EP0020199B1 — System for controlling the changing of the read s…

Claim 1

Independent Claim 414 words

System for changing the read face for an optical reader of data support (1) recorded on two faces (f 1 , f 2 ) the reading being carried out by using an optical device focalising a luminous beam on one of the previously selected faces; optical device comprising focalisation control circuits (CPO) comprising a feedback loop, to maintain constant the distance between the optical device and the surface of support (1) by a monitoring device dependant upon an electric signal, the reading of the recorded date supplying a high frequency (HF) modulated electric signal and detection means (2) receiving the high frequency (HF) modulated electric signal, the output of which supplies a detected signal (HFD) in the form of a binary signal assuming a first logic value when the amplitude of the high frequency signal is superior to a predetermined threshold (Ds) and a second logic value when the .amplitude of the high frequency signal is inferior to this threshold (Ds); system characterized in that it comprises: - first control means (CD,) to generate a binary signal for controlling the change of the read face (Cd), the two logic levels of which represent the two faces to be read (f 1 , f 2 ); -second control means (CD 2 ) combining the detected signal (HFD) and the binary signal for controlling the change of read face (Cd) in order to create a binary signal for the opening/closing of the feedback loop (OB), assuming a first logic level controlling the opening of the feedback loop, after reception of a transition of the control signal for changing the read face, and a second logic level controlling again the closing of the feedback loop after reception of a transition of the detected signal (HED) from the second to the first logic value; - and a control impulse generator for face change (GE) connected to the outputs of the first and second control means supplying to the focalisation control circuit (CPO) a control impulse for face change (15) synchronized with the transitions of the opening/closing signal of the feedback loop (OB); the polarity of the control impulse being such that it communicates alternately with the focalisation optical device (L) an accelerated movement towards the face previously selected at the moment of transition of second or first logic level of the opening/closing signal (OB) of the feedback loop and a deceleration at the moment of return to the second logic level allowing the focalisation on the selected face.

Claim 2

Dependent Claim 414 words

System for changing the read face for an optical reader of data support (1) recorded on two faces (f 1 , f 2 ) the reading being carried out by using an optical device focalising a luminous beam on one of the previously selected faces; optical device comprising focalisation control circuits (CPO) comprising a feedback loop, to maintain constant the distance between the optical device and the surface of support (1) by a monitoring device dependant upon an electric signal, the reading of the recorded date supplying a high frequency (HF) modulated electric signal and detection means (2) receiving the high frequency (HF) modulated electric signal, the output of which supplies a detected signal (HFD) in the form of a binary signal assuming a first logic value when the amplitude of the high frequency signal is superior to a predetermined threshold (Ds) and a second logic value when the .amplitude of the high frequency signal is inferior to this threshold (Ds); system characterized in that it comprises: - first control means (CD,) to generate a binary signal for controlling the change of the read face (Cd), the two logic levels of which represent the two faces to be read (f 1 , f 2 ); -second control means (CD 2 ) combining the detected signal (HFD) and the binary signal for controlling the change of read face (Cd) in order to create a binary signal for the opening/closing of the feedback loop (OB), assuming a first logic level controlling the opening of the feedback loop, after reception of a transition of the control signal for changing the read face, and a second logic level controlling again the closing of the feedback loop after reception of a transition of the detected signal (HED) from the second to the first logic value; - and a control impulse generator for face change (GE) connected to the outputs of the first and second control means supplying to the focalisation control circuit (CPO) a control impulse for face change (15) synchronized with the transitions of the opening/closing signal of the feedback loop (OB); the polarity of the control impulse being such that it communicates alternately with the focalisation optical device (L) an accelerated movement towards the face previously selected at the moment of transition of second or first logic level of the opening/closing signal (OB) of the feedback loop and a deceleration at the moment of return to the second logic level allowing the focalisation on the selected face.

Claim 3

Dependent Claim 92 words

System according to claim 1, characterized in that the second control means (CD 2 ) comprise, furthermore, a control device of the read face (DSU) receiving at regular paces, synchronized with the reading of the data recorded on support (1), a state signal (42) able to assume two distinct values, each representing one of the two faces of the recording support; the control device comprising permanent comparison means (8) of this signal (42) with the control signal for changing the read face (Cd), the output of which is transmitted to memorising means.

Claim 4

Dependent Claim 97 words

System according to claim 2, characterized in that the memorising means are constituted by a shifting memory (3) comprising several cells registering in the form of binary- coded impulses a predetermined number N of successive comparison results and by combining means (4) supplying an output impulse when N successive comparison results are negative and in that this output impulse is transmitted, via temporisation means (5, 6) to, on the one hand, a reinitialisation input (RAZ) of the shifting memory (3) and, on the other hand, to commutation means (7) comprised in second control means (CD 2 ).

Claim 5

Dependent Claim 15 words

System according to claim 3, characterized in that N is selected as equal to 8.

Claim 6

Dependent Claim 76 words

System according to any one of claims 2 to 4, characterized in that comparison means (8) are constituted by a first EXCLUSIVE-OR logic circuit, the memory with an eight-stage shift register (3), combination means (4) by a NAND logic circuit having eight inputs and temporisation means by two monostable muli- vibrators (5, 6) connected in series, the output of the second multivibrator (6) being connected to a return to zero input of the shift register (3).

Claim 7

Dependent Claim 132 words

System according to claims 1 and 5, characterized in that the first control means are constituted by a two-position commutator (D1), selecting by choice one of binary logic values "1" or "0", second commutation means (7) of second control means (CD 2 ) are constituted by a RS type flip-flop switch receiving on its entry S the output of the first monostable switch and on its input R, via a logic inverter circuit, the high frequency signal (FD); and in that the control impulse generator is constituted by a second logic EXCLUSIVE-OR circuit (9) receiving on a first input the true output of the RS type switch and on a second input the output of the two position commutator a resistance-capacitance circuit differentiating the output signal from the EXCLUSIVE-OR second logic circuit.

Claim 8

Dependent Claim 91 words

System according to claims 5 and 6, characterized in that the first monostable switch (5), delivers a temporisation impulse maintaining the RS-type flip-flop switch in a first state during a period longer than the time necessary for the decrease of the high-frequency signal modulated below the predetermined threshold and in that the second monostable switch delivers a temporisation impulse prohibiting the production of an impulse at the output of the NAND logic circuit during a period longer than the time necessary for the focalisation control circuits to change the read face.

System for controlling the changing of the read side for the optical reader of an information carrier

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