FR2635488A1 - ADVANCE SYSTEM FOR TRACANTE TABLE EXECUTING LARGE DRAWINGS ON CONTINUOUS PAPER - Google Patents

Abstract

This plotting table comprises means forming a support surface intended to support, in order to carry out a plotting, a portion of a long sheet of continuous paper and means for carrying a supply reel and a take-up reel allowing, respectively, to deliver and receiving an elongated continuous sheet of paper, the paper passing over the support surface from the take-up reel to the take-up reel. According to the invention, it is characterized by drive means 46 making it possible to drive the receiving reel in rotation in the winding direction so as to draw the paper from the supply reel and make it advance on the support surface, as well as means 64, 90, 120 for feeding these drive means 46 so as to advance the paper of the sheet continuously on the support surface at a predetermined speed independent of the diameter of the take-up reel.

Description

The present invention relates to plotters in which one

  draws graphic elements on a material in the form of a long continuous sheet of paper, and in which the sheet material is advanced over a support surface, effective execution of the drawing taking place on the part of the material carried by the support surface, and the finished pattern having a significantly greater length than the length of the support surface in the advancing direction of the sheet material; the present invention more specifically relates to means for controlling the advance of the sheet material in

such a plotter.

  The plotters of the type to which the invention belongs are generally used with paper as a sheet material, paper on which a writing instrument belonging to the plotter, such as a pen or a pencil, executes the drawings. given this, we

  use for convenience, in the description below, the

  term "paper" to refer to the sheet material. However, materials other than ordinary paper, for example continuous plastic film or continuous photographic film, can sometimes be used as a sheet material. The term "paper" used here should thus be interpreted broadly, including all types of sheet materials that may be

  used with the plotter in question.

  In the plotters where a long sheet of paper is fed continuously over a support surface, it is important to accurately measure the advance of the paper so that a fraction of the pattern formed on a certain portion paper corresponds exactly to another fraction of the pattern formed on an adjacent portion of the paper. For example, the plotter can be operated portion by portion, in which case the paper is held fixed relative to the support surface while a portion of a pattern is drawn on the paper covering the support surface by means of a writing instrument moved on the abscissa and ordinate by the plotter. When this part of the drawing is completed, the drawing process is suspended and the paper is continuously fed over the support surface to bring a new portion of paper. We then resume tracing on the new portion to form another part of the set to draw, and we repeat this alternation of tracing and paper advances until completion of the drawing. This requires that the paper be precisely located at the end of each step in advance, to allow proper alignment of the adjacent parts of the drawing. It is also important for the efficiency and timeliness that paper advance movements are

  carried out as quickly as possible.

  In the plotters of the aforementioned type, it is also generally necessary, before starting a drawing, to initialize to a certain state the means used to detect the movement of the paper in the direction of advance so that they can indicate correctly, relative to a fixed reference point relative to the support surface, the position of a given reference point of the paper, and this initialization process often involves

  wasting a significant amount of paper.

  The main object of the invention is thus to propose a system for controlling the advance of the paper for a plotter in which a paper is continuously moved over a support surface, this control realizing a precise positioning of the paper relative to the surface

  support. In this spirit, the invention has more particularly

  The object of this invention is to provide such advance control of the paper, which is more specifically suitable for operation of the plotter portion by portion, and capable of ensuring precise positioning of the paper with respect to the surface.

  support at the end of each paper advance.

  The object of the invention is also to provide paper advance control of the aforementioned type, in which the movements of paper advance take place in a relatively short time, in order to maximize the operating speed of the plotter. With this in mind, the paper feed means comprise a paper-supplying spool and a paper-receiving spool, the receiving spool being driven by a motor in order to carry out the advance movement of the paper, and the motor being actuated with such so that the paper has, regardless of the diameter of the receiver coil, a uniform speed. predetermined above the support surface during most of

every move in advance.

  Another object of the invention is to propose a paper advance control system of the aforementioned type, comprising a paper advance sensor which can be initialized in a certain state with respect to the paper without risk of waste.

noticeable paper.

  Other objects and advantages of the invention will appear at

  reading the detailed description below of a mode

of realization.

  For this purpose, the present invention provides a plotter comprising a support surface carrying a portion of a long sheet of paper continuously, the support surface being fed with paper continuously by supply and receiving coils. A suitable drive drives the take-up spool to pull the paper out of the supply spool and advance it over the support surface, and this drive is activated by a driver stage associated therewith, so that the feed is advanced. paper on the support surface at a predetermined speed

  independent of the diameter of the receiver coil.

  The invention also resides in the means for feeding the drive of the receiver coil, which comprise a measuring wheel coming into contact with the paper, rotated by the latter during an advance movement and having zones alternately opaque and transparent cooperating with a light source and a photodetector so as to produce a series of electrical pulses whose intervals between the rising edges correspond to a fixed, fixed angular rotation of the wheel and therefore to a fixed displacement, paper. These pulses are converted into a paper speed signal which is compared to a reference speed signal to produce an error signal that feedbacks the feed of the drive motor to maintain the speed of the drive. advance of the paper to the predetermined value set by the reference speed signal. The pulses are also measured and used to determine the length of the paper feed movement since the beginning of a feed movement, this length measurement being itself used to control the power supply stoppage of the motor. 'training

at the end of a move in advance.

  The invention also resides in the control means for advancing the paper at a predetermined speed by using a DC drive motor which, when fed continuously with a voltage, moves the paper to a speed greater than the predetermined speed even if the diameter of the takeup spool is minimal, the speed of the motor then being controlled, so that the paper moves at the predetermined speed, by applying a tension to the motor with

  hashing or pulse width modulation.

  The invention also resides in the fact that the drive motor is controlled by a control stage operating in response to signals from two output lines of a processor and allowing either to supply the motor with modulation of the width of the motor. The impulse is to short-circuit the terminals of the drive motor in order to obtain a dynamic brake effect from the motor. The signals appearing on the two input lines of the control stage and the operation of the control stage are such that, if one or the other of the two lines comes to

  find in the air, the engine will be disabled.

  We will now describe an exemplary embodiment of

  the invention, with reference to the accompanying drawings.

  FIG. 1 is a plan view of a plotter including a paper advance control using

the present invention.

  FIG. 2 is a perspective view in partial section, more or less schematic, showing in greater detail a part of the paper advance control system, the sectional part of this figure being taken along line 2-2 of FIG.

Figure 1.

  Figure 3 is a schematic diagram of the system of

  control of the plotter of Figure 1.

  FIG. 4 is a schematic diagram showing in more detail the control stage of the paper advance motor.

Figure 3.

  Figure 5 is an elevational view of the measuring wheel

of Figure 2.

  Figure 6 is a schematic diagram illustrating the power supply of the drive motor at two different speeds. Fig. 7 is a truth table showing the engine states which are terminated by the different combinations of input signals applied to the engine control stage. FIG. 8 is a schematic diagram showing functionally how the control processor converts the pulses delivered by the measurement wheel to control the signals applied to the stage of

  piloting the paper feed motor.

  FIGS. 1 and 2 show, by way of example, an X-Y 12 plotter comprising a control system of

  the advance of the paper embodying the present invention.

  This plotter is of the same type as that described and illustrated in a US patent application filed May 17, 1988 under number 195 128, in the name of the Applicant (inventor Heinz Joseph Gerber), entitled Progressive Plotter with Unidirectional Paper Movement, to which one

  will be able to refer for more details.

  For the purposes of this application, it is sufficient to note that the plotter 12 has an upwardly facing support surface 14 formed by a plate 16 extending between two end pieces 18 and 20. The support surface 14 is Rectangular general shape, and has two elongated lateral edges 22 and 24. A paper-supplying reel 26 is, in the vicinity of the right lateral edge, 2, rotated on an axis 28 parallel to the lateral edge 22 and located lower than that- this. A receiver coil 30 is, in the vicinity of the left lateral edge 24, rotated on an axis 32 parallel to the edge 24 and

located lower than this one.

  Tracing is performed on the portion of the paper 34 located on the support surface 14 by means of a pen 36 or other writing instrument carried by a support carriage 38 that can move in the direction of coordinates shown X along the length of the paper. a main carriage 40 of elongate shape or carriage Y. The main carriage 40 is carried at each of its ends, with the possibility of displacement in the direction of coordinates illustrated Y, by two guide rails 42, 42 fixed relative to the support surface. 14 and carried at their ends by the

end pieces 18 and 20.

  Paper 34, in the direction of arrow 44 of FIG. 1, is advanced by means of a paper drive motor 46 which drives the take-up spool 30 counterclockwise, as illustrated. Figure 2, in order to achieve this advance movement of the. paper on the support surface. The displacement of the pen 36 in the X and Y coordinate directions is obtained for the pen carriage 38 and for the main carriage 40 by a cable drive system, the drive of the pen carriage 38 comprising a drum cable 48 driven by a motor X 50 acting on a cable 52, and the drive of the main carriage 40 comprising a cable drum 54 driven by a motor Y 56 acting on two cables 58, 58 respectively associated with each of the opposite ends of the carriage 40. When feeding the paper drive motor 46 in order to advance the paper 34, it is preferable to apply the paper

  the supply coil 26 a force causing a delay effect.

  This delay effect force can be obtained in various ways but, in the case illustrated, it is obtained by means of a fixed friction disk 60 against which is applied the adjacent end of the coil 26 by means of a flange biased by spring 62 coming into contact with the opposite end of the supply reel and coming to urge it under the pressure of the spring,

against the friction disc 60.

  The plotter 12 is of the type with progressive tracing, with unidirectional advance movement of the paper on the

  support surface in the direction of the arrow 44.

  That is, with the conventions of Figures 1 and 2, the paper 34 moves only from right to left with the pen 36 being moved to execute the drawing on the paper 34 carried by the surface support, this pen being moved relative to the support surface along the two directions of X and Y coordinates. Generally, the drawing. that is executed is much longer than the interval separating the lateral edges 22 and 24 of the support surface, and is carried out progressively starting at its left end and executing it gradually by gradually moving the process of tracing from the left end of the drawing to the right end of the drawing, while advancing the paper 34 from right to left above the support surface 14 to compensate for the advance movement of the tracing process . Different modes of cooperation between the tracing process and the advance movement of the paper can be used, but most often the drawing is formed portion by portion, alternating tracing steps and paper advance steps. In other words, when a drawing portion by portion is executed, after a portion of paper 34 has been moved on the support surface 14, it is held fixed relative to the support surface while performs on this surface a part of the overall layout. The tracing procedure is then interrupted and the paper is advanced to bring a new portion of paper onto the support surface. The tracing procedure is then resumed in order to execute another part of the tracing on the portion now on the support surface, and these alternations between tracing and advance movements of the paper are continued until the entire route has been completed. In order for the part of the drawing executed on a portion of the paper to be connected to the part executed on the adjacent portion, it is necessary that the amount of paper that is advanced during each advance movement is determined accurately. In addition, in order to maximize the speed of operation of the plotter, it is essential that the advance movements of the paper are also

as fast as possible.

  According to the invention, there is provided in the plotter 12 a paper feed control system for obtaining, as desired, a paper feed movement that is both accurate and fast. An essential part of this system lies in a paper feed sensor operating in response to the movement of the paper with respect to the support surface and producing, as the paper advances, a train of electrical pulses whose pulse interval corresponds to moving the paper. Thus, for example, the interval between the rising edges of two successive pulses represents a given displacement of the paper relative to the support surface. Without departing from the scope of the invention, it is possible to use various means to obtain electrical pulses representative of the paper advance movement, but preferably this indication of the advance movement is obtained by a sensor block 64 carried by the right guide rail 42 and having a measuring wheel 66. As can be seen more clearly in FIG. 2, the wheel 66 is carried by an arm 68 in rotation around an axis 70 perpendicular to the direction of travel 44 of the paper. The arm 68 is pivotally connected to the guide rail 42 with the possibility of displacement about an axis 72 parallel to the axis 70 of rotation of the wheel. The arm 68 is urged by gravity, as well as optionally by an additional spring if necessary, in the clockwise direction about the axis 72, which has the effect of applying the periphery of the wheel 66 in contact with the paper 34, and rotate the wheel clockwise, i.e. in the direction of the arrow 74, when the paper

  moves in the direction of arrow 44.

  The wheel 66, as best seen in FIG. 5, is made of glass or other optical material and has six opaque sectors 88, each sector 76 and 78 having an angle at the center of 30. On either side of the measuring wheel 66, as can be seen in FIG. 2, there is a light source 80 and a photodetector 82, the source 80 being placed so as to direct a light beam 84 which

  crosses the wheel 66 and hits the photodetector 82.

  When the beam 84 meets one of the transparent sectors 76 of the wheel, it passes through the wheel and hits the photodetector 84, which gives a certain level of electrical output of the detector. When the beam meets one of the opaque sectors 78 of the wheel, it no longer hits the photodetector 82, which produces another level of electrical output of the detector. Thus, as can be seen, when the wheel rotates during a paper advance movement, the photodetector 82 produces a pulse train whose spacing between successive pulses is a function of the movement of the paper. Thus, for example, between the appearance of the rising edge of a pulse and the appearance of the rising edge of the next pulse, it will be known that a given length of paper has been advanced over the support surface. , the exact value of this displacement being a function of the diameter of the measuring wheel 66 and the number of opaque and transparent sectors

constituting the wheel.

  Figure 3 shows the relationship between the paper feed motor 46 and the paper displacement sensor block 64 relative to the remainder of the plotter control system. As illustrated in this figure, the plotter is mainly under the control of a control processor 90. The data determining the plot to be executed by the plotter are delivered to the control processor by an input line 92 from an associated computer-aided design system or the like. The processor is powered by a digital power supply 94 in 5 V continuous. The input data applied to the control processor 90 for the local control of the plotter comes from a keyboard 96. The information useful to the operator, either from the keyboard 96 or from the processor 90, is displayed by a display device.

  liquid crystal 98 by a display logic circuit 100.

  The control processor applies signals to the servo amplifiers 102 which power the X and Y motors 50 and 56 for driving the pen 36 in the X and Y coordinate directions. Encoders 51 and 57, integral in their movement of the X and Y motors, respectively, deliver actual X and Y pen position signals that are returned to the control processor 90 on a position feedback line 104. The processor also outputs signals on a line 106 toward a pen control solenoid 108 located on the pen carriage 38 and for moving the pen to the other writing instrument between a writing position, lowered, and a non-writing position, raised. The DC voltages at the different levels required for the control processor 90 are provided by the circuit of an analog power supply 110. The power supply 110 has as inputs a number of lines 112 from a connected transformer 114, via a switch / filter / fuse block 116, to a suitable source of AC voltage. Lines 112 deliver analog voltages 110 of alternating voltages of different amplitudes, the analog supply comprising rectifiers and filters making it possible to convert these AC voltages into filtered continuous voltages necessary for the control processor. The DC output voltages produced by the analog supply are delivered to the control processor 90 by the line

118.

  A driver stage of the paper feed motor 120, which is preferably located on the same circuit board as the analog power supply 110, is controlled by signals applied to it by the control processor 90 on the line 122. As indicated by line 124 of FIG. 3, the motor control stage 120 controls the activation of the paper advance motor 46. When, as explained above, the motor 46 is energized to allow the advance of the paper, the paper advance sensor 64 is activated and produces pulses representative of the paper feed movement transmitted to the control processor 90 by

  through the feedback line 104.

  FIG. 4 shows in more detail the structure of the engine control stage 120. As illustrated in this figure, the line 122 of FIG. 3 consists in fact of two separate conductors 126 and 128 connecting the processor 90 to the stage 120 internally, the processor 90 operates, as indicated 130 in Figure 4, so as to switch the conductor 126 from a state to ground to an air state. The open state of line 126 corresponds to a BRAKING signal, while the ground state of the line corresponds to a BRAKING signal. As for the conductor 128, the processor operates, internally, as indicated at 132, that is to say by switching the conductor between a state to ground and a state in the air, the state to the corresponding ground at a signal MOTOR and the state in the air

corresponding to a MOTOR signal.

  In response to the signals appearing on the input leads 126 and 128, the motor driver stage 120 operates to either apply a DC supply voltage between the input terminals 134, 134 of the motor 46, which causes the motor to rotate, or to short-circuit the terminals 134, 134, which makes it possible to obtain a dynamic braking effect from the motor. When the motor is powered, it is normally supplied with a voltage of the polarity indicated on the motor terminals 134, 134 of Figure 4, which causes a rotation of the motor in the direction of the winding of the paper on the take-up spool , which pulls the paper from the debtor reel and moves it forward

  on the support surface in the direction of arrow 44.

  However, if desired, the polarity of the power supply voltage applied to the motor can be reversed by pressing the paper reversing push-button 136, causing the motor to rotate in the opposite direction, thereby rotating the receiving coil in the opposite direction of the winding, for example to unwind a completed path. In normal operation, i.e., when the paper reversing pushbutton 136 is not actuated, the motor control stage 120 responds to the signals appearing on the input leads 126 and 128 of the the way indicated by the truth table of Figure 7. That is to say that the engine is powered only if

  the MOTOR signal and the BRAKE signal are simultaneously.

  With each of the other three possible signal combinations on the two lines 126 and 128, the motor is not powered and, in addition, each time the BRAKE signal appears on the line 126 the motor terminals are short-circuited. It is thus obvious, from FIG. 7, that the motor 46 will be de-energized for safety if, by accident, one or the other of the two input leads 126

  or 128, or both, was in the air.

  We will now explain the structure and operation of the engine control stage 120 according to

  the truth table of Figure 7 and from Figure 4.

  The short-circuit or absence of short-circuit of the terminals 134 of the motor is controlled by a controlled rectifier 138 which is excited by a control voltage appearing on the line 140. The line 140 is connected to the conductor 126 by an optical isolator 142, and the conductor 126 is connected to a source of +28 V via a resistor 144. When the conductor 126 is grounded by the processor 90 to give a BRAKING signal, a null potential is applied by the optical isolator 142 at the line 140, which keeps the controlled rectifier 138 in the off state, and thus maintains the terminals 134, 134 of the motor 46 in an unsealed state. Conversely, when the processor places the conductor 126 in the air, which corresponds to the BRAKE signal, a voltage of +28 V is applied to the conductor 136 by the resistor 144, and a corresponding voltage is applied by the optical isolator 142 to the line 140, which switches the controlled rectifier 138 to the conductive state, thus shorting the terminals 134, 134 of the motor and causing the motor 46

a dynamic brake effect.

  If it is assumed that the controlled rectifier is blocked, the power supply of the motor 46 is controlled by a transistor 146. That is to say that when the transistor 146 is in the conducting state, the motor is energized, and when the transistor is in the off state the motor is no longer powered. The state of the transistor 146 is itself controlled by two other transistors 148 and 150. The base of the transistor 148 is connected to the input conductor 126 through the input of the optical isolator 142 so that, whenever A positive voltage appears on the conductor 126. The transistor 148 is switched to the conductive state, which grounds the line 152 connected to the base of the transistor 146 and has the effect of keeping the transistor 146 in the off state. . In other words, when the BRAKE signal appears on the line 126, the transistor 146 is kept in the non-conducting state

  and we do not try to power the engine.

  The transistor 150 has its base connected to the input conductor 128 via a Zener diode 154. When the conductor 128 is grounded by the processor 90, the transistor 150 is kept in the off state and the +28 V voltage is applied to line 152 through resistor 156. This switches transistor 146 to its conductive state and allows motor 46 to be powered by the +110 V DC voltage source shown via the resistor 157 and the line filter 159. When the processor 90 holds the input line 128 in the air, which corresponds to the MOTOR signal, the voltage of +28 V is applied to the base of transistor 150 through resistor 162. This turns transistor 150 on and applies the potential of ground to line 152, thereby blocking transistor 146 and

  thus prevents powering the motor 46.

  As will be explained below, in order to control the speed of the advance movement of the paper during an advance movement of the motor 46, instead of continuously feeding the motor, it is supplied with a chopped voltage or impulse with pulse width modulation, which means that, during the forward movement, the processor 90 repeatedly switches the transistor 146 between its off state and its on state, repeatedly flipping between the MOTOR signals and MOTOR on the conductor 128. In addition to the fact that the activation of the motor 46 in this way turns the receiver coil in the direction of the winding, it is also possible to reverse the power supply of the motor by pressing the button. The push-button 136 of FIG. 4 is pressed. If button 136 is pressed, the coil 158 is supplied with a contactor relay which switches the associated contacts and 162 from their positions illustrated in solid lines towards their positions. itis illustrated in broken lines. In this last position of the contacts 160 and 162, the supply voltage at 110 volts is applied to the motor 46 with the opposite polarity to that indicated, and without bringing into play the controlled rectifier 138 used to short-circuit the motor. , or the power control transistor of the motor 146. Thus, when pressing the paper reversing button the motor 46 will be fed continuously with the entire voltage at 110 volts, which will turn the receiver coil in the opposite direction of the winding and without application of any control of

motor speed.

  In normal operation of the engine control stage, that is to say when the paper reversing pushbutton 136 is not pressed, the processor 90, in response to the electrical pulses received from the block, paper displacement sensor 64 and by application of the signals to the input conductor 126 and 128, controls the motor control stage so as to allow both a fixed and high paper feed speed during most of the movement in advance and a precise stop of the paper movement at the end of each advance movement. The manner in which this is achieved can be understood with reference to FIGS. 6 and 8. As shown in FIG. 8, when the motor 46 is fed with the paper displacement sensor unit 64 produced, in response to the movement of the paper, a train of pulses, such as the one referenced 164, which appears on the line 104 and which is such that the interval 1 between the rising edges of the successive pulses represents a given fixed displacement of the paper relative to

at the support surface 14.

  To control the paper feed speed, pulses 164 are converted in a portion 166 of the converter processor to a signal v representative of the actual speed of the paper. This signal is compared, in a portion 168 of the comparator processor, with a high speed reference signal Vref stored in a portion 170 of the high speed reference memory processor, so as to produce an error signal e applied to control logic and a portion 172 of the pulse width modulator processor. A low speed signal V is also applied to the control logic and the pulse width modulator 172 from a low speed memory 174. To control the start and end of the paper feed movement, the pulses 164 are also applied to a portion 176 of the displacement sensor processor 90. The displacement detector 176 is connected to the control logic and the pulse width modulator 172 by a STOP signal control line 178 and a slow signal control line 180. The motion sensor also has another input line 182

  on which the processor can apply a START signal.

  With reference to FIG. 8, the manner in which the processor 90 performs the advance movement of the paper will now be described. After a portion of the trace has been executed on a given portion of the paper, the processor interrupts the tracing procedure and applies a weak signal to the input line 182 of the displacement detector 170. This causes the two STOP signals to disappear. SLOW lines 178 and 180. In response to the disappearance of the STOP signal, the control logic and the pulse width modulator 172 begin to alternately apply MOTOR and MOTOR signals on the line 128, which causes the power supply to motor 46 by the driving stage of the paper advance motor 120 and the beginning of the advance of the paper. As soon as the paper has begun to advance, the sensor 64 generates pulses 164 which are converted by the converter 166 into a real speed signal Va and compared to the signal Vref so as to produce an error signal e which, by feedback, the control logic and the pulse width modulator will respond in such a way as to reduce the error signal by bringing the motor supply to the state corresponding to the paper drive exactly at the

  speed determined by the signal Vref.

  The motor 46 is selected to provide, when fed continuously with the supply voltage, a rotational speed that is more than sufficient to advance the paper at the desired high speed, even when the reel receiver is of minimum diameter. Therefore, to have the desired high feed rate, it is necessary to run the motor at a lower speed, and this is achieved by hashing or pulse width modulation of the voltage applied to the motor. As can be seen in FIG. 6, this is obtained by causing the processor to divide the power supply duration of the motor into a plurality of successive supply cycles C, C. During a part of each cycle C the motor is powered. and for another part the engine is no longer powered. The upper part of FIG. 6 shows the MOTOR and MOTOR signals appearing on the input conductor 128 and corresponding to a relatively high speed motor operation, while the lower part of FIG. 6 shows the corresponding signals allowing to have low speed motor operation. As can be seen, this is due to the fact that the MOTOR signals are modulated in pulse width by the processor 90 in order to arrive at a control of the speed of the motor. It will also be understood that the speed of advance of the paper is a function not only of the speed of the motor but also of the diameter of the take-up spool. The control system of FIG. 8 has the effect of directly measuring the speed of the paper and keeping it at the desired high value independently of the diameter of the take-up spool, the motor 46 being fed so as to rotate it at the desired speed. , regardless of this speed, in order to maintain the predetermined speed of

  paper regardless of the diameter of the take-up reel.

  The displacement sensor 176 counts the pulses 164 produced from the start of the feed movement by the sensor 64 and, in response to this count, terminates the paper feed movement after a given amount of paper has been fed. displaced, and it is preferably terminated this advance movement with slowing of the motor 46 for a short time before the actual stop. Specifically, the displacement sensor 176 counts the pulses 164 to detect the advance of a first given amount of paper since the start of the feed movement. When this has been detected, the detector produces on line 180 a SLOWING signal, which toggles the control of the speeds of the control logic and the pulse width modulator 172 of the error signal delivered by the control circuit. comparison 168 to the low speed signal delivered by the low speed reference 174. The control logic and the pulse width modulator 172 then deliver to the driving stage of the paper feed motor, at each cycle of supply, the MOTOR pulses of reduced duration, which operates the motor 46 at a significantly lower speed than during the previous phase of the advance movement. Then, when the displacement detector 176 detects that, since the beginning of the advance movement, the paper has advanced by another amount, the detector produces on the line 178 a STOP signal, which causes the application of the control and the pulse width modulator 172 of a MOTOR signal, applied continuously, on the conductor 128 and a BRAKE signal on the line 126, which has the effect of interrupting the power supply of the motor 46 and short-circuiting its input terminals to achieve a dynamic braking effect, which immediately immobilizes the motor 46 and stops the movement in advance

corresponding paper.

  The processor 90 then triggers and controls a new tracing procedure on the portion of paper that is now carried by the support surface. At the end of this procedure, the tracing process is stopped and another displacement signal is applied to the displacement detector 176, which makes it possible to start a new advance movement of the paper which takes place in the same manner as explained. higher, and we continue to alternate paper advance movements and -training procedures up

completion of the route in question.

  When a new trace is started, the sensor 64 is initialized by slowly moving the paper forward until the rising edge of a pulse appears.

  164, and we take as reference position the initialisation

  the positioning of the paper and the measuring wheel 166 at this time. We see that we reach these initialized positions with a maximum of 60 of rotation of the measuring wheel, which means that we waste only very little

  paper during this initialization process.

Claims (10)

  A plotter for creating graphic patterns on a long sheet of paper continuously, said plotter comprising: means forming a support surface for supporting, for tracing, a portion of a long sheet of paper continuously, and - means for carrying a supply reel and a take-up reel for respectively delivering and receiving an elongated continuous sheet of paper, the paper passing on the support surface from the supply reel to the take-up reel, characterized by driving means (46) for rotating the receiving spool (30) in the winding direction to pull the paper (34) from the supply spool (26) and advance it the support surface, and - means (64, 90, 120) for feeding these drive means (46) so as to advance the paper of the sheet continuously on the support surface at a speed is predetermined independently of the diameter of the take-up spool (30) The plotter of claim 1, further characterized in that the means for supplying the drive means (46) of the receiver coil (30) comprises: means (64) for measuring the actual speed of travel of the paper relative to the support surface (14) and for producing a signal depending on the actual speed of the paper, - means (170) for delivering a reference speed signal of the paper, - means (168) for comparing the signal the actual speed of the paper to the paper reference speed signal so as to produce an error signal, and - means (172) operating in response to this error signal for feeding the drive means (46). ) of the receiver coil in the direction of the reduction of this error signal.   The plotter of claim 2, further characterized in that the means (64) for measuring the speed of the paper relative to the support surface (14) and for producing a signal representative of the actual speed of the paper comprises: - a measuring wheel (66) rotatably mounted on an axis perpendicular to the direction of movement of the paper above the support surface and may, at its periphery, come into contact with the paper so as to be driven around its axis when the paper moves relative to the support surface, - means (76, 78, 80, 82), associated with this measuring wheel, for producing electrical pulses in response to the rotation of this wheel about its axis , the intervals between the successive rising edges of the pulses each corresponding to a fixed, fixed angular rotation of this wheel, and - means (166) for converting these pulses of   to give said actual paper speed signal.   The plotter of claim 3, further characterized in that the measuring wheel (66) comprises: a plurality of optically transparent zones (76) alternating around an axis which is the same as the axis rotation of the measuring wheel, with a plurality of optically opaque zones (78), and - a light source (80) and a photodetector (82), arranged on either side of the wheel so that the photodetector produces an electrical pulse output signal resulting from the chopping, by the optically transparent and opaque zones of the measuring wheel, of the path   light from the light source to the photodetector.   The plotter of claim 1, further characterized in that the drive means for rotating the take-up spool comprises: a DC drive motor (46) whose speed is such that when fed continuously, it drives the take-up spool in the winding direction by feeding the paper onto the support surface at a speed greater than said predetermined speed even when the take-up spool is of minimum diameter, and means (120) for controlling the speed of this motor by pulse width modulation of the voltage which is applied.   The plotter of claim 1, further characterized by means (136) for reversing the driving direction of the take-up spool (30) to unroll a portion of the long continuous sheet of paper (34). ) that had been previously wound on during the rotation of the take-up reel in the direction of winding. The plotter of claim 6, further characterized in that: the drive means for rotating the take-up spool comprises a DC drive motor (46) powered by a DC voltage of polarity given, so as to rotate the receiver coil in the winding direction, and - the means (136) for reversing the driving direction of the receiver coil comprises means for reversing the polarity of the voltage applied thereto. motor, so   to turn it in the opposite direction.   The plotter of claim 1, further characterized in that the drive means comprises: - a DC drive motor (46) having terminals between which a DC supply voltage can be applied, means (90) for producing a paper feed START signal; means (176), operating in response to this START signal, for first feeding the drive means by application of a a DC supply voltage between the input terminals of the motor to feed the paper continuously over the support surface at said predetermined speed, - means for measuring the feed movement (64, 176), for measuring the length of paper that has been advanced since the beginning of the advance movement, - means (172) operating in response to these means   measuring the movement in advance, to modify the feed-   of the drive means to slow down the paper feed speed after a first given length of paper has been advanced since the beginning of the feed movement, and - means (172) operating response to the means of   measure the movement in advance, to interrupt the feeding   driving means for stopping the advance movement of the paper above the support surface after a given second length of paper has been advanced since the start of the feed movement, these means for interrupting the supply of the driving means comprising means which, in response to the measurement, by the means for measuring the advance movements, of a movement in advance of said second length of paper since the beginning of the movement of in advance, terminate the application of the voltage between the input terminals of the drive motor and short-circuit these input terminals so as to obtain a dynamic brake effect from the motor. The plotter of claim 8, further characterized by a motor control stage (120), comprising: a first input conductor receiving signals BRAKING and BRAKING, a second input conductor receiving signals MOTOR and MOTOR, - a processor (90) delivering the signals BRAKING and BRAKING to this control stage by the first input conductor and delivering to it the signals MOTOR and MOTOR by the second input conductor, this stage of pilot operated to start the engine by not applying a supply voltage   between the input terminals of this motor only when it appears   simultaneously sense the MOTOR and BRAKE signals on the input leads, and so as to short-circuit the motor input terminals when the BRAKE signal appears, on the second input lead, at the input of the pilot stage.   The plotter of claim 9, further characterized in that: - the MOTOR signal corresponds to a ground and the MOTOR signal corerspond to an airing of the first input lead, and the signal BRAKING is a venting and the BRAKING signal is grounding the second input lead, so that the power to the motor is terminated as soon as one or the other of the two leads, or both drivers, are in the air.