Bar code reader and method of measuring bar codes.

Claim 2

A bar code measuring apparatus (10) having a first photodetector (44) receiving reflected light from a first point as the first photodetector is passed over bars and spaces, for sensing bars and spaces, means (58, 60) for producing first digital signals representative of the time of passing over each bar and each space; and digital signal storage means for storing the first digital signals; characterised by a second photodetector (48) spaced from the first photodetector (44) and receiving reflected light from a second point spaced from the first point, means (68, 70) for producing second digital signals representative of the time of passing of the second photodetector (48) over each bar and space, the second digital signals being also stored in the storage means; and digital processing means (76) for comparing the first digital signals with the second digital signals and for determining therefrom an absolute measurement of the width of each bar and/or space.

Claim 3

A bar code measuring apparatus (10) as claimed in Claim 1 in which the means for producing the digital signals includes a constant-frequency pulse generator (110), and counting means (116) connected to the constant-frequency pulse generator, the said producing means being arranged to produce the first and second digital signals by counting pulses between variations in output signals produced by the photodetectors (44, 48).

Claim 6

A method as claimed in Claim 3 where, in determining the absolute width, the velocity of the first and second photodetectors (44, 48) in passing over each bar and each space is determined by measuring the times at which they pass over a leading edge and/or a trailing edge of each bar and each space, and the distance between the leading and the trailing edges is determined from the said velocity and the time of passing of the photodetectors over each edge.

Claim 7

A method as claimed in Claim 4 in which the velocity determined is the average velocity in passing over each bar and each space.

Claim 8

A method as claimed in Claim 3 in which each bar and each space comprises a leading edge detected first by the photodetectors (44, 48) and a trailing edge detected after the first detection, and in producing the said digital signals an output signal is produced by each photodetector as it passes over each leading edge and each successive trailing edge.

Claim 9

A method as claimed in Claim 6 in which the output signals representative of the first photodetector (44) and of the second photodetector (48) passings over a leading edge are stored in a digital memory against clocked times and a velocity of the photodetectors passing over the leading edge is determined therefrom, and the signals representative of the first photodetector (44) and the second photodetector (48) passings over the succeeding trailing edge are stored against clocked times and a velocity of the photodetectors passing over the trailing edge is determined therefrom.

Claim 10

A method as claimed in Claim 7 in which the velocities of the photodetectors (44, 48) passings over a bar's or a space's leading edge and over its succeeding trailing edge are averaged, and the average velocity is used in determining the absolute width of the bar or the space.

Claim 11

A spatial distance measuring apparatus characterised by: a) a constant frequency pulse generator (110); b) digital signal processing means (76) connected to receive pulse signals from the generator, for processing digital information including the said pulses in accordance with a predetermined sequence of processing steps; c) digital storage means connected to the digital signal processing means (76) for providing stored digital signals to the processing means when accessed in accordance with the said predetermined sequence of processing steps; d) first photodetector means having a photodetector (44) capable of sensing light reflected from a first point and connected to the digital storage means, for producing and storing in the storage means first digital signals representative of the amount of light sensed at the first point; e) second photodetector means having a photodetector (48) capable of sensing light reflected from a second point spaced a fixed distance from the first point, the second photodetector means being connected to the digital storage means, for producing and storing in the storage means second digital signals representative of the amount of light sensed at the second point.

Claim 12

A spatial distance measuring apparatus characterised by: a) a constant frequency pulse generator (110); b) digital signal processing means (76) connected to receive pulse signals from the generator, for processing digital information including the said pulses in accordance with a predetermined sequence of processing steps; c) digital storage means connected to the digital signal processing means (76) for providing stored digital signals to the processing means when accessed in accordance with the said predetermined sequence of processing steps; d) first photodetector means having a photodetector (44) capable of sensing light reflected from a first point and connected to the digital storage means, for producing and storing in the storage means first digital signals representative of the amount of light sensed at the first point; e) second photodetector means having a photodetector (48) capable of sensing light reflected from a second point spaced a fixed distance from the first point, the second photodetector means being connected to the digital storage means, for producing and storing in the storage means second digital signals representative of the amount of light sensed at the second point.

Claim 13

A spatial distance measuring apparatus as claimed in Claim 9 in which the digital processing means (76) further includes means for comparing the first and the second digital signals and for determining a velocity therefrom.

Claim 14

A spatial distance measuring apparatus as claimed in Claim 9 adapted for measuring the spatial distance of a marking having a differing reflectivity in relation to areas therearound, the marking being at least partially bounded by a leading edge and trailing edge, and in which each of the photodetector means includes means for producing corresponding digital signals representative of a change in reflectivity at the leading edge and at the trailing edge.

Claim 15

A spatial distance measuring apparatus as claimed in Claim 11 in which the digital processing means (76) includes means for determining a first velocity at which the first and said second photodetector means sensed the leading edge, and for determining a second velocity at which said first and said second photodetector means sensed the trailing edge, and for determining the average of the first and second velocities.

Claim 16

A spatial distance measuring apparatus as claimed in Claim 12 in which the digital processing means includes means for determining the spatial distance between the leading and the trailing edges on the basis of the average of the first and second velocities.