FR2527802A1 - INCREMENTIAL-TO-DIGITAL CONVERTER - Google Patents

Abstract

AN INCREMENTIAL-DIGITAL CONVERTER FOR CONVERTING A, B POSITION SIGNALS FROM A PULSE GENERATOR 3 REPRESENTING THE POSITION AND DIRECTION OF A MOBILE OBJECT 11, INTO A TOTAL PROVIDED BY A REVERSIBLE POSITION COUNTER 6, INCLUDES A DIRECTION DISCRIMINATOR 21 PRODUCING FROM THE A, B POSITION SIGNALS A DIRECTION SIGNAL R DETERMINING THE COUNTER DIRECTION OF THE COUNTER 6 AND A FRONTS DETECTOR 22 PRODUCING RHYTHM PULSES COUNTED BY THE COUNTER 6. THE DIRECTION DISCRIMINATOR INCLUDES TWO LOCKERS D 23, 24 TO WHICH ARE APPLIED LEDIT POSITION B DELAYED SIGNAL AND THE OTHER A NON DELAYED SIGNAL ON INPUT D AND THE DELAYED RHYTHM SIGNAL OF THE FRONTS DETECTOR 22. AN ADDITIONER CIRCUIT 27 PRODUCED FROM THE SIGNALS OF EXIT OF TILES 23, 24 THE DIRECTION SIGNAL. A FREQUENCY DIVIDER BY FOUR 5 IS INTERCALED BETWEEN THE FRONT DETECTOR 22 AND THE POSITION COUNTER.

Description

The present invention relates to an incremental-digital converter.

  incremental-to-digital converter for converting two phase shifted position signals from a pulse generator and representing the position and direction of an object moving in two opposite directions, into a magnitude

  digitally representing the position, using a comp-

  reversible position sensor and signal generator

  deriving from position signals a signal of

  section determining the counting direction of the po-

  isition and rhythm pulses intended to be comp-

  ted by the position counter and comprising an edge detector deriving from each edge of the position signal a rhythm pulse and a direction discriminator capable of receiving, on the one hand, the rhythm pulses of the edge detector and other hand the signals

  position to produce the direction signal and behave

  both a flip-flop capable of receiving the position signal.

  The pulse generator generally has a very high resolving power so that even when the moving object is moved very little, a large number of position pulses are produced Due to this high resolving power, position pulses can also be produced when the moving object is moving in the opposite direction to the desired direction, for example in the event of tremors or vibrations when the moving object

  is at rest In the case of a converter known to this.

  type, these parasitic pulses (corresponding pulses

  to a parasitic displacement) are added in a comp-

  reversible sensor specially designed for parasitic pulses, when establishing a directional movement

  opposite to the set direction, by interruption of production

  count pulses counted by the counter

  position and after crossing the para- movements

  sites in the set direction, sending pulses of

  counting is only released when the number of pulses

  counting sions exceeds the sum of the counting pulses

  tage produced in the opposite direction Therefore, the total of the position counter does not always correspond exactly to the position of the moved object, which is the case anyway when the moving object moves in the wrong direction, but also when it returns in the right direction as long as it has not passed through the initial return point If the pulse counter

  parasite is still full at the start of a movement of the ob-

  mobile jet, it must first be reset to zero using "right direction pulses" before starting the process of counting the actual position This is disadvantageous in many practical cases, such as in the case of the digital control of a turntable and many machine tools, because the first part of the movement is thus lost. In addition, in the case of known converters, the pulse pulses are not

  obtained only from the edges of said position signal.

  This does not allow reliable phase discrimination to be determined to determine the direction of movement, because the tolerances relating to the pulse rates of the position signals are relatively large and are for example 10%, while on the other hand , the phase shift of the two position signals can deviate from the normal phase shift of 90, by a value of 45, i.e. 50% These errors directly affect the evaluation of the value

actual position.

  The object of the invention is to provide a converted

  sor of this type capable of determining the position of the ob-

  3. mobile jet with greater precision, even in the case

  of moving in the wrong direction.

  In accordance with the invention, this object is achieved

  by the fact that said flip-flop is a flip-flop D whose

  input D is connected to the output of a delay circuit which

  directly receives said position signal, that the discrimi-

  direction indicator has a second flip-flop D whose input D directly receives the other position signal

  and an adder circuit connected downstream of the two bas-

  cules D, that the edge detector also produces a rhythm pulse on each edge of the other position signal and that the pulses from the edge detector are sent to the clock inputs of flip-flop D.

  With this device, the total of the po-

  sition corresponds at all times to the real value of the

  position of the moving object The parasitic pulse counter

  tes is eliminated The fact of detecting all the edges of the two position signals has the advantage of allowing as soon as possible the determination of a modification of the direction of movement of the mobile object with a high resolving power. directions of movement are carried out at low cost by using the D scale and the adder circuit The delay circuit

  ensures that the value of the position signal im-

  medially before one edge of said position signal is comparable with the value of the other position signal before the next edge of this other position signal in the addition circuit for effecting direction discrimination Similarly, the value of amplitude before an edge Audit position signal can be compared to the amplitude value immediately after an edge of the other signal

of position.

  It is therefore preferable to place between the output of the edge detector and the clock input of said flip-flop D a delay circuit whose delay time

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  is less than that of the delay circuit connected upstream of input D This ensures that the amplitude of the other position signal has stabilized before detection which

  takes place immediately after the front of this po-

sition =

  The delay circuit can be an internal circuit

  grateur RC Its installation is particularly simple because it

  requires only a resistor and a capacitor.

  Between the edge detector output and the

  clock of the position counter, is preferably

  a frequency divider dividing the frequency by four

  pulse frequency This frequency divider eliminates

  frequency fluctuations due to permissible variations

  hl "form factors of the two position signals, affecting the rhythm pulses produced from all the edges of the position signals, since it transmits to the position counter only one rhythm pulse out of four, and that the defined time intervals

  all the four impulses of the rhythm are constant when

  that the speed of movement of the moving object is cons-

  aunt, despite the fact that the form factors of the two

  nosition signals are different.

  The frequency divider may also include a reversible pulse counter whose direction input

  counter is connected to the output of the di-

  rection The counting direction of this pulse counter is thus reversed as soon as the direction of movement of the moving object is reversed, so as to avoid errors of

  counting when the direction of movement is reversed.

  The invention and its applications are described below.

  with reference to the drawings which represent an example

  ple of preferred realization and in which:

  FIG. 1 represents a block diagram of a circuit

  position control cooked with a convertor

the invention; and

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  Figures 2 to 4 show the diagrams

  signal times used in the servo circuit

position of Figure 1.

  The position control circuit represented

  shown in FIG. 1 comprises a regulator 1, a servomotor 2, a pulse generator 3, a signal generator 4, a frequency divider 5, a position counter 6 and a

nominal value generator 7.

  A predetermined numerical nominal value in

  the nominal value generator 7 is compared in the re-

  controller 1 to a predefined actual digital position value

  completed in position counter 6 The difference ob-

  * held during the comparison, i.e. the difference in

  glage, is transformed into an analog positioning signal

  logic and sent by a conductor 8 to the servomotor 2.

  This positions according to this position signal.

  ment, if necessary by means of a bevel gear mechanism 9 and a threaded rod 10, a movable object 11 such as the plate of a machine tool, in one or other of the

  two directions indicated by the double arrow 12.

  The adjustment of the angle of rotation, the number of turns and the direction of rotation of the shaft 13 of the servomotor

  2 and therefore the position and direction of movement

  cement of the moving object 11, are transformed into two si-

  position A and B signals out of phase with each other

  be about 90, having a rectangular shape and a fac-

  shape tester (ratio of the duration of the pulse to the

  riode) by about 50%, by means of the pulse generator 3 also coupled to the shaft 13, on two output terminals 14 and 15 The fact that the position signal A is in advance or in phase lag with respect to the other position signal B means that the servomotor 2, or that the object

  mobile 11, is actuated in either direction.

  On the other hand, the number of pulses of the two po signals

  sition A and B from the start of the movement is a measure of the Darcouru path or the position of the moving object It

  from the starting point of the movement.

  For this purpose, the pulse generator 3 includes

  carries a screened scale 16 driven by the servomotor 2, the frame of which is detected by sensors spaced from one another by an interval corresponding to the phase shift of 900 desired between the position signals, and formatting the position signals rectangular A and B by means of

  pulse shaping circuits 17 and 18.

  The position signals A and B are sent to the signal generator 4 This produces on an output conductor 19 a direction signal R from the sign of the relative phase shift of the position signals A and B, and on a second conductor output 20, a rhythm pulse T from each edge of the two position signals A and B. For this purpose, the signal generator 4 includes a direction discriminator 21 and an edge detector

  22 The direction discriminator 21 contains two switches

  D 23 and 24, a delay circuit 25 connected to the input D of the flip-flop 24, a second delay circuit 26 connected to the clock input C of the two flip-flops 23 and 24 and an adder circuit 27 in the form of an OU-EXCLUSIVE gate connected to the outputs Q ("true" outputs) of the two flip-flops 23 and 24 The delay time t 1 of the delay circuit 25 is significantly shorter than half of the smallest period of one position signals A and B and the delay time t 2 is less than t 1 The delay circuits 25 and 26 delay the front and rear edges of their signals

  input of the same delay time t 1 or t 2.

  The edge detector 22 comprises at the input an OU-EXCLUSIVE door 28 connected to the conductors 14 and 15, a

  delay circuit 30 connected to the output of the gate OU-EXCLU-

  SIF 28 by a conductor 29 producing the same delay time t 1 as the delay circuit 25 and another gate

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  OR-EXCLUSIVE 31, one of the inputs of which is connected to the output of the delay circuit 30 by a conductor 32 and the other of which

  input is connected directly to the door output OU-

  EXCLUSIVE 28 By a conductor 33 and the conductor 29 The rhythm pulses T produced at the output of the edge detector 22, that is to say from the OR-EXCLUSIVE gate 31 are firstly sent to the input of the circuit delay 26 by a conductor 34 and on the other hand, in the form of inverted clock pulses T at the moven of a NON 35 element, at the

output terminal 20.

  The frequency divider 5 includes a counter

  of reversible pulses 36 which divides by four the frequency

  quence of rhythm pulses T applied to its input

  clock C Dar conductor 20, i.e. a pulse

  output rhythm T 4 is produced every four pulses of rhythm T on the output conductor 37 which

  is connected to the clock input C of the position counter 6.

  The frequency divider 5 further comprises a NAND gate 38 combining the output signals Q 1 and Q 3 of the pulse counter 36 and connected via a delay circuit 39 to the input of a NAND gate 40 playing

the role of seesaw.

  The output signal C O is also applied to the other input of the NAND gate 40 via 2-5 of another delay circuit 4-1 The delay times T 3 of

  delay circuits 39 and 41 are less than t 1, but may

  however, may be chosen equal to this value.

  The output of the NAND gate 40 is connected by the conductor 37 to a control input P of the counter

  of pulses 36 which, when it receives a signal "1" pro-

  here is the oreregulation of the counter 36 to a number applied in the form of binary signals to the inputs Pl to P 4 This number is the binary number "0001", that is to say the decimal number "1", or the binary number "0100", that is to say the

  decimal number "4", depending on whether the direction signal R ap-

  plied directly at input P 1, or at input P 3 after inversion by a NON 32 gate, is a signal "1" or a

"O" signal.

  The direction signal R is also sent to the control inputs of the counting direction U / D of the counters 6 and 36 so that the counters count "forward" in the case of a signal R to state 1 and "backward" in the case of a signal R in state O. The operating mode of the servo circuit shown in FIG. 1 and more is described below.

  specifically, from the incremental to digital converter

  by the signal generator 4, the frequency divider

  quence 5 and the position counter 6 while referring to

fence in figures 2 to 4.

  From position signals A and B in Figure 2, whose relative phase shift allows the counter to

  position 6 to count down (R = "O"), the door OU-

  EXCLUSIVE 28 produces the signal S (Figures 1 and 2) whose frequency is twice that of one of the position signals A and B and which also has a form factor of 0.5 It apuara Lt therefore at the output of the delay circuit 30 a signal SI delayed by time t 1 relative to the

  signal S (Figures 1 and 2) This signal S 'is again

  put in the logic circuit 31 to an OU-EXCLUSIVE combination with the non-delayed signal S, so that it appears on the conductor 34 of the pulses of rhythm T (FIGS. 1 and 2) whose frequency is however four times higher

  than that of position signals A and B The front edges

  laughing pulses of rhythm T agree with all

  edges of nosition signals A and B The duration of the pulses

  sions of rhythm T corresponds to the delay t 1 of the delay circuit 30 The pulses of rhythm T are inverted by the gate NO 35, since the advancement of the counter 36 is triggered by the front edges (the transitions

  0-1) rhythm pulses T applied to the clock input

  accommodates C, but must be slightly delayed with respect to the edges of signals A and B so that after a variation in amplitude of the direction signal R synchronized with the front edge of the rhythm signal T, this it has stabilized before the counting process begins.

  The rhythm pulses T are also applied.

  quées at the clock inputs C of flip-flops 23 and 24 taking into account that rhythm pulses T 'delayed by a time t 2 Then

  that the position signal A is applied directly to the

  input D of flip-flop 23, the position signal B is applied

  qué at the entry D of rocker 24 in the form of a signal of

  position B 'delayed by a time t 1 by the delay circuit.

  The storage in flip-flops 23 and 24 of information

  mations present at the inputs D is carried out each time with the front edge (transition 0-1) of a rhythm pulse T 'applied to the clock input C, that is to say if a signal " 1 "appears at the input D of one of the flip-flops 23 and 24 and that a rhythm pulse is produced at the clock input C, the flip-flop D concerned acts in such a way that a signal" 1 " is also produced at its Q output If it already supplied a signal "1" at the Q output, this

  signal "1" remains present Each modification of the information

  tions (transition 1-0 or 0-1) at input D is first stored in memory by the following rhythm pulse T 'The adder circuit 27 then always produces a signal

  R = "1" ("forward counting") if the

  signals present on the Q outputs of flip-flops 23 and 24 are different and if not, it produces a signal

  direction R = "O" ("countdown") If by the following

  te, the position signal B immediately before an edge of the position signal B coincides with the position signal A before the next edge of the position signal A, or if the position signal B after an edge of the position signal B coincides with position signal A immediately after

  the next edge of the position signal A, -the circuit addi-

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  actuator 27 produces a "" signal ("countdown countdown").

  As the rhythm pulses are produced from the fronts of the position signals, but that a pulse of

  rhythm must also allow acquisition (setting

  moire) of the position signal value immediately

  before the front of the position signal triggering the im-

  rhythm pulse, the position signal B is delayed by a time t, by the delay circuit 25 so that the rhythm pulses T produced from the edges of the position signal B always appear a time t 1 before the corresponding edges of the delayed position signal B '(actually detected) (compare B' and T in Figure 2) Furthermore, the rhythm pulses must however also allow the acquisition of a value of the position signal A immediately after a signal front

  of position A which triggers them Consequently, the pulses

  rhythm tions T 'effectively detecting the position signals A and B are further delayed by time t 2 with respect to the rhythm pulses T produced directly from the edges of the position signals, to ensure that the position signal A stabilized at the news

  value after the edge that triggered the impulse considered

  Before the appearance of the rhythm pulse T 'As the rhythm pulses T' must also occur

  before the edges of the position signal B which triggers them

  chent, t 2 is chosen lower than tl Instead of the OU-EXCLUSIVE gate 27 realizing the antivalence (non-equivalence) of the position signals A and B according to the logic function (A & B) v (A & E) (the symbol "&" representing an AND gate

  and "v" an OR gate), a circuit can also be provided

  cooked logic achieving equivalence according to the lo-

  logic (A & B) v (A & B) as an adder circuit 27, if the counters 6 and 36 which both receive the

  direction signal R should not count "backward".

  in the case of the relative phase shifts of the position signals it

  A and B shown in Figure 2, but "forward".

  The role of the di-

  frequency finder 5 with reference to Figure 4 In pra-

  tick, the form factors of position signals A and B can differ by 50%, for example due to the adjustment errors of the pulse generator 3 Unbalanced position signals A and B of this type are represented in FIG. 4, their asymmetry being however exaggerated

  for clarity therefore, the rhythm impulses

  me derived from the fronts of these position signals

  A and B (Figure 4) are also separated by intervals

  the different Despite the regular rotation of the shaft 13, or the regular movement of the object 11, the acquisition of the real value would therefore be done irregularly in

  the position counter 6, so that the process of re-

  setting would be unstable or the nominal value could not be reached precisely Due to the division of the rhythm pulses by four, we get

  a more regular pulse interval for im-

  rhythm pulses T 4 at the output of the frequency divider 5,

  -so, although in practice the form factors of si-

  position signals A and B can be different, their frequency or period is constant when the speed of the moving object is constant In addition, the position counter 6 has a lesser counting capacity than that of a position counter advancing one step at a time

  pulse or both pulses (for the same path

  maximum jet from the moving object).

  So that the binary counter 36 of the frequency divider 5 produces a CO output pulse (FIG. 2)

  every four pulses of rhythm T, or that the divi-

  frequency generator 5 produces an output rhythm pulse T 4 every four rhythm pulses T, the counter 36 is brought back by each output rhythm pulse T 4 to a starting value determined by the direction signal R on the inputs of preset P1 to P4, that is to say either to "0001" = 1, or to "O 100" = 4 In the case of counting towards the front, the total of counter 36 describes cyclically in decimal representation the sequence of numbers 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, etc. When changing from "4" to "1", the counter 36 temporarily displays the value "5" = "0101", the output signals Q 1 and Q 3 (Figure 3) both being at "1" This is achieved by the NAND gate 38 which gives a signal "O" 538 which after being delayed by a time t 3 oar the delay circuit 39 and reversed by the door

  NAND, is applied to the reset input P of the comp-

  36 as a reset pulse (or at the exit

  tle of frequency divider 5 as a rhythm pulse

  output) T 4 The counter 36 is thus reset to "1" (= "0001"), so that the counting process can resume at 1, 2, 3 In case of counting down (R = "1 "), the total of the counter 36 describes in reverse the sequence of numbers mentioned more halit, that is to say in the following order: 4, 3, 2, 1, 4, 3, 2, etc. When d 'a change from "1" to "4", the counter 36 produces a pulse "O" Co (FIG. 2) which

  is delayed by time t 3 by delay circuit 41 and in-

  poured through the NAND gate 40 so that the reset or rhythm pulse T 4 appears at the output of

  NAND gate 40 which triggers the reset to zero of the

  tor 36 and therefore determines the end of the pulse

  "O" Co The duration of the output rhythm pulses corresponds to

  therefore also lies at the delay time t 3.

  The nosition counter 6 counts "forward" the rhythm pulses it receives during the duration of the

  signal "1" R, and counts "countdown" the rhythm impulses

  me T 4 that it receives for the duration of the countdown signal R = 0, so that the total of the position counter 6 always corresponds to the real value of the position of the moving object 11 This real position is compared in the regulator 1 with the nominal value introduced in the nominal value generator 7, to readjust the position of the moving object 11 in case it

an adjustment deviation occurs.

Claims (4)

  1 Incremental-to-digital converter for converting two phase-shifted position signals from   a pulse generator (3) which represents the posi-   tion and direction of a moving object in two opposite directions (11), in a magnitude representing numerically   position using a reversing position counter (6)   signal and a signal generator (4) deriving from the position signals (A, B) a direction signal (R) determining the direction of counting of the position counter (6) and of the rhythm pulses intended to be counted by the position counter, and comprising an edge detector (22) drifting from each edge of said signal   position a pulse of rhythm (T) and a discrimina-   direction printer (21) capable of receiving on the one hand the im-   rhythm pulses (T) of the edge detector (22> and of   apart from the position signals (A, B) to produce the direction signal (R) and which includes a rocker (24)   to which said position signal (B) is applied, ie   characterized in that said scale is a D scale (24)   whose input D is connected to the output of a circuit   late (25) at which said position signal (B) is direct-   sent, in that the direction discriminator (21) comprises a second flip-flop D (23) whose input D directly receives the other position signal (A) and an adder circuit (27) connected to the outputs of the two flip-flops D (23, 24), in that the edge detector (22) also produces a rhythm pulse (T) on each edge of the other position signal (A) and in that the edges detector pulses are sent to clock inputs (C) D flip-flops (23, 24).   2 Converter according to claim 1, ca-   characterized in that a delay circuit (26) is inserted   between the edge detector output and the clock input   lodge (C) of said flip-flop D (24), its delay time (t 2) being less than the delay time (t 1) of the delay circuit (25) connected to the input D.   3 converter according to claims 1 and 2,   characterized in that the delay circuits (25, 26) are RC integrator circuits.   4 Converter according to claims 1 to 3,   characterized in that a frequency divider (5) dividing the frequency of the pulses by four is interposed between the output of the edge detector (22) and the clock input (C) of the position counter (6).   Converter according to claim 4, characterized in that the frequency divider (5) comprises a reversible pulse counter (36) whose input of   counting direction (U / D) is connected to the discrimi- direction nator (21).