1. Field of the Invention
The present invention relates to a detecting device for detecting a transfer object, such as a document sheet or recording paper, in a facsimile machine, a printer, a copying machine or an image scanner for example.
2. Description of the Related Art
In a facsimile machine for example, it is necessary to detect the movement or presence of a transfer object, such as a document sheet or a recording paper sheet, in a transfer path for controlling the operation of the facsimile machine. For this purpose, a detecting device is provided which comprises an actuator and a sensor.
More specifically, as shown in FIG. 8, a prior detecting device comprises an actuator 100 and a sensor 101. The actuator 100 includes a horizontal shaft 100a, a first arm 100b extending upwardly from the shaft 100a, and a second arm 100c extending downwardly from one end of the shaft 100a. The sensor 101 is mounted on a circuit board 102.
In the absence of a transfer object (not shown) in the transfer path, the first arm 100b of the actuator 100 projects into the transfer path. On the other hand, when a transfer object is present in the transfer path, the first arm 100b comes into engagement with the transfer object and is thereby pressed downwardly. In this way, the actuator 100 pivots up and down about the horizontal shaft 100a in response to the presence and absence of a transfer object.
The second arm 100c of the actuator 100 is bent to extend first obliquely and then substantially vertically. Since the second arm 100c is thus bent, the actual orientation of the second arm may be represented by an effective length line EL which passes through the center of the actuator shaft 100a and the lower end of the second arm 100c. In the absence of a transfer object in the transfer path, the angle .theta. between the effective length line EL of the second arm 100c and a vertical line VL passing through the center of the shaft 100a is less than 45.degree..
The lower end of the second arm 100c is provided with a reflector 103 which faces the sensor 101 when the second arm 100c is pivoted down due to the absence of a transfer object. Further, the reflector 103 has a rounded stopper projection 104 which comes into resting contact with the circuit board 102, thereby maintaining a predetermined clearance H.sub.1 between the reflector 103 and the circuit board 102.
The sensor 101 is a reflection type sensor which has a light emitting portion and a light receiving portion. When the actuator 100 is pivoted to bring the stopper projection 104 into contact with the circuit board 102, the light emitted from the light emitting portion of the sensor 101 is reflected on the reflector 103 for incidence into the light receiving portion of the sensor 101, so that the sensor 101 notifies the absence of a transfer object. On the other hand, when the second arm 100c of the actuator 100 is pivoted up due to the presence of a transfer object, the reflector 103 becomes far from the sensor 101 to come completely out of the light reflecting position (see the phantom line in the center of FIG. 8), so that the sensor 101 notifies the presence of a transfer object.
Normally, the circuit board 102 is mounted at a standard distance H.sub.0 from the actuator shaft 100a to make the reflector 103 substantially parallel to the upper surface of the sensor 101 in facing relation thereto (see the center representation in FIG. 8) when the stopper projection 104 of the reflector 104 comes into contact with the circuit board 102. However, it is possible, due to some production or assembly error, that the circuit board 102 may positionally deviate from the standard distance position H.sub.0 relative to the actuator shaft 100a. If the circuit board 102 is erroneously positioned at a distance (H.sub.0 -.DELTA.H) or (H.sub.0 .DELTA.H) from the actuator shaft 100a (see the left and right representations in FIG. 8), the orientation of the reflector 103 becomes improper relative to the upper surface of the sensor 101. As a result, the sensor 101 may fail to provide a reliable detection of a transfer object. Such a disadvantage will become particularly remarkable as the angle .theta. between the effective length line EL of the actuator second arm 100c and the vertical line VL is small.