GB2066742A - Chart recorder - Google Patents

Abstract

A chart recorder in which the writing head 14 is rotatable by a stepper motor 16 to position any one of several writing tips 20 over the paper. The stepper motor 16 is mounted on the same carriage as the writing head for movement relative to the paper. <IMAGE>

Description

SPECIFICATION Chart recorder The present invention relates to a chart recorder.

As is well known, a chart recorder is a device which provides a permanent trace on a recording medium showing the variations of a measured parameter with time. The recording medium, for example paper, is moved past a writing head which itself moves transversely with respect to the paper in dependence upon the measured parameter.

Chart recorders are known which plot a plurality of parameters simultaneously using different heads which are staggered from one another in a suitable manner.

The present invention seeks to provide a simplified chart recorder for recording traces of a plurality of parameters.

In accordance with the present invention, there is provided a chart recorder for producing a record of a plurality of parameters, having a writing head movable transversely with respect to a recording strip, wherein the writing head includes a rotatable holder having a plurality of writing points circumferentially spaced about its periphery and a motor movable with the holder for rotating the holder to select a writing point in dependence upon the parameter being recorded.

The traces are in the form of interrupted lines each line segment being produced by actuating the head to bring the writing point into contact with the recording medium when the transverse position of the writing head with respect to the recording strip corresponds to the value of the parameter being recorded.

Conveniently, the writing points may be the tips of felt tipped pens located in the holder, the pens being of different colours.

Conveniently, the motor may be a stepper motor having a plurality of coils the axes of which are parallel to the rotational axis of the holder and a permanent magnet rotor having diammetrically opposed arcuate coplanar north and south poles facing the axial ends of the coils. To provide still more accurate angular positioning of the holder, it is advantageous for the holder to include recesses arranged to co-operate with a detent to ensure that the holder can adopt predetermined angular positions.

The pole faces may each conveniently extend over an angle sufficient to align each pole face with a plurality of coils so as to increase the torque applied to the rotor.

In order to actuate the writing head to produce a marking on the recording strip, the stepper motor may conveniently be pivoted on a carriage transversely slidable with respect to the strip and an electro-magnet may be provided to rotate the motor with respect to the carriage to cause the selected writing point to mark the recording strip.

The position of the writing head with respect to the recording strip may be determined by means of a closed feedback loop comparing the actual position of the writing head as determined by an analogue sensor with the signal to be recorded.

Alternatively, a digitally operating open loop may serve to position the writing head in dependence upon the magnitude of the parameter to be recorded.

The parameters may be charted on the recording strip in a predetermined order but preferably the order is selected in each line in dependence upon the magnitude of the parameters in a preceding line whereby to minimise the movement of the writing head relative to the strip.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a section through a chart recorder in accordance with the invention, and Figure 2 is a section through a stepper motor incorporated in the chart recorder of Figure 1.

The chart recorder in Figure 1 comprises a housing 10 which contains a paper feed mechanism generally designated 12 in which paper is guided steadily past a writing head 14 which is movable transversely with respect to the paper. The writing head 14 includes a stepper motor 16 which serves to drive a pen-holder 18 carrying six felt tipped pens, the tips of which are designated 20. The tips 20 are circumferentially spaced about the periphery of the holder 18. The motor 16 and the pen holder 18 are supported by a carriage 22 which is guided for transverse movement with respect to the paper by means of a pair of rails 24. The displacement of the carriage 22 is effected by means of a motor 26 connected to the carriage by means of a cord 28 guided over pulleys 30.

The motor 16 is pivotable relative to the carriage 22 about an axis 32, pivoting being effected by actuation of an electro-magnet 34.

When actuated, the electro-magnet 34 serves to rotate the motor 16 and the pen holder 18 counterclockwise as viewed in Figure 1 to cause the relevant writing tip 20 to come in contact with the paper. An electrical measuring unit, not shown, is also incorporated in the housing 10 and determines when the transverse position of the writing head 14 corresponds with the magnitude of a parameter to be recorded to cause actuation of the electro-magnet 34. The electrical unit may comprise an amplifier followed by a comparator for comparing the actual position of the writing head with the position corresponding to the magnitude of the parameter to be recorded and serving to apply an error signal to the motor 26.

Alternatively, the control of the position of the writing head may be effected by means of an open loop wherein the position of the motor 26 may, for example, be digitally controlled in dependence upon the magnitude of the parameter to be recorded.

As previously stated, the pen holder 18 carries six circumferentially spaced pens each of a different colour and each intended to represent a different parameter. The stepper motor 16 serves to position the appropriate pen corresponding to the next parameter to be recorded. The stepper motor 1 6 is shown in more detail in Figure 2 and comprises six separate coils 40 the axes of which are parallel to the axis of rotation of the holder 18.

The rotor 42 comprises two magnets 44 in the form of semi-circular segments mounted on a circular plate 46 connected to the output shaft 48 of the stepper motor. Three of the electro-magnets 40 are supplied with a current of a first polarity whilst the remaining three are fed with a current of the opposite polarity. This results in the rotation of the rotor 42 to align the permanent magnets 44 with the oppositely poled electro-magnets 40. By energising three electro-magnets of any one polarity at a time, a substantial torque may be developed by the motor.

To ensure precise positioning of the pen holder 18, the base of the pen holder includes six recesses 50 of which only one is shown in Figure 1 in dotted lines. A detent 52 projects from the carriage 22 and engages one of the recesses 50 when the holder 18 is rotated so as to provide precise positioning of the felt tip 20.

The order of marking of the different colours on the paper may be fixed but this would result in several traverses of the paper by the writing head during each scan line. To avoid unnecessary movement of the writing head, the colours are selected in the order in which marking took place in the preceding scan line. This is achieved electronically by means of a memory circuit incorporated in the chart recorder and not illustrated in the drawings.

Claims (9)

1. A chart recorder for producing a record of a plurality of parameters, having a writing head movable transversely with respect to a recording strip, wherein the writing head includes a rotatable holder having a plurality of writing heads circumferentially spaced about its periphery and a motor movable with the holder for rotating the holder to select a writing point in dependence upon the parameter being recorded.

2. A chart recorder as claimed in Claim 1, wherein the writing heads are the tips of felt tipped pens located in the holder, the pens being of different colours.

3. A chart recorder as claimed in Claim 1 or Claim 2, wherein the motor is a stepper motor having a plurality of coils the axes of which are parallel to the rotational axis of the holder and a permanent magnet rotor having diammetrically opposed arcuate coplanar north and south poles facing the axial ends of the coils.

4. A chart recorder as claimed in any preceding Claim wherein the stepper motor is pivoted on a carriage transversely slidable with respect to the strip and an electro-magnet is provided to rotate the motor with respect to the carriage to cause the selected writing point to mark the recording strip.

5. A chart recorder as claimed in Claim 4 as appended to Claim 3, wherein at least one recess and at least one detent are provided on the holder and the carriage to ensure that the holder can only adopt predetermined angular positions during writing.

6. A chart recorder as claimed in any preceding Claim, wherein the position of the writing head with respect to the recording strip is determined by means of a closed feed-back loop comparing the actual position of the writing head as determined by an analogue sensor with the signal to be recorded.

7. A chart recorder as claimed in any one of Claims 1 to 5, wherein a digitally operating open loop is provided to position the writing head in dependence upon the magnitude of the parameter to be recorded.

8. A chart recorder as claimed in any preceding Claim, wherein the order of recording of the parameters is selected in each line in dependence upon the magnitude of the parameters in a preceding line so as to minimise the movement of the writing head relative to the recording strip.

9. A chart recorder constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.