplifier 17 with the output voltage from the tachometer generator 2 compares and, if they are equal, a signal via a line 38 to the control logic 18 there. Only when this signal is present in the control logic 18 does it give one Switching command to the controller switching stage 27. The actual positioning via the position control loop 13, 14, 15, 17 takes place shortly before the end position a low spindle speed, whereby the positioning time t is significantly reduced.

p2 There are other advantages here, such as a simpler one Adaptation of the output signal of the control loop amplifier 17 during the switchover, as deviations from the comparison in comparison level 37 are largely balanced out and the speed control loop 24 for a small speed range with small Speeds can be optimized much better than with the speed control loop 23 is possible, which is designed for the entire speed range of the drive motor 1 have to be. Switching over to optimization is likely to be more time-consuming in most applications than the use of an additional speed control loop 24, as shown in FIG Fig. 1 is shown.

The circuit arrangement according to FIG. 1 enables the positioning of the Spindle 5 in both directions of rotation, whereby as in the most common cases e.g. a tool change required, only one end position is approached.

This is mainly made possible by starting with a zero pulse of the position encoder after a full clockwise or counterclockwise rotation of the spindle to the end position is driven. Once the end position has been reached, a signal from the decoding stage 14 that arrives at the control logic via connection 40 are used to generate the numerical Control via line 41 to give the instruction "spindle positioned" to the e.g.

initiates a tool change. Depending on the system and task, When the end position is reached, the drive is switched off, or the position against influences be held from the outside via the drive motor.

Position accuracy can be achieved with appropriate optimization of the control loops + 1 increment of the high-resolution digital position encoder 7, whereby the Game of the gearbox 4 is fully compensated.

The positioning method according to the invention can also be used in other applications Find use in which the spindle 5 or a corresponding machine part, must be positioned in different positions. This can be done through appropriate Changes in the position control loop 13, 14, 15 via additional stages with presettable Counters, programmable memories, decade switches or similar steps Input of a presettable setpoint signal corresponding to a selectable end position take place in a way, as is done with numerically to be positioned axes with numerical controlled machine tools is common.

A simple expansion circuit results when the zero pulse from the position sensor 7 via the line 12 not to the counter 13 but to another is supplied from the outside via a connection 42 presettable counter 43. This Like the payer 13, the payer 43 receives the individual pulses from the position encoder 7 and is activated by these pulses are gradually reset after being enabled by a zero pulse.

Every time the counter reaches "zero", the counter gives 43 an impulse via a line 44 to the counter 13, which is there like the original Zero pulse is effective. The zero pulse can be used to set the counter in to reset the externally specified payment status. The presetting can e.g. manually using a decade switch or using the corresponding numerical steps Control lo take place in accordance with the program parts present there.

Summary: Procedure for positioning a speed-controlled Machine part.

With speed-controlled machine parts (5) the huber has a gearbox (4) Driven by a motor (1), the machine part may be required even without switching the gearbox in a given rotational position beforehand to position. In order to be able to position as precisely and quickly as possible this in several steps.

First, the machine part is set to a machine-dependent speed (n2, n5) and then, based on a zero signal from a digital position encoder (7) for the machine part (5), a speed-controlled shutdown of the machine part in the end position via a position control loop. Is the manual transmission (4) into a stage with a high transmission ratio for low partial machine speeds switched, the switchover takes place shortly before the to be positioned is reached End position after brief braking to a low rotational speed. That Positioning methods can be used with appropriately constructed machine tools, textile machines or printing machines Find application, with a control circuit with relatively little effort becomes possible.

Claims (8)

Claims 1. Method for positioning a speed-controlled Machine part, in particular the spindle of a machine tool, its speed Can be changed over wide areas with the help of a drive motor that has a Gearbox that drives the machine part equipped with a digital position encoder and the drive motor has a speed sensor for a speed control loop, characterized in that when a positioning command is present, the speed control loop (23) a dependent on the selected gear stage of the gearbox (4) a discrete speed setpoint signal is supplied which corresponds to a speed, in the case of a shutdown of the machine part (5) with less or a maximum of one revolution is possible, after reaching the corresponding setpoint speed (n2, n5) the speed setpoint signal switched off and by an output signal of a position control loop (13, 14, 15, 17) is replaced, based on a zero signal of the digital position encoder (7) a Speed control circuit (24) supplies setpoint signals that are dependent on the rotational position deviation the drive motor (1) for a given position value of the machine part (5) brake in a controlled manner until the machine part (5) reaches the specified position Has. 2. The method according to claim 1, characterized in that when positioning is switched to an additional speed control loop (24) and the shutdown of the discrete speed setpoint signal via the zero signal of the digital position encoder (7) takes place. 3. The method according to claim 2, characterized in that the switching off of the discrete speed setpoint signal based on the acquisition of a zero signal after a cut-off value preset according to the selected gear stage, from the position control loop (13, 14, 15, 17). 4. The method according to any one of claims 1 to 3, characterized in that that after switching off the discrete speed setpoint signal the speed control loop (23) a setpoint signal for the speed setpoint zero is supplied briefly, until the output signal from the position control circuit tal3, 14, 15, 17) is about the same Has size, such as the actual value signal derived from the signal of the speed sensor (7). 5. The method according to any one of claims 1 to 4, characterized in that that the position control loop (13, 14, 15, 17) to one of the selected gear stage of the gearbox (4) adapted control loop gain is switched. 6. The method according to any one of claims 1 to 5, characterized in; that the position encoder (7) is set or adjusted so that the delivery of the Zero signal from the position encoder (7) takes place in the desired target position and that Positioning of the machine part (5) with switching off the discrete speed setpoint signal starts with a zero signal and after a full revolution of the machine part (5) ends. 7. The method according to any one of claims 1 to 5, characterized that the position control loop (13, 14, 15, 17) corresponds to a selectable end position preset setpoint signal is supplied and the position control loop (13, 14, 15, 17) supplies an output signal that is dependent on the position deviation from this setpoint. 8. Circuit arrangement for a method according to one of the claims 1 to 7, characterized in that the position encoder (7) as a pulse generator with high Resolution and additional output of a zero signal per revolution is designed, the position control loop (13, 14, 15, 17) with these pulses in a known manner Counting stages (13) and a digital-to-analog converter (15) an analog one of the positional deviation provides dependent output signal, that of a control loop amplifier (17) is supplied, its amplification via signals for the selected gear stage of the gearbox (4) is switchable so that regardless of the selected Gear ratio almost the same control loop behavior for the control of the drive motor (1) results in 9 circuit arrangement according to claim 8 or for a Method according to one of Claims 1 to 6, characterized in that the output signal the position control loop (13, 14, 15, 17) an additional speed control loop (24) is fed, the output of which is connected to a controller switching stage (27), which controlled by a switching signal the additional speed control loop (24) instead of the speed control loop (23) for speed control of the machine part (5) to the input of the current regulator (22) for the drive motor (1) and the switching signal a comparison stage (37) is taken, which is the output signal of the position control loop Compare (13, 14, 15, 17) with the actual value signal of the rotary encoder (2), lo. Circuit arrangement for a method according to claim 7, characterized in that a presettable Counter or programmable memory is provided in which a selectable position value can be entered, the output signals of the position encoder (7) to an up / down counter (13) are fed to the position control loop (13, 14, 15, 17) and via a counter reading comparison a binary position error signal is formed with the selectable position value, which a digital-to-analog converter (15) is fed, the output signal via a switchable control loop amplifier (17) fed to a speed control loop (24) is.