Tachogenerators which determine the speed and acceleration of a rotating shaft by using two counter rotating shutters

Claim 2

A tachogenerator including an input shaft coupled to a first member, means for rotating a second member at a constant speed, each member having a plurality of portions, through which light can pass, the portions being evenly spaced apart round a complete circle co-axial with the axis of rotation of that member, means for projecting a light beam through the portions of the members when, during rotation, two of the portions one on each of the members are in alignment with each other and with the light beam, the light beam having a width parallel to the plane of rotation of the members which is greater than the spacing of corresponding points in adjacent portions on that member which has the larger spacing, and light-sensitive means, positioned to receive light through portions in alignment with the light beam, and coupled to an electrical filter having a cut-off frequency below the repetition frequency of light pulses incident on the lightsensitive means when only the second member rotates.

Claim 3

A tachogenerator according claim 1 including further means for projecting a further light beam through the portions of the members when, during rotation, two of the portions one on each of the members are in alignment with each other and with the further light beam, the further light beam having a width parallel to the plane of rotation of the members which is greater than the spacing of corresponding points in adjacent portions on that member which has the larger spacing, and further light sensitive means, positioned to receive light through portions in alignment with the further light beam, and coupled to the filter.

Claim 4

A tachogenerator according to claim 2 including a plurality of optical systems each comprising two means for projecting a light beam through the portions of the members when, during rotation, two of the portions one on each of the members are in alignment with each other and with the light beam, each light beam having a width parallel to the plane of rotation of the members which is greater than the spacing of corresponding points in adjacent portions on that member which has the larger spacing, and two light sensitive means one for each light beam and positioned to receive light through portions in alignment with that light beam, the first and second members having a common axis of rotAtion, the optical system being evenly spaced round a circle co-axial with the common axis, and the light sensitive means of the optical systems being coupled to the electrical filter.

Claim 5

A tachogenerator according to claim 2 including two pulse-processing means, each coupled to one of the light-sensitive means, particular thereto, each pulse-processing means being constructed to generate a train of voltage pulses, in which each pulse corresponds to a light pulse received by the light-sensitive means coupled to that pulse-processing means, and in which the product of the duration of each voltage pulse and the voltage amplitude of the pulse has a constant value.

Claim 6

A tachogenerator according to claim 2 including a direct current source coupled to the filter, the source applying a voltage equal and opposite to that of the filter in the absence of the source, when the input shaft is at rest but the second member rotates at the constant speed.

Claim 7

A tachogenerator according to claim 2 including a differentiation circuit coupled to the output of the filter for providing a signal indicative of acceleration of the input shaft.

Claim 8

A tachogenerator according to claim 2 wherein the first and second members are discs and the portions are translucent or transparent slits in the discs.

Claim 9

A tachogenerator according to claim 2 wherein the first and second members each have the same number of portions.

Claim 10

A tachogenerator according to claim 2 wherein the means for rotating the second member is a motor and the output shaft of the motor carries a bearing for the said input shaft, the tachogenerator being such that the first and second members have the same axis of rotation.

Claim 11

A tachogenerator according to claim 9 including a casing for the motor, wherein the input shaft also has a bearing in the casing wall.

Claim 12

A tachogenerator according to claim 2 wherein the input shaft and a shaft carrying the second member are mechanically isolated from one another.

Claim 13

A tachogenerator including an input shaft coupled to a first member, means for rotating a second member at a constant speed, each member having a plurality of portions, through which light can pass, the portions being evenly spaced apart round a complete circle co-axial with the axis of rotation of that member, means for projecting a first light beam through the portions of the members when, during rotation, two such portions one on each member are in alignment with each other and with the first light beam, means for projecting a second light beam through the portions of the members when, during rotation two of the portions one on each member are in alignment with each other and with the second light beam, the light beams being diametrically opposite one another with respect to the axis of rotation of the first and second members, and each beam having a width parallel to the plane of rotation of the members which is greater than the spacing of corresponding points in adjacent portions on that member which has the larger spacing, first and second light-sensitive means positioned to receive light from the light beams through portions in alignment with the first and second light beams, respectively, and to provide two pulse trains, and means for indicating the sum of the repetition frequencies of the pulse trains.

Claim 14

A tachogenerator including an input shaft coupled to a first member, means for rotating a second member at a constant speed, each member having a plurality of portions, through which light can pass, the portions being evenly spaced apart round a complete circle co-axial with the axis of rotation of that member, means for projecting a first light beam through the portions of the members when, during rotation, two such portions one on each member are in alignment with each other and with the first light beam, means for projecting a second light beam through the portions of the members when, during rotation two of the portions one on each member are in alignment with each other and with the second light beam, the light beams being diametrically opposite one another with respect to the axis of rotation of the first and second members, and each beam having a width parallel to the plane of rotation of the members which is greater than the spacing of corresponding points in adjacent portions on that member which has the larger spacing, first and second light-sensitive means positioned to receive light from the light beams through portions in alignment with the first and second light beams, respectively, and to provide two pulse trains, and means for indicating the sum of the repetition frequencies of the pulse trains.

Claim 15

A tachogenerator according to claim 12 including a plurality of optical systems each comprising two means for projecting a light beam through the portions of the members when, during rotation, two of the portions one on each member are in alignment with each other and with one of the light beams, each light beam having a width parallel to the plane of rotation of the members which is greater than the spacing of corresponding points in adjacent portions on that member which has the larger spacing, and two light-sensitive means one for each light beam and positioned to receive light through portions in alignment with that light beam the first and second members having a common axis of rotation, the opticaL system being evenly spaced round a circle co-axial with the common axis, and the light-sensitive means of the optical systems being coupled to the means for indicating the sum of the repetition frequencies of the pulse trains, or for indicating the magnitude of the samples of the said sum.