The present invention relates to a mechanism in which a linear sensor is provided to detect a position of a movable member of a device such as a car stereo and a liquid display panel, and more particularly to a mechanism which converts the movement of the movable member into a linear movement of a slider in the linear sensor.
The car stereo and liquid crystal monitor are each provided with a linear sensor to detect a moving distance of a movable portion so that the movable portion may be controlled dependent on the detected distance. A magnetoresistance linear sensor or a electric resistance linear sensor is used as the linear sensor.
Referring to FIG. 8 showing a basic construction of a magnetoresistance linear sensor, the sensor has a flat and rectangular magnetic scale 30, a detector 31 disposed opposite the magnetic scale 30 and arranged to be relatively moved with respect thereto, and a signal processing circuit 32. The magnetic scale 30 comprises a base 33 and a magnetic medium 34 formed on the base 33. A plurality of magnetic scale plates 35 are mounted on the magnetic medium 34.
The detector 31 comprises a magnetoresistance element 36 and a holder 37 for supporting the magnetoresistance element 36. The magnetoresistance element 36 opposes the magnetic scale plates 35. When the detector 31 relatively moves along the scale plates 35, an output voltage generated by the magnetoresistance element 36 is applied to the signal processing circuit 32. The signal processing circuit 32, having a preamplifier 32A and a detecting circuit 32B, calculates the quantity of relative displacement of the detector 31.
FIG. 9 shows a basic construction of an electric resistance linear sensor. The linear sensor comprises a resistor 40 formed by printing substrate. The resistor 40 has a ground terminal 41 and a source terminal 42 at both the ends thereof. A movable contact 44 is adapted to contact and to slide across the resistor 40, thereby generating a voltage which varies in accordance with the position of the movable contact 44.
In order to detect a moving distance of a movable member with such a linear sensor, the sensor is further provided with a base member on which the magnetic scale 30 or the resistor 40 is mounted. The detector 31 or the movable contact 44 is mounted on a slider which is slides along the base member. The base member is attached to a fixed member of a device while the slider is attached to the movable member.
The linear sensor is disposed in a device in consideration to space efficiency therein. Hence, the slidable range, that is the stroke of the slider, or the moving direction thereof does not always coincide with the moving range or the direction of the movable member of the device. In addition, although the slider in the linear sensor is capable only of linear movement, some of the movable members such as a flap provided in a operational flap deck are angularly displaced. Hence the movable member is mounted on the slider of the linear sensor by way of a mechanism for converting the displacement of the movable member to a linear displacement within the slidable range of the slider.
FIGS. 5 to 7 show conventional mechanisms for detecting positions.
Referring to FIG. 5, a linear sensor 73 has a sensor base 73A and a slider 73B slidably mounted on the base 73A. The base 73A is mounted, by way of an attaching portion 73C, on a fixed member 71 of the device in which the sensor 73 is provided. The slider 73B is operatively connected to a movable member 72 of the device through an arm 50. More particularly, the arm 50 has an elongated hole 50B at a center thereof with which the slider 73B is engaged. An elongated hole 50A is formed at a base end of the arm 50 with which a pivot 51 projecting from the fixed member 71 is engaged, thereby pivotally mounting the arm 50 on the fixed member 71. The other end of the arm 50 is pivotally mounted on the movable member 72 by a screw 52. Thus, when the movable member 72 moves within a range R1, the slider 73B slides on the base 73A in a range R2, so that the linear displacement of the movable member 72 is detected as the linear displacement of the slider 73B. The ratio R1:R2 is determined in accordance with the position of the hole 50B for connecting the arm 50 with the slider 73B.
Referring to FIG. 6, a connecting plate 60 is attached to the movable member 72. The connecting plate 60 has a slide groove 60A inclined at a predetermined angle with respect to the moving direction of the movable member 72. The slider 73B is engaged with the groove 60A. The linear displacement of the movable member 72 in the range R1 is detected as the linear displacement of the slider 73B in the range R2 which extends in a direction perpendicular to the moving direction of the movable member 72. The ratio R1:R2 is determined in accordance with the angular position of the slide groove 60A.
In a conventional mechanism shown in FIG. 7, a slide plate 61 is further slidably mounted on the connecting plate 60. The slide plate 61 has a pair of parallel slide grooves 61A, each engaging a shaft 62 securely mounted on the fixed member 71 and extending in a direction perpendicular to the slide plate 61. The slider 73B of the linear sensor 73 is attached to the slide plate 61. Hence, the slide plate 61 slides in parallel to the sliding direction of the slider 73B. The linear movement of the movable member 72 is converted to linear movement of the slide plate 61 in the direction perpendicular to the moving direction of the movable member 72. The movement of the slider plate 61 causes the slider 73B to move on the base 73A.
However, there are problems in the above described conventional mechanisms. In the example shown in FIG. 5, the linear movement of the movable member 72 is converted to the angular displacement of the arm 50, and the angular displacement is further converted to the sliding movement of the slider 73B which is detected by the sensor. Thus the sliding distance of the slider 73B does not become proportional to the moving distance of the movable member 72, so that the sliding distance must be corrected by calculation. As a result, in the example of FIG. 5, the construction of the circuit becomes complicated.
Moreover, in the example of FIG. 5, the rotation of the arm 50 is transmitted to the slider 73B through the elongated hole 50B so that the slider 73B is exerted with force in the rotational direction of the arm 50.
In the example shown in FIG. 7, the slider 73B is applied with force in a direction inclined with respect to the inclination of the slide groove 60A. Hence in the examples of FIGS. 5 and 7, the slider 73B cannot smoothly slide on the base 73A. Furthermore, repeated operation causes mechanical damage to the linear sensor, so that the durability of the linear sensor is deteriorated.
In the examples shown in FIGS. 5 and 6, an extremely large space is required for the arm 50 to rotate or the connecting member 60 to slide so that the mechanism takes up a large space in the device. In particular, in the example of FIG. 7, in addition to the displacement of the connecting member 60, the slide plate 61 must be further moved so that the mechanism occupies a large portion of the space in the device. Namely, all of the above described examples are inferior in space efficiency. This is a serious problem in a device such as a stereo and decks having various moving devices and controllers densely disposed within.