Measuring apparatus

Claim 2

Measuring apparatus responsive to the position of a first object movable relative to a second object including a code member secured to the second objeCt and carrying a sequence of binary digital elements which extends in the direction of relative movement of said second object with respect to said first object and forming a chain code and is such that any group of a predetermined number N of consecutive elements differs in pattern from any other group of N consecutive elements, and identifying means located to respond to said elements and operable at any relative position of the objects within the resolution of the patterns to derive a measurement signal which identifies that position in terms of a particular one of said groups said identifying means including a register, transfer means located to respond to said elements by transferring to the register the digital pattern of the particular group of elements which at any given moment represents the said relative position of the first object at that moment, a code generator operable on pulse energization to generate successive ones of said group patterns, a pulse source connected to pulse-energize the code generator, comparison means interconnected with the register and the code generator so as to respond when their patterns are the same, and output means responsive to said source and the comparison means to derive the said measurement signal from the number of pulses applied to energize the code generator to cause the comparison means to respond when their patterns are the same.

Claim 3

Apparatus as claimed in claim 1 wherein the output means includes a counter and connecting means for applying to said counter pulses from said source until the comparison means responds as aforesaid, whereby the number held in the counter at any given moment represents the said relative position at that moment.

Claim 4

Apparatus as claimed in claim 1 where the code member is an optical grating ruled to represent said patterns and wherein the transfer means includes scanning means movable with the second object and operable at any relative position of the objects within the resolution of the patterns to irradiate digit-by-digit in turn a portion of the code member including the particular one of said groups which represents that position, a photoelectric device disposed to be sequentially irradiated by said portion as scanned and represent it by a series train of at least said number of digital signals, and group-selecting arrangements for applying to the register the N digital signals representing said particular group.

Claim 5

Apparatus as claimed in claim 4 including a further optical grating to enable said scanning means to derive a pulse for strobing the digital signals derived from the code member so as to pass to the register only an approximately central part of each such digital signal.

Claim 6

Apparatus as claimed in claim 3 wherein to supplement the said measurement signal there is provided control and reference optical gratings secured to the first and to the second object respectively, further scanning means movable with the second object and operable in synchronism with the first-mentioned scanning means to irradiate those gratings so as to set up similar cyclic control and reference patterns of wavelength proportional to the pitch of the code elements and of relative phase dependent on the relative position of the objects, control and reference photoelectric devices disposed so as to be irradiated by light from those patterns, means responsive to the relative phase of the control and reference signals from those devices to indicate the relative position of the objects within the space between adjacent ones of said digital elements, and means for causing the control signal to strobe the digital signals derived from the code member so as to pass to the register stage only an approximately central part of each such digital signal.

Claim 7

Apparatus as claimed in claim 1 wherein the transfer means includes a set of N pickoff devices disposed to respond to the N digital elements of the particular patteRn which represents the said relative position of the first object, and connection means for applying the outputs from said N pickoff devices to the register.

Claim 8

Apparatus as claimed in claim 6 which includes a further set of N pickoff devices disposed to respond to said elements but displaced by half a pitch of said elements from the set first mentioned, a switching stage for selectively connecting said sets to the register, and means for controlling the switching stage so as to connect to the register at any given moment the particular one of said sets that is the more centrally aligned on said elements at that moment.

Claim 9

Apparatus as claimed in claim 6 where the code member is an optical grating, wherein the pickoff devices are photoelectric devices and means are provided for irradiating the code member to enable the devices to respond to said elements.

Claim 10

Apparatus as claimed in claim 7 wherein to supplement the said measurement signal there is provided means for providing control and reference cyclic signals of wavelength proportional to the pitch of the code elements and of relative phase dependent on the relative position of the objects, means responsive to the relative phase of said cyclic signals to indicate the relative position of the objects within the space between adjacent ones of said elements, and means for deriving from those signals at least one signal to control the timing of the said identifying means.

Claim 11

Apparatus as claimed in claim 1 wherein the register and the code generator form a combined unit, and further including a logic network interconnected with the unit to condition it to function either as a shift register or as a code generator. means for actuating the logic network after the response of said transfer means to convert the unit from a register to a code generator whilst retaining the registered code pattern, said comparison means being interconnected with the unit to compare the condition of the unit with a datum condition thereof and respond as aforesaid on receipt by the unit of sufficient of said pulses to restore the generator to that datum condition, and means for actuating the logic network to restore the unit to function as a register before the next response of the transfer means.

Claim 12

Measuring apparatus responsive to the position of first object movable relative to a second object including a code member secured to the second object and carrying a sequence of binary digital elements which extends in the direction of relative movement of said second object with respect to said first object forming a chain code and is such that any group of a predetermined number N of consecutive elements differs in pattern from any other group of N consecutive elements, and identifying means including a combined shift register and code generator unit, a logic network interconnected with the unit to condition it to function either as a shift register or a code generator, transfer means located to respond to said elements by transferring to the unit when conditioned as a shift register the digital pattern of the particular group of N elements which at any given moment represents the said relative position of the first object at that moment, means for actuating the logic network after the response of said transfer means to convert the unit from its register condition to its code generator condition whilst retaining the registered code pattern, a source connected to supply pulses to step the unit when in its code generator condition so as to restore the patterns to a datum pattern, output means responsive to said source to derive a measurement signal which represents the relative position of the first object by the number of pulses required to step the code generator from the registered pattern to the datum pattern, and means for actuating the logic network to restore the unit to its register condition before the next response of the transfer means.

Claim 13

Measuring apparatus responsive to the position of first object movable relative to a second object including a code member secured to the second object and carrying a sequence of binary digital elements which extends in the direction of relative movement of said second object with respect to said first object forming a chain code and is such that any group of a predetermined number N of consecutive elements differs in pattern from any other group of N consecutive elements, and identifying means including a combined shift register and code generator unit, a logic network interconnected with the unit to condition it to function either as a shift register or a code generator, transfer means located to respond to said elements by transferring to the unit when conditioned as a shift register the digital pattern of the particular group of N elements which at any given moment represents the said relative position of the first object at that moment, means for actuating the logic network after the response of said transfer means to convert the unit from its register condition to its code generator condition whilst retaining the registered code pattern, a source connected to supply pulses to step the unit when in its code generator condition so as to restore the patterns to a datum pattern, output means responsive to said source to derive a measurement signal which represents the relative position of the first object by the number of pulses required to step the code generator from the registered pattern to the datum pattern, and means for actuating the logic network to restore the unit to its register condition before the next response of the transfer means.