Rotary encoders of optical or magnetic construction are used to measure or sense rotation, typically of a shaft or the like, by providing rotational-related data from which information, such as absolute or relative rotary position can be determined. Rotary encoders are very versatile and used in applications that frequently require controlling the motion of a rotating object, such as a shaft or the like. Other applications include: monitoring motor feedback, cut-to-length applications, filling applications, backstop applications, robotics, etc.
Optical rotary encoders typically use a circular disk that has sections coded, such as by being blacked out or otherwise marked, that turns with the object whose rotary movement is being measured. A sensor reads light reflected from the disk in determining whether there has been a change in rotary position of the disk.
While optical rotary encoders have enjoyed a great deal of commercial success, they nonetheless suffer from numerous drawbacks. They are undesirably complicated, sensitive to dust, oil and dirt, mechanically fragile, typically cannot be used in relatively high temperature environments, and are susceptible to shock and vibration.
Magnetic rotary encoders have a construction that overcomes most, if not nearly all, of these disadvantages. Many magnetic rotary encoders include relatively precise axial and radial positioning of an encoder shaft-mounted magnet used to excite Hall Effect sensors that define a sensor region of a magnetic rotary encoder chip.
In some applications, to determine an absolute position, a first magnetic rotary encoder chip (angle sensor) can be used to sense a current angle of the rotary system with respect to a first reference line, while a second magnetic rotary encoder chip (turn sensor) can be used to track a count of complete rotations or turns of the rotary system with respect to a second reference line. For example, as a rotary system rotates, the angle sensor can sense this condition accordingly and can determine a current angle of the system with respect to the first reference line. In addition, as the system rotates through a complete rotation in positive/clock-wise direction with respect to the second reference line, the turn sensor can sense this condition and increment a count by one. Conversely, as the system rotates back in a negative/counter-clock-wise direction past the second reference line, the turn sensor can sense this condition and decrement the count by one. The count from the turn sensor and the current angle from the angle sensor together can provide an absolute position when queried.
While precise alignment between the aforementioned reference lines of the sensors is ideal, in practical implementations, some error between the reference lines typically exists. As a result, it is oftentimes necessary for one of the sensor chips, or a microcontroller in the system, to synchronize the measurements between the sensor chips in order to determine a consistent absolute position. However, for one of the sensor chips to synchronize the measurements, it is often necessary for the other sensor chip to present sensed data in a predetermined way that would be recognized by the synchronizing sensor chip. This limits the possibility of sensor chips to ones that are strictly compatible in this regard, which might not include sensor chips providing the highest accuracy, lowest power consumption and/or lowest cost. Also, for the microcontroller to synchronize the measurements, it is often necessary to implement additional software for the microcontroller to execute. This can result in inefficient processing delays which may not be acceptable in the system.
What is therefore needed is a system for absolute position sensing which overcomes one or more of the aforementioned drawbacks.