JPH0197911A - Position detector for lens - Google Patents

Abstract

PURPOSE:To improve the detection precision, to reduce the space, and to surely detect the terminal by digitally detecting the terminal and analogically detecting the middle position. CONSTITUTION:When a lens barrel 1 is placed in the shortest focus position, a contact 9 short-circuits the circuit between conductor films 5 and 8 and the potential of the conductor film 8 is set to the turning-on state, and a position detecting circuit 11 discriminates this position. The contact 9 short-circuits the circuit between a resistance film 3 and a conductor film 6 according as the lens barrel 1 is moved toward the infinity focus position, and a voltage proportional to this short-circuit position is taken out to the conductor film 6 and is read as a digital signal by an A/D converter 12. When the lens barrel 1 reaches the infinity focus position finally, the contact 9 short-circuits the circuit between conductor films 4 and 7 to set the conductor film 7 to the turning-on state and this position is discriminated. Thus, the terminal is surely detected and the space is reduced and the resolution is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an autofocus camera, and more particularly to a position detection device for a power zoom lens.

-Background of the Invention- In an automatic focus camera, the position of a photographing lens is detected in order to adjust the focus of a lens system on a film surface in accordance with a distance measurement signal for a subject. Furthermore, a camera incorporating a zoom lens also requires zoom position detection.

For such lens position detection, as shown in Fig. 2,
An encoder pattern IA is formed on the outer peripheral surface of the lens barrel 1, and a multi-bit signal is obtained from the contact 2 based on the positional relationship between the pattern IA and the contact 2 when the lens barrel 1 is driven, and this signal is used to determine the lens position. Make information.

Problems to be Solved by the Invention - In conventional position detection devices, the moving distance from the shortest focus position of the lens to the afocal position is obtained as digital information with a bit pattern of the number necessary for the resolution. As the number of focal positions to be set increases, the number of bits of the pattern IA increases, and this poses a problem in that it is difficult to increase the number of bits due to restrictions on the pattern formation area, and it is also difficult to improve the resolution of the focal position. Furthermore, the number of contacts and the number of signal lines thereof will increase.

Regarding this point, it is conceivable to provide a sliding resistance (potentiometer) in the lens barrel 1 and detect the position in an analog manner, but in this detection method, an analog voltage and a reference position voltage (for example, a voltage corresponding to the shortest focus position) are used. Since the current position is determined by comparison with the current position, there is a problem that the error tends to be large. In particular, when detecting the position of a power zoom lens, it is necessary to detect the end position such as the shortest focus position, but when driving the lens, a relatively large current flows through the motor, making it easy for noise to be added to the voltage line of the potentiometer and the reference position voltage. Detection errors are more likely to occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a position detection device that can ensure end detection, has a small space, and has high resolution.

Means and operation for solving one problem - In order to achieve the above-mentioned object, the present invention provides a sliding resistance formed along the position detection direction of the lens barrel and a voltage applied thereto; A pair of sliding conductors formed at both ends of the resistor, and a contactor for contacting the sliding conductor and the sliding resistor by means of a lens barrel and detecting the electric potential at the contact position as the lens position, The terminal position is detected by the contact of the contact with the sliding conductor, and the intermediate position is detected by the voltage at the position where the contact comes into contact with the sliding resistance.

One Embodiment - FIG. 1 is a main part configuration diagram showing one embodiment of the present invention. A strip-shaped sliding resistance film 3 is formed on the outer circumferential surface of the lens barrel 1 along the position detection direction (indicated by arrow P) for detecting its movement, and a pair of chip conductor films 4.5 are formed at both ends of the sliding resistance film 3. It is formed. A strip-shaped conductive film 6 is formed in parallel to the resistive film 3.
A chip conductor film 7.8 is formed in parallel to chip conductor film 4.5.

A voltage VCC is applied to both ends of the resistive film 3, and the conductive film 4.
5 is set to a reference potential. Then, a resistive film 3 and a conductive film 4
．． A conductor film 6 and a contactor 9 having a gap extending over 7.8 are provided on an outer barrel 10 of the lens barrel, respectively. Further, the conductor films 6, 7, 8 are each drawn into the position detection circuit 11 side by lead wires. The position detection circuit 11 is a conductive film 6
The voltage of the conductive film 7.8 is converted into a digital signal by the A/D converter 12 and taken into the processor 13, and the voltage of the conductive film 7.8 is taken in as an on/off signal by the buffers 14 and 15, and position detection information is obtained from these signals.

In such a configuration, when the lens barrel 1 is at the shortest focus position, the contact 9 short-circuits the conductor film 5.8, the potential of the conductor 1Ii8 is turned on, and the position detection circuit 11 determines the position. . Then, as the lens barrel 1 moves toward the afocal position, the contactor 9 short-circuits the resistive film 3 and the conductive film 6, and a voltage proportional to this short-circuit position is taken out to the conductive film 6, and this voltage is The A/D converter 12 reads it as a digital signal. Finally, when the lens barrel 1 reaches the afocal position, the contactor 9 short-circuits the conductor films 4 and 7, and the conductor film 70 is turned on, thereby determining the position.

Therefore, the final position where the lens barrel 1 becomes the shortest focus position or the infinite focus position is detected digitally as an on/off signal, and the intermediate position is detected analogously. According to such a detection device, the positional resolution is high enough to be equivalent to that of an A/D converter, and the pattern formed on the lens barrel 1 requires only a small space.Furthermore, the termination is detected using an on/off signal. Therefore, end position detection has excellent noise resistance and is reliable.

Although the above-mentioned embodiment using a sliding resistor has been described, instead of the sliding resistor, a plurality of contact patterns arranged in the eight movement directions of the sliding conductor are arranged, and a potential difference is applied between these contact patterns. It may be.

Effects of the Invention As described above, according to the present invention, the end point is detected digitally and the intermediate position is detected in an analog manner, which has the effect of reducing the space while increasing the detection accuracy. The detection is ensured and an excellent effect is achieved in zoom lens position detection.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of main parts showing an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional device. 1... Lens barrel, 3... Resistive film, 4.5.6.7
．． 8... Conductor film, 9... Contactor, 11... Position detection circuit. Patent applicant Konishiroku Photo Industry Co., Ltd. Figure 2

Claims (1)

[Claims] 1) A sliding resistor formed along the position detection direction of the lens barrel and to which a voltage is applied, a pair of sliding conductors formed at both ends of this sliding resistor, and a sliding resistor formed along the position detection direction of the lens barrel, A lens position detection device comprising a sliding conductor and a contact element that contacts a sliding resistor and detects the electric potential at the contact position as the lens position.