GB2043885A - Pulse Generator - Google Patents

Abstract

A pulse generator has a disc rotor 2 with a circumferential ring of holes 4 separated by bars 5 for co-operating with an opto-electronic device 3 for generating pulses in certain angular positions of the rotor 2. The rotor 2 can be easily rotated by hand and restrained in certain set angular positions by means of magnetic poles and closely spaced from a second ring of holes 9 and bars 10, defining alternate regions of low and high permeability in a magnetic circuit including the poles and the disc. <IMAGE>

Description

SPECIFICATION Pulse Generator This invention relates to a pulse generator for example a pulse generator having a rotor capable of being rotated by hand for co-operating with a sensor to generate pulses, for example for quasicontinuous or fine tuning of a frequency synthesizer.

Pulses can be generated as the rotor, which conveniently comprises a disc, rotates past the sensor which might be a mechanical device, or a magnetic or capacitive device, or an optoelectronic device, for example consisting of a light emitting diode and a photo-sensitive semiconductor on either side of a disc rotor having a circumferential ring of holes through which light can pass from the light emitting diode to the photo detector in certain positions of the disc rotor.

It is desirable that the rotor can be very easily turned by hand into any one of a wide range of positions, while yet it is desirable that once positioned, the rotor should not be easily displaced from its angular position due to external knocks or vibrations. Where the device is used for a continuously tunable frequency synthesizer such a movement of the rotor, even a small one, would upset the chosen frequency setting.

According to the present invention, a pulse generator having a rotor capable of being rotated by hand, and a senser arranged to generate pulses in response to the rotor being in certain angular positions, includes also a magnetic restraining device capable of restraining the rotor against movement away from certain angular positions without physical contact between the rotor and the restraining device.

Thus, there may be on the rotor a ring of local regions of alternately high and low magnetic permeability wich move in relation to a magnetic pole as the rotor is turned, the regions of high permeability being aligned with the pole in the certain angular positions in which it is desired to be able to retain the rotor.

There can be a narrow air gap between the pole and the surface of the rotor, which is sufficient to provide restraining force against rotor displacement due to unwanted vibrations, while yet it is easy for the user to reset the rotor by hand against the restraint. He can also feel the rotor lock into different positions of restraint.

This arrangement in which there is no physical contact between the rotor and the restraining device is a considerable improvement over such a device as a mechanical pin which is inserted by the operator both in the rotor and in a fixed part after he has set the rotor position.

In a preferred form of the invention, the regions of different magnetic permeability are provided by a ring of alternate holes in the rotor, and bars between holes, and the restraining device has a pole corresponding to a bar, so that the rotor can be restrained in any position in which a bar is aligned with the pole.

An embodiment of the invention will now be described by way of example, and with reference to the accompanying drawings, in which: Figure 1 is a plan view of a pulse transmitter, Figure 2 is a section along the line Il-lI in Figure 1; and Figures 3a and 3b show enlarged details of the magnetic restraint along the line Ill-Ill of Figure 1.

The figures show a pulse transmitter which operates on the opto-electronic sensing principle, and is particularly suited to the quasi-continuous tuning of a frequency synthesizer in a superheterodyne receiver. The pulse transmitter illustrated consists of a rotary part turned by hand by an adjusting knob 1, the rotary part being in the form of a disc 2 which is connected to the adjusting knob 1 by a spindle 6, the disc 2 being associated with an opto-electronic sensing device 3. The disc 2 has a first ring of punched holes 4 with intermediate bars 5 with which the optoelectronic sensing device 3 is associated.As the disc 2 is turned about the spindle 6 the beam path of opto-electronic sensing device 3 is alternately interrupted by bars 5 and unobscured by holes 4, thus producing, through the sensing device the desired pulse train dependent on direction of rotation, which can be used, for example, to advance the counter of a frequency synthesizer.

The spindle 6 is borne by a thrust and journal bearing 7. The disc 2 also carries a mass 8 to add inertia to make fast spinning possible.

A further ring of rectangular holes 9 with intermediate bars 10 is formed on disc 2. Disc 2 is of a ferro-magnetic material. The ring of holes 9 and bars 10 is associated with two pole-pieces 11 and 12 of a magnetic yoke 13 carrying at its centre a permanent magnet 14. The magnetic yoke 1 3 with permanent magnet 14 is so arranged with respect to the disc 2, that there is between the permanent magnet 14 and the centre of the disc 2 (when not interrupted by punchings) the narrowest possible air gap 15, and between the front face of pole-pieces 11, 1 2 and the disc 2 there is also the narrowest possible air gap 1 6 as shown in Figure 2.The magnetic circuit is completed through air gaps 15, 16 and disc 2 in the direction of the lines of force as arrowed in Figure 2, whether or not a hole 9 or a bar 10 is opposite the front face of the pole-piece, as explained in more detail with reference to Figure 3.

To magnify the force of the magnetic flux, each pole-piece 11, 1 2 is provided with several poletips 18, as shown in the enlarged illustrations in Figures 3a and 3b. Each pole-piece is about as wide as a bar 10 on the disc, and the distance between adjacent pole-tips 1 8 corresponds to the distance between holes 9.

If the disc assumes the position illustrated in Figure 3a, with pole-tips 1 8 exactly opposite the respective bars 1 0, the region which the magnetic flux flows through is the one of greatest magnetic permeability, and thus the maximum magnetic retaining force acts on the disc to hold the disc in the position illustrated in Figure 3a, with a force dependent upon the strength of magnet 14.If the disc is turned out of the position of Figure 3a, to the position of Figure 3b, in which a hole 9 is opposite a pole-tip 18, the region which the magnetic flux flows through is one of minimum magnetic permeability, and thus force between pole-pieces and disc acts to rotate the disc away from this position towards the stable position as Figure 3a where the lines of force are shortest, The rings of holes 9 and bars 10 may be formed simultaneously on the actual coding disc of the pulse transmitter. This is particularly advantageous for such pulse transmitters in which, say, sixty or more holes are in each ring for it is then very easy to produce the exact angular positions. In many cases the ring of magnetic restraining devices can be on a separate component, e.g. on a flywheel or directly on the hub of the spindle, for example if a disc is not used as the rotary part.The successive regions of varying magnetic permeability of the restraining device can obviously be established other than by a series of holes 9 and bars 10, e.g. by corresponding bosses or by direct formation of corresponding varying magnetic domains in the disc concerned. The different magnetic domains could be developed on the circumference of a cylindrical part of a commutator outside of which is arranged a corresponding permanent magnet.

In pulse transmitters with pulses produced magnetically, in which corresponding permanent magnets are attached to the rotary part at predetermined angular positions, the additional magnetic restraint may be external to this rotary part.

In the figures, several simultaneously effective pole-tips 1 8 are provided to amplify the magnetic retaining forces, because the restraining positions are evenly divided around the disc. In many cases of course a single pole-piece suffices, particularly when the bars 10 are broad.

Also, two diametrically opposed pole-pieces 1112 as illustrated may be replaced by a single pole-piece 1 The symmetrical construction of pole-pieces of the embodiment illustrated balances the applied magnetic forces on the disc and spindle.

The restraining forces depend upon the strength of the permanent magnet 14, the material of the disc 2, the size of the air gaps 1 5 and 1 6 and the nature of the gap-defining surfaces. A desired restraining effect can be achieved by adjustment of these parameters.

In the example described there is a ring of holes 9 in addition to the ring of holes 4 for the opto-electronic pulse producing and sensing device 3. It would be possible to use the holes 4 and bars 5 for the restraining device as well as for the output pulses with the device 3 and the polepieces 11 and 1 2 at different angular positions.

Every bar 5 of the ring defines a corresponding restraint position, i.e. the disc can be restrained in any of the possible angular positions of the pulse transmitter. In a modification there may be a corresponding magnetic restraint position only for every second, third or even every fifth or tenth bar 5 of the outer ring, so that the disc can not be restrained in every possible angular position corresponding to a hole 5, but only in uniformly divided positions around the circumference of the disc. If, for example, the pulse transmitter is used to produce additive pulses for a quasi-continuous tunable frequency synthesizer and if each single angular position of the outer ring represents a frequency step of 1 Hz. the disc is only restrained at each fifth bar 5, this signifies that the disc is only restrained at 5 Hz. intervals and intermediately can be continuously rotated unrestrainedly.

Claims (12)

Claims

1. A pulse generator having a rotor capable of being rotated by hand and a sensor arranged to generate pulses in response to the rotor being in certain angular positions, and including also a magnetic restraining device capable of restraining the rotor against movement away from certain angular positions without physical contact between the rotor and the restraining device.

2. A pulse generator as claimed in Claim 1 in which the restraining device includes a permanent magnet having at least one pole closely spaced from the surface of the rotor.

3. A pulse generator as claimed in either of the preceding claims in which the rotor has a circumferential ring of regions alternately of high and low magnetic permeability.

4. A pulse generator as claimed in Claim 3 in which the regions are provided by holes in the rotor and bars between adjacent holes.

5. A pulse generator as claimed in any of Claims 2-4 in which the magnet has two poles closely spaced from diametrically opposite parts of the rotor surface.

6. A pulse generator as claimed in any of Claims 2-5 in which the or/each magnet pole is sub-divided into circumferentially spaced pole tips with a pitch corresponding to the pitch between the alternate regions of the rotor.

7. A pulse generator as claimed in any of Claims 2-6 including a central permanent magnet and a yoke leading from the magnet to the pole or poles.

8. A pulse generator as claimed in any of the preceding claims including Claim 4, in which the width of a bar between adjacent holes is equal to the width of a pole or a pole tip.

9. A pulse generator as claimed in any of the preceding claims in which the rotor has a circumferential ring of holes for generating pulses in response to the rotor being in certain angular positions.

10. A pulse generator as claimed in Claim 9 in which there is a second ring of holes defining the certain angular positions in which the rotor can be restrained.

11. A pulse generator as claimed in Claim 9 in which the magnetic restraining device is anguiarly spaced from the sensor and uses the same ring of holes for providing the magnetic restraint, as are used for generating pulses.

12. A pulse generator arranged substantially as herein specifically described with reference to the accompanying drawings.