The present invention relates to an encoder and an optical identification system, and more specifically to an encoder to be mounted on a movable object to be measured without disassembling for measuring the mode of movement and an optical identification system suited for identifying the information carried on label media.
Various techniques have been proposed as an encoder to measure the movement mode of shaft rotation for, for example, a stepping motor and the like. A measurement of the rotation mode of the motor shaft can be made by directly coupling the encoder to the motor shaft. However, it is not easy to measure the rotation mode after assembling the motor to associated mechanical parts.
Examples of measuring the rotation mode of an assembled motor shaft are Illustrated in FIGS. 23 and 24. In FIG. 23, an encoder 104 is mounted onto a shaft 103 directly coupled to a rotary portion of a mechanical part 100 coupled to a shaft of a motor 102. In FIG. 24, the encoder 104 is coupled to a separate shaft 103A at the side of the motor 102 opposite to the mechanical part 100.
Illustrated in FIG. 25 is a typical construction of the encoder. In FIG. 25, a large number of apertures A are formed radially along the periphery of a rotary disc 110 directly coupled to the shaft 100. A light emitting diode 111 and a light receiving device 112 are disposed at both sides of the apertures A. The light beam from the light emitting diode 111 is received by the light receiving diode 112 through the apertures A of the rotary disc 110 and converted into an electrical signal to be applied to one input of a voltage comparator 113. The voltage comparator 113 compares the input signal with a threshold level supplied to the other input (not shown) to obtain a pulse signal. The pulse signal thus obtained is used to measure the rotation mode such as rotary angle, rotary direction, rotary speed. Illustrated in FIG. 26 are A phase, B phase and Z phase output pulses From the voltage comparator 113 in FIG. 25, where the A phase and B phase output pulses are derived from apertures slightly shifted in the rotary direction. The Z phase output pulse is derived from a reference aperture (not shown) at one location in the periphery. The phase relationship and period T of these pulses are used to obtain the rotary direction and rotary speed. In the drawing, CW means clockwise while CCW means counterclockwise.
In such conventional encoder, it is required to couple the encoder 104 to the shaft 103 of the mechanical part 100 to be measured as shown in FIG. 23. Such coupling requires a specially designed construction intended to couple the encoder, thereby resulting in increased cost. Accordingly, in a compact construction typical in 0A equipments and the like, it is required to couple the encoder for the purpose of performance inspection and the like. In the construction as illustrated in FIG. 24, it is required to provide the special shaft 103 for coupling the encoder to the motor, thereby increasing cost.
In other words, it was very difficult to mount an encoder to mechanical parts that are not intended to mount the encoder. This is a large obstacle in performing various tests of quantity production apparatus.
On the other hand, a bar code or label media comprising alternating patterns of regular block and white stripes on a tape-shaped sheet has been used very extensively. Such bar code label media is advantageous in that the label media can be made by simple printing technology and that a large number of code information can be indicated by choosing the number and the arrangement of the black and white patterns. Also widely used is an optical identification system to identify the bar code information by directing and scanning a light (laser beam) onto the bar code label placed on various goods and by detecting the reflected light from the surface of the bar code label with an optical detector. The reflected light is modulated responsive to the bar code.
The conventional bar code mostly comprises alternating black and white stripes over a certain length. However, such conventional bar code label media has the following shortcomings.
For effective reception of the reflected light from the label, the laser beam must be directed normal to the label media to be detected by an optical detector positioned also in the normal line. However, it is usually very difficult to direct the laser beam normal to the label media placed on goods which are held by an operator. Accordingly, the angle of the incident laser beam onto the bar code surface is not normally at a right angle to the surface and may vary over a wide range. As a result, the reflected laser beam tends to vary over a wide angle, thereby requiring the design of the optical detector to have a large light receiving area so as to respond to such reflected light. This results in complexity in optical detection and increased size and cost of the optical identification system.
It may be possible to locate the light source (light emitting diode) and the optical detector (light receiving diode) in a symmetrical angle with respect to the normal line to the object so that the reflected laser beam from the incident surface is collected at a relatively narrow area where the light receiving surface of the optical detector is placed. However, even in this case, the light receiving surface must be relatively large because of the same reason as the above. In addition, positioning the light emitting (or laser) diode and the optical detector with a predetermined distance therebetween is difficult to achieve in compact system designs and costly. These problems are common to optical identification systems for identifying bar codes on label media.