Method for detecting a position of an actuator
An encoding sequence is configured to detect the position and direction of motion of an actuator. The actuator includes at least two members where one of the members moves with respect to the other. Two sets of binary indicators are either affixed to or integrally assembled along one of the members. Each pair of indicators defines a position of the actuator and each binary indicator is configured to identify one of two states, such as a magnetic pole or a graphical mark where each state corresponds to a logical zero or a logical one. The indicators are arranged on the actuator such that at least one of the indicators transitions between one of the two states at each position along the actuator. At least one sensor is provided to detect the state of the binary indicators as the two members of the actuator move with respect to each other.
1. A method for detecting a position of an actuator, t actuator having a first member axially movable with respect to a second member, comprising the steps of:
axially spacing a first set of binary indicators located in a first plane along the first member of the actuator, wherein each binary indicator defines one bit within a word, the word has a predefined length, and each binary indicator defining a position of the first member with respect to the second member;
axially spacing a second set of binary indicators located in a second plane along the first member of the actuator, wherein the second plane is generally parallel to the first plane and each of the binary indicators in the second set corresponds to one of the binary indicators in the first set;
positioning at least one sensor at a location radially spaced from the first actuator, the sensor configured to generate a first signal corresponding to the change of state of the first set of binary indicators and to generate a second signal corresponding to the change of state of the second set of binary indicators;
moving the actuator a distance corresponding to the word length of each set of the binary indicators;
sensing the first and second sets of binary indicators with the at least one sensor while moving the actuator; and
determining the position of the actuator as a function of the first and second signals.
2. The method of step 1 wherein sensing the first and second sets of binary indicators further comprises the step of:
detecting a change of state in each of the first and second sets of binary indicators, wherein at least one of the first and second sets of binary indicators changes state at each position.
3. The method of claim 2 further comprising the step of determining a direction of motion of the actuator as a function of the first and second signals.
4. The method of claim 3 wherein:
the word length for each of the first set and second set of binary indicators is defined by a first start bit, a second start bit, and a plurality of data bits;
the first and second start bits of the first set of binary indicators are set equal to each other;
one of the first and second start bits of the second set of binary indicators is set to a logical one; and
the other of the first and second start bits of the second set of binary indicators is set to a logical zero.
5. The method of claim 3 wherein:
the word length for each of the first set and second set of binary indicators is defined by a first start bit and a plurality of data bits;
the start bit is set equal to the first data bit for the first set of binary indicators;
the remaining data bits for the first set of binary indicators alternate from the previous data bit; and
the start bit is set opposite to the first data bit for the second set of binary indicators.
6. The method of claim 3 wherein:
the word length for each of the first set and second set of binary indicators is defined by a first start bit, a second start bit, a third start bit, and a plurality of data bits;
each of the first, second, and third start bits of the first set of binary indicators is set equal to the preceding bit; and
each of the first, second, and third start bits of the second set of binary indicators is set opposite to the preceding bit.