DE1278126B - Arrangement for generating a signal indicating and / or controlling the position of a movable body relative to a fixed reference system - Google Patents

Description

Arrangement for generating a relative position of a movable body to a fixed reference system indicating and / or controlling signal.

The invention relates to an arrangement for producing a indicating the position of a moving body relative to a fixed reference system and / or controlling signal by means of an intensity field in which the intensity varies locally according to a periodic pattern, its position relative to the reference system depends on the body position, and by means of an Sensor device resting in the reference system with at least two electrical signals emitting sensors, the intensity values at such points of the spatial pattern determine where the phases of the pattern are different from each other.

There are devices known to the speed of a rotating Body, e.g. B. a wave to determine. At these facilities the frequency is the appearance of one or more marks provided on the rotating body determined on a stationary sensor or transducer, which when the Brands emits pulses, the frequency of which is measured and a measure of the speed represents. The impulse output can be based on mechanical, magnetic, capacitive, be generated inductively or photoelectrically.

Facilities are also known with which on the same principle the size of a linear movement of a body relative to a fixed frame of reference is determined. For this purpose z. B. the reference system several equidistant from each other arranged marks (tick marks) attached to the movable body by a Transmitter are scanned when the body moves past the graduation marks.

The distance of the body from a certain starting position or the distance traveled by the body can be determined by counting in these devices all delivered by the probe since the body was removed from the original position Determine impulses.

A removal or removal carried out in this way. Orientation of a body is the more precise, the narrower and more precise the scanned division is. It has therefore already been proposed to be very accurate and especially for that Measurement of small distances suitable divisions optically through the interference from grating lines of two superimposed optical grids.

Let the devices working with the counting of impulses a position determination only if the body actually traverses a distance to run otherwise no countable pulses are generated.

Should the determination of the position from the route traveled also then being possible when the body changes its direction of movement is a distinction the pulses emitted in one or the other direction of movement and the corresponding Addition or subtraction required.

Known institutions in which an illuminated reticle or an interference pattern are scanned photoelectrically two or three photocells that scan the pattern at a short distance from each other and continuously output mutually phase-shifted signals, whereby from the phase shift the direction of movement of the body is determined. Via appropriately operated flip-flops the counting pulses derived from one of the signals are either sent to the addition or fed to the subtraction channel of a counter. Through the use of DC amplifiers for the photocell signals it is ensured that such devices also at renewed body movement after a standstill to correctly resume their function. To eliminate disadvantages caused by changing the DC level thermal drift or aging of the components is also suggested instead of two photocells four, in pairs in a push-pull arrangement to use powered photocells.

The object on which the invention is based is to provide an arrangement to create with which the position of a movable body relative to a fixed reference system can be determined without the body having to travel through a measuring section, i.e. with the z. B. A determination of the body position is also possible when the body is initially has not yet performed any movement, and besides, only with difficulty and without high effort to compensate direct current circuits gets by.

An arrangement described at the outset for solving this problem is according to the invention characterized by the combination of the following features: a) a cyclically operating switching device, which the individual sensors in different Switches on areas of the switching cycle; b) one following the switching device Summing device in which a series of the successive output signals the individual sensor is formed; c) a phase comparison device which one of the relative phase position of an output signal of the summation device corresponding signal generated for the reference signal of the respective switching cycle.

With this arrangement, the relative position of the movable Body-dependent spatial phase of the intensity pattern through a signal with a corresponding the temporal phase. Their position in relation to the one target or starting position of the body representing the phase of a reference signal gives a measure of the distance of the body from the target or starting position. A determination of the position of the body is therefore possible even when the body does not follow a certain route moved. Because of the cyclical switching device for the individual sensors no DC-coupled circuits are necessary.

The phases of the intensity pattern at the points where means the probe the intensity values are determined must differ from each other, it is basically irrelevant by what amount. To be as simple as possible To achieve the formation of the arrangement, however, it is expedient to change the arrangement of the Choose the sensor so that the phase of the intensity pattern is at the measuring point of each individual sensor from that at the measuring point of the first sensor by 1 + X, 2 + B etc. periods of the pattern are different. Where n is the total number the sensor and A and B any whole numbers, which can also be zero. It however, it is possible that a sensor scans several points of the same phase.

The intensity field can be realized in different ways. It can be a magnetic or an electric field. For example is it possible to create a periodic magnetic pattern on a magnetic tape of suitable To hold the length and this together with the movable body on magnetic Move scanning heads past. It is also conceivable to use the standing electromagnetic To exploit waves in a waveguide or a field acoustic, thermal or to generate mechanical quantities.

The use of an illumination field that is preferred is through Photoelectric elements is scanned and expediently by means of two relative mutually movable optical grating is generated. This can be translucent Act grating, or one of the grids can be designed as a reflection grating. The interference pattern can be achieved by the slight inclination of the lines of one grating opposite that of the other grid or by a different grid division of the two grids can be achieved. It is particularly useful if a diffraction grating a number of subdivisions corresponding to the number of sensors or photocells having.

It can of course be used instead of the linear intensity pattern also act around a polar pattern, with the repeating periods at angular intervals are arranged around a pole. This arrangement is useful when the Position of a dividing head or a rotatable pointer is to be determined.

The cyclical activation of the individual sensors can be done in a known manner Way electronically by turning the sensors on and off, e.g. B. with With the help of square pulses, happen.

However, it is also possible to generate suitable square-wave pulses using the To modulate the output signals of the sensors so that the amplitudes of the pulses of depend on the output signals of the sensors.

If the proposed arrangement z. B. used on machine tools, which are controlled with the help of signals stored on magnetic tape are expedient also the square-wave signals on this tape that are used to switch on the sensors saved.

A simple and reliable switch-on can be carried out without a tape the sensor can achieve its output signal with the aid of a square wave generator in a delay circuit in mutually phase-shifted control signals for Electronic switches assigned to the individual sensors are transformed.

Advantageously, the output signal of the same square wave generator the reference signal used for phase comparison is also derived, since then the arrangement always correct regardless of frequency or phase shifts of the generator is working.

Since the reference signal is preferably phase modulable, which is easiest to realize when the signal of the square wave generator has a frequency several times higher than the reference signal, and also the control signals for the sensors it is advisable to have the same frequency as the reference signal, is a frequency divider between the square wave generator and the delay circuit switched on.

Basically, the arrangement works with two or even three Sensors. However, the use of four sensors is preferred, whereby the Measurement accuracy is increased and the delay circuit is particularly simple build up leaves, since the required phase shifts then 1800 and 900 respectively. In this case, the sensors are at equal time intervals one after the other and all switched on for the same duration, e.g. B. for the duration of a half or quarter switching cycle.

In another embodiment, the switching device switches at least two light sources generating the intensity field instead of the measuring sensors a.

The output signal representing the relative position of the body the phase comparison device can directly change one in a reset circuit the position arranged servo device are fed to the body in a to hold the target position specified by the reference signal.

The invention is described below with reference to schematic drawings explained in more detail using several exemplary embodiments. 1 shows a schematic Representation of the arrangement to explain the invention, FIG. 2 shows a pulse plan for the arrangement according to FIG. 1, F i g. 3 shows an alternatively usable circuit of a Part of the arrangement according to FIG. 1.

The arrangement according to the invention is applied by way of example described in a machine tool in which the position of a movable, not shown slide relative to the stationary, also not shown bed of the Machine is to be determined. A short diffraction grating 11 is in one to the direction of movement of the carriage parallel plane attached to the bed so that the indicated at 12 Grid lines run at right angles to the direction of movement of the slide. On the sledge is a long diffraction grating 13 at a short distance from the diffraction grating 11 and in attached to a plane parallel to this, so that when the carriage moves moves the long diffraction grating along the short diffraction grating. Both grids will be by means of a fixed lighting direction on the side of the short diffraction grating, which comprises a light source 14 and a converging lens 15, transilluminated, whereby on on the side of the long grating a repeating interference pattern of different, spatially distributed light intensities is visible, whose spatial position or phase position, based on a fixed point, according to the relative position of the grids and thus straighten the sledge. Such an arrangement of diffraction gratings is known.

The interference pattern has that shown in FIGS. 1 and 2 at 20, approximately sinusoidal spatial course. The pattern is made using four, in one Row of spaced-apart phototransistors 16 "seen" in sections, to which the light passes through four adjustable openings 17 and a cylindrical lens 18 got. The distances between the phototransistors correspond to a quarter of the Wavelength of the interference pattern. The openings 17 are used to adjust the individual phototransistors striking amounts of light, so that all of them, independently of individual differences in photosensitivity, the same effective Possess sensitivity.

There is a common external resistance for the four phototransistors 16 19 is provided to which they are in parallel in a manner to be described below repeating cycle one after the other are switched, each for equal fractions of the period of the switching cycle. The size of that fraction can in principle be freely chosen; in the present example the phototransistors each switched on for half a period. As the phototransistors the common external resistance 19 are connected in parallel, arises at this a signal having a component having the frequency of the switching signal and whose phase position depends on the spatial position of the interference pattern, d. H. after the relative position of the two diffraction gratings. The higher frequency components this signal are filtered out in the manner to be described below and the remaining signal is converted into a square wave signal, which is the represents final actual or position signal 21 and its phase position a measure for the position of the machine tool slide.

The phase position of the signal 21 is determined by phase comparison with a constant frequency, likewise rectangular setpoint signal 22 is determined, the corresponding a desired specific target position of the carriage is phase modulated. When comparing the position or actual signal 21 and the reference or setpoint signal 22, an error signal 23 is generated which has a direct current component whose Size of the phase difference between the signals 21 and 22 depends. The error signal can be used to display the slide position by means of an electrical measuring instrument serve or be fed to a servomotor 24, which a slide movement in the direction of the target position until the error signal has decreased to zero is.

If due to the fineness of the diffraction gratings 11 and 13 by a period of the error signal 23 represented carriage path for a proper If the servo system is too small, it can be extended by a factor by checking the position signal 21 and the setpoint signal 22 before the phase comparison dividing this factor.

Both a cyclic connection of the phototransistors 16 on the common external resistance 19 controlling signal and the setpoint signal derived from a signal generated by a multivibrator 31 operating at 10 kHz, which contains two transistors 32.

A 10 kHz square wave signal taken from the first of the transistors 32 is fed to a two-stage frequency divider 33, which converts the pulse frequencies in Ratio 5: 1 and 2: 1 reduced to 1 kHz. The signal arrives from there into a delay circuit 34, the four square wave signals of the same frequency of 500 Hz, of which the second, third and fourth signals are opposite to the first signal are 90, 180 and 2700 out of phase.

The circuit 34 includes two flip-flop circuits 71 and 72 as well an AND gate 73. The frequency divider 33 has two outputs, each with the same frequency Emit pulse series which are phase-shifted by 1800. An exit is directly connected to the input of the flip-flop circuit 71, which is divided into two Outputs anti-phase square signals to control the activation of the first and third phototransistor outputs. An output of the circuit 71 is with to the The input of the AND gate 73 is connected, the other input of which is that of the second output of the frequency divider originating pulses are fed, which also an input the flip-flop circuit 72 are fed, the second input to the output connected to the AND circuit. The flip-flop circuit 72 gives two antiphase Square-wave switch-on control signals for the other two phototransistors away. Since circuit 72 toggles when the input signal from the AND gate goes positive, so if impulses occur simultaneously at both inputs of this gate, what is only the case after the output of the circuit 71 connected to the gate has become positive and then a pulse is emitted by the divider 33, it is ensured that that the output signals of the flip-flop circuit 72 always correspond in time to the corresponding Output signals of the flip-flop circuit 71 follow, and, since the two output signals of counter 33 are out of phase by 1800, lag by 900.

The four control signals go to the bases of four in the emitter circuits of the phototransistors 16 lying switching transistors 35 and switch over them the individual phototransistors one after the other for the duration of a half-wave of the square-wave voltages to the resistor 19, whereby a signal 38 is generated at this, which is composed of four, composing successive and temporally overlapping components 37, each of which is the respective illuminance of the associated phototransistor is equivalent to.

The phototransistors 16 and the switching transistors 35 are below similar operating point conditions operated, so that there are unfavorable effects approximately compensate for any thermal drift. In the base circles of the Potentiometers arranged in phototransistors are used to adjust the dark currents.

The step-shaped signal composed of the components 37 38 is smoothed in an integrating circuit 40 and arrives as signal 39 without Direct current component at the input of a Schmitt trigger 41. This triggers each time at the zero crossing of the signal 39 and gives the square-wave position signal 21 from, which has the same frequency of 500Hz as the control signals, its However, the phase position is a measure of the relative position of the two diffraction gratings.

The smoothing of the signal 38, i. H. filtering out higher frequencies Components is useful in order to obtain a signal 39 which is a relatively large Component with the frequency that controls the activation of the phototransistors Contains signals or the setpoint signal 22, which enables a more precise phase comparison. It is important that the circuit used for this is one of the existing ones if possible Frequency independent phase shift causes. In addition to the specified integrating circuit 40 known RC or LC circuits designed as band-pass or low-pass filters can be used use.

The time course of signals 37, 38 and 39 is shown in FIG. 1 and 2 shown individually only for the sake of clarity. Indeed, the individual occurs Signals 37 only in each case individually in the collector circuits of the phototransistors 16 on, and the summation and integration process is combined in such a way that directly the Signal 39 is generated without it being possible to detect the signal 38 separately.

A triggers on the second transistor to form the setpoint signal 22 32 of the multivibrator 31 picked up square wave signal is a monostable multivibrator 43, which a corresponding pulse series via an OR circuit 45 and an AND circuit 46 outputs to a frequency divider 47. This conducts every ten input pulses a pulse to a flip-flop circuit48, each time a pulse arrives tilts and thereby generates the rectangular target signal 22, half of the period duration corresponds to the duration of ten of the pulses fed to the frequency divider 47.

The position signal 21 and the nominal signal 22 are thus square waves of the same frequency, between which a phase shift may occur, which look for any difference between the actual position of the slide of the machine tool and the position specified by the setpoint signal of the sledge.

The two signals 21 and 22 are sent to a flip-flop circuit 49 fed, which an output signal 23 depending on the phase difference between the signals 21 and 22 generated, which after appropriate amplification, as described, is fed to the servomotor.

For a change in the target position of the slide, the phase position must of the setpoint signal 22 can be changed. This is done in a simple manner by using the in the unit of time to the frequency divider 47 normally supplied pulses A pulse is added to advance the phase or on to delay the phase Pulse is taken. This depends on the direction in which the target position of the carriage is to be relocated, either clamp 51 or clamp 52 or, for a larger installation, several command pulses are supplied. The input of command impulses caused via the respective terminals 51 or 52 assigned, identical synchronization circuits, a flip-flop circuit 61, an AND circuit 62, a flip-flop circuit 63, an AND circuit 64 and an inverting circuit 65 include the insertion of an additional pulse at the OR circuit 45 or the suppression of a pulse at the AND circuit 46, with pulses from a to the multivibrator 31 connected toggle circuit 44 are used, which the have the same shape and frequency as those from circuit 43, compared to these but are out of phase by 1800.

Any other suitable circuitry can be used. For example, the setpoint signal from the four rectangular ones that control the activation of the phototransistors Generate signals that are applied to a potentiometer designed as a bridge circuit one of which is in the phase position of the wiper position of the potentiometer dependent voltage can be removed after filtering and square-wave shaping the signal 22 corresponds.

In some cases it is useful to use the inputs of the frequency divider 33 and 47 to be interchanged, so that now the control voltages for the Phototransistors are phase modulated and the resulting positional or the actual signal is compared with the setpoint signal 22, which is now phase-constant.

In a modified embodiment, to control the Phototransistors required square wave signals from an on magnetic tape recorded rectangular signal obtained. For this purpose, the magnetic tape is used in the usual Way scanned with a scanning head acting as a differentiator (Fig. 3), the responds to the edges of the recorded square wave and an output signal 80 generated by alternating positive and negative pulses. These are at 81 amplified and fed to the primary winding of a transformer 82, its in the middle tapped secondary winding in a push-pull circuit with the two inputs a flip-flop circuit 83 is connected. The two output signals of the circuit 83 are square-wave turn-on signals 84 and 85 for the first and third phototransistors.

The signal 85 is also used after integration in the circuit 86 to trigger a flip-flop 87, the square and opposite the signals 84 and 85, turn-on signals 88 and 89, each phase shifted by 900, for the two other phototransistors emits. This arrangement is relatively trouble-free and allowed moreover, complicated operations, e.g. B. on the machine tool, with the help of suitable, program signals recorded on the same tape.

Claims (10)

Claims: 1. Arrangement for generating a position of a movable Body relative to a fixed reference system indicating and / or controlling signal by means of an intensity field in which the intensity is spatially based on a periodic Pattern varies, the position of which depends on the body position relative to the reference system, and by means of a measuring sensor device assigned to the intensity field and resting in the reference system with at least two sensors emitting electrical signals, the intensity values determine at those points of the spatial pattern at which the phases of the pattern are different from each other, characterized by the union of the following Features: a) a cyclically operating switching device (33, 34, 35) that controls the individual Switches on the sensor (16) in different areas of the switching cycle; legs summing device (19) following the switching device, in which a row (38) of the successive output signals (37) of the individual sensors will; c) a phase comparison device (49), which one of the relative phase position each one output signal (21) of the summation input direction to reference signal (22) of the respective switching cycle corresponding signal (23) is generated. 2. Arrangement according to claim 1, characterized in that the arrangement the sensor (16) is chosen so that the phase of the intensity pattern (20) at the measuring point of each individual sensor from that at the measuring point of the first Sensor differs by l + A, n + B etc. periods of the pattern (n = Total number of sensors; A, B etc. = any whole numbers). 3. Arrangement according to claim 1 or 2, characterized in that for generating an illumination field with a spatial, periodic intensity pattern (20) a diffraction grating (12 or 13) is provided and that a diffraction grating is one of the number of sensors (16) has a corresponding number of subdivisions. 4. Arrangement according to claim 1 to 3, characterized in that for Activation of the measuring sensors (16) are used to store square-wave signals on tape. 5. Arrangement according to claim 1 to 3, that for switching on the sensor (16) a square wave generator (31) is used, the output signal of which in a delay circuit (34) in mutually phase-shifted control signals for the individual sensors associated electronic switch (35) is reshaped. 6. Arrangement according to claim, characterized in that the signal of the square wave generator (31) the reference signal used for phase comparison (22) is derived. 7. Arrangement according to claim 6, characterized in that; that between Square wave generator (31) and delay circuit (34) Frequency divider (33) are switched on. 8. Arrangement according to claim 4 to 7, characterized in that four Sensors (16) are provided. 9. Arrangement according to claim 1 to 8, characterized in that the Switching device (33, 34, 35) instead of the measuring sensor (16) at least two das Turns on light sources generating the intensity field. 10. Arrangement according to claim 1 to 9, characterized in that the output signal (23) of the phase comparison device (49) in a reset circuit for changing the position of the body arranged servo device (24) supplied will. Considered publications: German Patent Specifications No. 849 454, 899 534, 925 454, 1040 748, 1040 268, 1 609; Electrical engineering (1957), no. 35, pp. 284 to 286.