GB2164901A - Reading or writing apparatus - Google Patents

Abstract

A read head or a pen 12 is arranged to rotate in a curved path, e.g. spiral or circular. In the arrangement shown the pen 12 moves about an axis II-II which in turn rotates about another axis I-I fixed relative to a medium 4 which is to be written on. The pen 12 follows a curved path across the medium 4, producing less stress in the apparatus than is associated with conventional apparatus which follows discontinuous linear motion. The pen 12 is activated at desired positions along its path of movement. <IMAGE>

Description

SPECIFICATION Apparatus for scanning a medium This invention relates to apparatus, for scanning a medium, which is capable of writing and/or reading.

Previously known scanners include a scan head for reading or writing which moves in a straight line motion relative to a medium to be read or written on. The direction of motion is changed at the end of a line and thus the head and/or medium must undergo discontinuous motion, by which it is meant that the moving part must decelerate, stop and then accelerate.

This discontinuous motion may involve deceleration at the end of a line, stopping, and then acceleration in the opposite direction along the next line, but more typically the motion is one which includes a flyback period, involving extremely rapid acceleration, travel velocity and deceleration, to return to the same point for the start of each line.

There are disadvantages associated with such previously known apparatus in which components undergo discontinuous motion.

The rapid change in direction of movement and the high deceleration and acceleration experienced because of this results in large mechanical stresses being momentarily incurred by the apparatus, which must thus be of robust construction to withstand them. Also vibration may be a problem and a certain degree of looseness, or backlash, may develop in the apparatus, reducing the accuracy in positioning the head relative to the medium. A further disadvantage is that the speed with which the medium is moved relative to the head must be restricted to limit the stresses produced to acceptable levels, and delays are introduced by the need to stop at the end of each line and change direction.

According to a first aspect of the invention there is provided apparatus for scanning a medium, comprising a scan head arranged to move relative to the medium in a predetermined path, only one of the scan head and the medium being movable, said one's motion being non-discontinuous in a curved path.

The scan head may be a read or write head, or may combine the two functions. The relative motion of the scan head and the medium can be arranged so that the head moves over a substantial part of the medium to achieve high resolution.

By arranging that the motion follows a curved path the stresses experienced by the apparatus are reduced, since the changes in velocity may be less, compared with those of conventional scanners which inevitably require repeated stopping and starting of the scan head or medium movement. Thus the speed of the motion may also be increased. It is preferred that the curved path is continuously curved, but it may consist of curved sections linked by straight sections. A continuous curved motion reduces stresses to a much lower level for a given speed of movement than would be the case for apparatus using only a straight line motion. Preferably also the curved path has a constant degree of curvature, but it could consist of sections having different curvatures.

According to a second aspect of the invention there is provided apparatus for scanning a medium, comprising a scan head arranged to move non-discontinuously in a predetermined path relative to the medium, the medium being fixed in position, and motion of the scan head being in a continuously curved path about an axis fixed relative to the medium. Preferably the actual motion is in a curved path which curves in one sense only. In this Specification the term 'sense' is used to describe the direction in which the motion of the scan head curves, to the right or to the left. By arranging, for example, the scan head to travel in a curved motion which is directed always to the left only, or to the right only, the apparatus may be made mechanically simple and it enables higher speeds to be obtained.Also delays which are present in apparatus using discontinuous straight line motions because of the time required to change direction at the end of a line are eliminated, vibration is minimized and accuracy tends to be increased.

A plurality of scan heads may be included and arranged to rotate about an axis in respective concentric paths, such as those illustrated in Fig. 1, where the paths are denoted by 1 and the medium by 2.

An alternative is to arrange the scan head to rotate about an axis at a variable distance from it, for example the distance could be increased as the head moves to obtain a spiral path like that shown in Fig. 2.

Apparatus employing optical techniques, where a light beam is directed across a light sensitive medium for example, may also advantageously utilize the invention, since changes in current direction and hysteresis may be reduced.

According to a third aspect of the invention there is provided apparatus for scanning a medium, comprising a scan head arranged to rotate at a constant distance about a first axis which is rotatable at a constant distance about a second axis fixed relative to the medium, such that the scan head moves in a curved path. It is preferred that in operation, the speed of rotation about the first axis is greater than that about the second axis. Preferably the distance between the scan head and the first axis is smaller than or equal to the distance between the first and second axes. Preferably the curved path lies in a plane substantially parallel to the plane of the medium, and these two planes may coincide where the medium is arranged to move, and it is preferred that the medium is flat.

Preferably inhibition means is included to prevent the scan head operating for part of its path. Thus where the head follows a path which takes it over an area of the medium more than once, or which covers it by a greater amount than is demanded by the resolution required, operation of the head may be inhibited to reduce redundancy.

The invention is now further described by way of example with reference to the accompanying drawings, in which: Figure 3 is a schematic perspective view of one apparatus in accordance with the invention; Figures 4 and 5 are explanatory diagrams relating to the apparatus of Fig. 3, and Figure 6 is a schematic perspective view of another apparatus in accordance with the invention, with like references being used for like parts throughout.

With reference to Fig. 3, apparatus for printing includes a circular plate 3 of radius r1 on which a medium which is to be written on is located. In this case the medium is a sheet of paper 4. A framework consisting of two upstanding portions 6 and 7 and a cross piece 8 is clamped across a diameter of the plate 3, the cross piece 8 being spaced from and parallel to the surface of the paper 4.

A member 9 extends through the cross piece 8 and is aligned with the centre of the plate 3 along an axis l-l. A first arm 10 is attached to one of its ends to the member 9 for rotation about the axis l-l. A second arm 11 is attached to the other end of the first arm 10 for rotation about another axis ll-ll which is parallel to the axis l-l. A write head consisting of a pen 12 is fixed to the second arm 11 and is thus rotatable about the axis ll-ll. The pen 12 is located at a radius r2 from the axis ll-ll which is half of the radius r1.

A drive motor and position encoder are contained within a first housing 13 at the junction of the first and second arms 10 and 11, and another drive motor and position encoder within a second housing 14 about the member 9 at the cross piece 8. Power and control signals are passed to the motors and position encoders via a line 15.

In operation, the second arm 11 is driven about the axis ll-ll such that the pen 12 follows a circular path about it, and the first arm is driven at a slower speed about the axis l-l.

Part of the resulting path followed by the pen 12 is illustrated in Fig. 4. Several revolutions about the axis ll-ll and part of a revolution about the axis I-I are shown as having taken place to obtain a series of intersecting circles.

The earlier revolution undergone about axis ll-ll is denoted as 16 and the later one 17, intermediate parts of the path also being shown. Where printing is required at any position along the path the pen 12 is activated.

As can be seen from Fig. 4, the area of the paper at the circumference of the main circle of radius r1 and 'at its centre has a higher degree of coverage by the path than other parts, and thus, for a given resolution, for the total area to be covered there is some redundancy at these parts of the paper. The control signals may include inhibition signals so that the pen 12 is not activated over a part of the paper 4 more densely covered by its path. In any case the pen 12 is only arranged to operate for the first half of each smaller circle of radius r2 of its path, since greater resolution is not required. Parts of the path where the pen 12 is inhibited are shown as broken lines.

If an image which is stored in cartesian form is to be printed on to the paper 4 it must be translated into polar form. This can be done using the following relationship:- x=r2 (cos l-cos (()1+O2)) and y=r? (sin ()1in (()l+f)2ìì where ()1 is the angle between the first arm 10 and the x-axis and ()? is the angle between the first and second arms 10 and 11, as illustrated by Fig. 5.

The speed of rotation about the axis I-I may be greater than that about the axis ll-ll in which case the path followed by the pen 12 is a spiral.

Although the apparatus shown in Fig. 3 is a printer a read device may be similarly constructed except that a read head is substituted for the pen 12.

Another embodiment in the invention includes an arm 18 which rotates about the axis I-I as shown in Fig. 6. A plurality of read heads 19 are distributed along the arm 18 such that as the arm rotates each of them follows a circular path to give a concentric series of paths, as shown in Fig. 3.

An alternative embodiment (not shown) has only one read or write head which is carried by an arm. The arm is arranged to rotate about an axis and as it does so the read or write head is arranged to move along the arm so that the radius of its path about the axis increases or decreases and hence follows a spiral path.

Claims (14)

1. Apparatus for scanning a medium, comprising a scan head arranged to move relative to the medium in a predetermined path, only one of the scan head and the medium being movable, said one's motion being non-discontinuous in a curved path.

2. Apparatus as claimed in claim 1 and wherein the curved path is continuously curved.

3. Apparatus for scanning a medium, com prising a scan head arranged to move nondiscontinuously in a predetermined path, relative to the medium, the medium being fixed in position, and motion of the scan head being in a continuously curved path about an axis fixed relative to the medium.

4. Apparatus as claimed in claim 1, 2 or 3 and wherein the curved path curves in one sense only.

5. Apparatus for scanning a medium, comprising a scan head arranged to rotate at a constant distance about a first axis which is rotatable at a constant distance about a second axis fixed relative to the medium, such that the scan head moves in a curved path.

6. Apparatus as claimed in claim 5 and wherein in operation the speed of rotation about the first axis is greater than that about the second axis.

7. Apparatus as claimed in claim 5 or 6 and wherein the distance between the scan head and the first axis is smaller than or equal to the distance between the first and second axes.

8. Apparatus as claimed in any preceding claim and wherein the curved path lies in a plane substantially parallel to the plane of the medium.

9. Apparatus as claimed in any preceding claim and wherein the medium is substantially flat.

10. Apparatus as claimed in any preceding claim and including inhibition means to prevent the scan head operating for part of its path.

11. Apparatus as claimed in claim 1, 2, 3 or 4 and including a plurality of scan heads arranged to rotate about an axis in respective concentric paths.

12. Apparatus as claimed in claim 1, 2, 3 or 4 and wherein the scan head is arranged to rotate about an axis at a variable distance from it.

13. Apparatus substantially as illustrated in and described with reference to Fig. 3 of the accompanying drawings.

14. Apparatus substantially as illustrated in and described with reference to Fig. 6 of the accompanying drawings.