GB1590517A - Device for scanning and/or line jumping in opto-electronic scanning apparatus - Google Patents

Description

(54) DEVICE FOR SCANNING AND/OR LINE JUMPING IN OPTO-ELECTRONIC SCANNING APPARATUS (71) We, ELTRO G.m.b.H. GESELL SCHAFT F(YR STRAHLUNGSTECHNIK, a German limited liability company, of 6900 Heidelberg 1, Kurpfalzring 106, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the electromagnetic excitation of an oscillating optical element, for example an oscillating mirror which deflects an incident beam onto a detector line.

A line jumping device for opto-electronic scanning apparatus is known from German Patent Specification No. 1,803,609, comprising a rotating disc with zones of different beam refraction. This device is described only with reference to its optical/mechanical parts but without indicating a way of achieving its control function. Moreover, the structure of its disc is relatively complex and is only intended for deflection and not for scanning as well.

In addition, a scanning method is known from German Patent Specification No.

2,226,372 in which the image of an object is set in rotation by means of a pentaprism and is then scanned linearly by means of a polygonal prism. In this case also there is no indication as to how control of the movable prism components should be carried out during a line jump.

It is an! dbject of the invention to provide an apparatus by which the cleanest possible path function of movable scanning and deflecting elements, particularly step func tions; can be carried out. According to this invention apparatus for the electromagnetic excitation of an oscillating optical element comprises an electric motor having a movable part and a stationary part, the movable part being attached to the optical element, wherein the said parts are interconnected by at least one cross flexure bearing to resist relative motion between the parts, the motor being connected in an electrical feedback circuit operable to control movement of the movable part thereby to control the deflection of light rays by the optical element. In this way it is possible to preset a required control function with sinusoidal, saw-tooth or rectangular characteristics, and to put these into effect under stable electrical conditions. The connection of the "stator" and the "rotor" via cross flexure bearings makes it possible to preserve a specific null position and, if necessary, to deflect the movable part through small angles of rotation which correspond both to the layout of the bearings and also to the line-tipping movement. With regard to the movable components and the effective electromagnetic forces, there is moreover an advantageous centering effect.

As for the state of the time constants, that of the spring-mass system amounts according to dimensions to around 50 ms and that of the movement sequence to around 3.5 ms.

The invention also includes the layout of the closed control circuit which contains a unit for the required path function, to which-in the transmission direction of the signal another unit which compares the desired function may be connected; via a subsequent amplifier the result controls the motor which is connected via a mechanical axis to a path receiver which in turn produces the actual function via another amplifier. By this means, firstly a correct stepping function is possible, with clear separation of the separate steps, as is required for a tipping motor. In other words: a control circuit of this kind makes it possible to control the abovementioned motor in such a way that the preset function, which can in principle be any time-path function, is carried out exactly.

Basically, it does not matter which motor part is designed to be stationary and which can be rotated. Simply from the point of view of the power supply leads, it would appear to be more expedient in view of the projections for the "rotor" equipped with the coils to be stationary and for the "stator" which carries the mirror to be movable.

From the constructional point of view it is advantageous if, arranged concentrically to the axis of rotation on each side of the stationary "rotor", there is a holder for the cross flexure bearings, and if, attached to the movable "stator", there is a mirror mounting which holds the mirror at an inclination to the axis of rotation.

An advantageous method for operating the mirror described above can be such that the same mirror is used both for scanning and for line jumping, being tipped in continuously progressing steps from one detector to another for line jumping, and swivelled with the aid of an additional operating magnet in the direction perpendicular to the tipping movement, for scanning, which precedes each deflection of the beam.

Finally, the invention may provide for the use of an oscillatory mirror, a flat plate prism, a polygonal wheel or a reflecting prism, for scanning. The latter is particularly suitable in the convergent beam path and with a linear motor.

The invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a section of device in accordance with the invention, with an electric motor which carries a tipping mirror; Figure 2 is a block circuit diagram including a closed control circuit; Figure 3 shows a motor according to Figure 1 with a flat face plate in place of the tipping mirror; Figure 4 shows schematically a motor according to Figure 1 with an oscillatory mirror in place of the tipping mirror; Figure 5 shows at a the characteristic step function of the tipping mirror, and at b a random step function of the tipping mirror; Figure 6 shows a prism which carries out a linear scanning movment; and Figure 7 shows a tipping mirror which is similar to those shown in Figures 1 and 4, which is designed to carry out, in addition to the tipping movement, a scanning movement perpendicular to the tipping movement.

Referring to Figure 1, an electric motor 1 comprises a stationary rotor 2 and a movable stator 3. The rotor carries coils 4 and also has, coaxial with the axis of rotation 5, a holder on either end for two cross flexure bearings 7 which form the connection with the movable stator 3. The latter carries a permanent magnet 8 which is similarly anchored concentric to the axis 5 by screws 9. In addition, on one end of the stator there is a mirror mounting 10 attached concentically; this holds a tipping mirror 11 at an inclination to the axis of rotation, in the present case at 45=.

The tipping mirror deflects a beam which strikes it in the direction of the arrow 31, so that it is reflected in the direction of the arrow 30 onto the detector line, not shown. In this case, the direction of the arrow 30 also represents the projection of the tipping plane of the mirror 11. 12 designates a power supply connection, and 13/14 represent a path receiver, for example, a capacitive path receiver, the part 13 of which is stationary and the part 14 of which is movable. In another embodiment, not shown, a reversed version with a stationary stator and a movable rotor is also possible.

Figure 2 shows a closed control circuit in which the required function, which in the present case is the path function, is inserted into a unit 15. In the transmission direction of the signals, a unit 16 follows in which the path function is corrected so that at its output 17 the control function required for the motor I is available, and is then further amplified in an amplifier 18. The motor I connected to earth 19 is connected via a mechanical axis 20 to the path receiver 13, 14 and rotates the part 14, thus producing the actual function. The latter is then passed through an amplifier 21 and becomes available for the above-mentioned correction. If this and the function from the unit 15 have the same dimensions then subtraction would produce the amount "zero" at the output 17.

In practice there is a small difference between the required function and the actual function, according to the control amplification, amounting to 1%, for example, which is sufficient to control the motor after appropriate amplification.

Figures 3 and 4 each show the tipping mirror 11 is replaced by a component which serves for beam scanning. In Figure 3 this is a flat plate prism 22 through which a scanned beam 30' passes, and in Figure 4 it is an oscillatory mirror 23; each of plate 22 and mirror 23 has an associated mounting. However, it is also possible to use other scanning elements, such as a scanning reflecting prism 24 (Fig. 6) or a polygonal wheel, not shown.

The dashed line in Figure 6 indicates linear movement of the prism, and the path relationship varied thereby of a beam path 26, the path length of which always remains constant, in the convergent beam path of an input optical system 25. In all these cases, control is effected in the same way, if the step shape of the control function is disregarded.

Finally, Figure 7 shows another mirror 23 which can carry out both a beam deflection or line tipping movement and also a scanning movement. The line tipping movement is produced (as described above) by the motor 1 which carries out the rotary movement indicated by arrow 27. The mirror starts from the position shown in full lines. As described in connection with Figure 1, it deflects the beam, which strikes it in the direction of the arrow 31, to the direction of the arrow 30; the latter again represents the projection of the tipping plane of the mirror. The actual tipping movement of the mirror cannot be seen in this view.

An operating magnet 28 causes the scanning movement which is in a plane perpendi cular to the tipping movement. It contains a path receiver, not shown. In this instance as well, the mirror 23 starts from a start position, shown in full lines. The final positions of its deflection are shown by dashdot lines, with which the arrows 29 correspond. The latter only symbolise the reflected beam during the scanning process, whilst the arrow 30 shows both the reflection of the beam at the start position of the scanning process and also the reflection during line tipping movement.

WHAT WE CLAIM IS: 1. Apparatus for the electromagnetic excitation of an oscillating optical element, the apparatus comprising an electric motor having a movable part and a stationary part, the movable part being attached to the optical element, wherein the said parts are interconnected by at least one cross flexure bearing to resist relative motion between the parts, the motor being connected in an electrical feedback circuit operable to control movement of the movable part thereby to control the deflection of light rays by the optical element.

2. Apparatus according to claim 1 including electrical circuit means operable to produce a motor current substantially proportional to a predetermined displacement/time or rotation-angle/time function.

3. Apparatus according to any preceding claim wherein the oscillatory time constant of the optical element together with the movable part and the cross flexure bearing or bearings serving to mount the element, is large compared with the time constant of the movement function of the element and movable part.

4. Apparatus according to claim 2 wherein the feedback circuit includes a comparator having one input coupled to the said electrical circuit means to receive a signal representing a required movement function and another input coupled to the motor to receive a signal representing an actual movement function, wherein the comparator is operable to compare the required function with the actual function and to produce a correction signal at its output for controlling the motor current.

5. Apparatus according to any preceding claim wherein the motor comprises a stationary rotor having an energising winding, and a movable stator which mounts the optical element.

6. Apparatus according to claim 5 wherein the stator is mounted on the rotor by two cross flexure bearings at opposite ends of the rotor.

7. Apparatus according to any preceding claim wherein the optical element is a mirror.

8. Apparatus according to claim 7 wherein the mirror is mounted on the movable part with the mirror surface inclined relative to an axis of rotation of the movable part with respect to the stationary part.

9. Apparatus according to claim 7 or claim 8 wherein the mirror is mounted to reflect an incident beam and is pivotable about one axis by the motor to cause the reflected beam to execute a continuous sequence of line progression steps relative to a detector, and wherein the mirror is pivotable about a second axis by an additional operating magnet to cause the reflected beam to execute a scanning movement substantially perpendicular to the line progression for each step in the line progression.

10. Apparatus according to any of claims 1 to 8 including an oscillating mirror, a flat plate prism, a polygonal wheel, or a reflecting prism used for scanning.

11. Apparatus for the electromagnetic excitation of an oscillating optical element constructed and arranged substantially as herein described and shown in the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. cular to the tipping movement. It contains a path receiver, not shown. In this instance as well, the mirror 23 starts from a start position, shown in full lines. The final positions of its deflection are shown by dashdot lines, with which the arrows 29 correspond. The latter only symbolise the reflected beam during the scanning process, whilst the arrow 30 shows both the reflection of the beam at the start position of the scanning process and also the reflection during line tipping movement. WHAT WE CLAIM IS:

1. Apparatus for the electromagnetic excitation of an oscillating optical element, the apparatus comprising an electric motor having a movable part and a stationary part, the movable part being attached to the optical element, wherein the said parts are interconnected by at least one cross flexure bearing to resist relative motion between the parts, the motor being connected in an electrical feedback circuit operable to control movement of the movable part thereby to control the deflection of light rays by the optical element.

2. Apparatus according to claim 1 including electrical circuit means operable to produce a motor current substantially proportional to a predetermined displacement/time or rotation-angle/time function.

3. Apparatus according to any preceding claim wherein the oscillatory time constant of the optical element together with the movable part and the cross flexure bearing or bearings serving to mount the element, is large compared with the time constant of the movement function of the element and movable part.

4. Apparatus according to claim 2 wherein the feedback circuit includes a comparator having one input coupled to the said electrical circuit means to receive a signal representing a required movement function and another input coupled to the motor to receive a signal representing an actual movement function, wherein the comparator is operable to compare the required function with the actual function and to produce a correction signal at its output for controlling the motor current.

5. Apparatus according to any preceding claim wherein the motor comprises a stationary rotor having an energising winding, and a movable stator which mounts the optical element.

6. Apparatus according to claim 5 wherein the stator is mounted on the rotor by two cross flexure bearings at opposite ends of the rotor.

7. Apparatus according to any preceding claim wherein the optical element is a mirror.

8. Apparatus according to claim 7 wherein the mirror is mounted on the movable part with the mirror surface inclined relative to an axis of rotation of the movable part with respect to the stationary part.

9. Apparatus according to claim 7 or claim 8 wherein the mirror is mounted to reflect an incident beam and is pivotable about one axis by the motor to cause the reflected beam to execute a continuous sequence of line progression steps relative to a detector, and wherein the mirror is pivotable about a second axis by an additional operating magnet to cause the reflected beam to execute a scanning movement substantially perpendicular to the line progression for each step in the line progression.

10. Apparatus according to any of claims 1 to 8 including an oscillating mirror, a flat plate prism, a polygonal wheel, or a reflecting prism used for scanning.

11. Apparatus for the electromagnetic excitation of an oscillating optical element constructed and arranged substantially as herein described and shown in the drawings.