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MULTI-MODE ENCODER OUTPUT
CROSS-REFERENCE TO RELATED PATENT
The present application is related to co-pending U.S. patent application Ser. No. 11/490,577 filed on Jul. 21, 2006 by David A. Rehmann and David Kurt Klaffenbach and entitled ENCODER, the full disclosure of which is hereby 10 incorporated by reference.
Encoders are sometimes used to sense movement of an 15 object. Such encoders may be subject to errors such as duty cycle errors and channel phase errors.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a control system according to an example embodiment.
FIG. 2 is a flow diagram of an example method for the control system of FIG. 1 according to an example embodiment. 25
FIG. 3 is a diagram illustrating application of velocity criteria by an encoder output generator of the control system of FIG. 1 according to an example embodiment.
FIG. 4 is a block diagram schematically illustrating another embodiment of the encoder output generator of the 30 control system of FIG. 1 according to an example embodiment.
FIG. 5 is a state diagram of an encoder state machine of the encoder output generator of Figure numeral for according to an example embodiment. 35
FIG. 6 is a schematic illustration of an imaging apparatus including the output generators of FIG. 1 according to an example embodiment.
FIG. 7 is a flow diagram illustrating a method of an output averager of the imaging apparatus of FIG. 6 according to an 40 example embodiment.
FIG. 8 is a schematic illustration of another embodiment of an imaging apparatus including the output generators of FIG. 1 according to an example embodiment.
DETAILED DESCRIPTION OF THE EXAMPLE
FIG. 1 schematically illustrates control system 20 according to one example embodiment. Control system 20 pro- 50 vides closed loop control over the positioning of a sensed object 22. As will be described hereafter, control system 20 utilizes an encoder system 28 that operates in multiple modes to provide more accurate control over positioning of object 22. Control system 20 includes object 22, actuator 24, 55 controller 26 and encoder system 28.
Object 22 comprises any object, such as a mechanical component or the like, over which positional control is desired. In one embodiment, object 22 may be an object which is to be rotated in a controlled manner about an axis. 60 Examples of such objects include, but are not limited to, drums, rollers, wheels and the like. For example, in one embodiment object 22 may comprise a drum carrying printing material to be deposited upon a print medium or a drum caring a medium onto which printed material is to be 65 deposited. In other embodiments, object 22 may be an object which is to linearly or arcuately translate. For example, in
one embodiment, object 22 may comprise one or more print heads which are carried by a carriage that linearly translates as it is scanned across a medium. In still other embodiments, object 22 may have other configurations and other uses.
Actuator 24 comprises a mechanism configured to move object 22. In one embodiment, actuator 24 may be configured to rotate object 22 about one or more axes. In yet another embodiment, actuator 24 may comprise a mechanism configured to linearly or arcuately translate object 22. In one embodiment, actuator 24 may comprise a motor and a transmission for delivering torque from the motor to the object so as to rotate the object or so as to convert the torque so as to linearly or arcuately translate or move the object. Examples of such a transition may include one or more gear trains, chain and sprocket arrangements, belt and pulley arrangements, cam and cam follower arrangements and the like. In yet other embodiments, actuator 24 may comprise a hydraulic or pneumatic cylinder-piston assembly or an electric solenoid, wherein linear motion from such is transmitted by a transmission to object 22 to rotate or translate object 22. Actuator 24 may have any of a variety of different configurations for generating and transmitting motion to object 22.
Controller 26 comprises one or more processing units configure to generate control signals for directing operation of actuator 24 so as to move object 22. For purposes of this application, the term "processing unit" shall mean a presently developed or future developed processing unit that executes sequences of instructions contained in a memory. Execution of the sequences of instructions causes the processing unit to perform steps such as generating control signals. The instructions may be loaded in a random access memory (RAM) for execution by the processing unit from a read only memory (ROM), a mass storage device, or some other persistent storage. In other embodiments, hard wired circuitry may be used in place of or in combination with software instructions to implement the functions described. For example, controller 26 may be embodied as part of one or more application-specific integrated circuits (ASICs). Unless otherwise specifically noted, the controller is not limited to any specific combination of hardware circuitry and software, nor to any particular source for the instructions executed by the processing unit. Controller 26 generates such control signals which ultimately control the positioning of object 22 as well as potentially its velocity and acceleration between different positions based at least partially upon signals from encoder system 28.
Encoder system 28 comprises a system configured to detect movement of object 22 and to produce output signals representative of such movement. As will be described, encoder system 28 operates in multiple modes to increase its accuracy and reliability. In particular, encoder system 28 switches between different modes to output signals even when object 22 is undergoing slow or erratic movement and to also output more accurate signals when object 22 is moving at generally higher and more uniform velocities. As a result, the positioning of object 22 by actuator 24 based upon control signals from controller 26 is also more accurate and reliable.
Encoder system 28 includes encoder track 30, sensor 32 and output generator 34. encoder track 30 comprises a series of notches, slits, markings or other structures or surface treatments (hereafter referred to as marks 35) having edges 36 equidistantly spaced from one another by predetermined increments and configured to be sensed by sensor 32. In the example illustrated, marks 35 comprise a multitude of slits or transparent lines configured to permit passage of light,
wherein portions of track 30 between marks 35 in or up the transmission of light. In other embodiments, track 30 may have other configurations.
Sensor 32 comprises a device configured to sense relative movement between track 30 and sensor 32. In particular, 5 sensor 32 is configured to generate a signal as an edge 36 and sensor 32 move relative to one another. In the particular example illustrated, sensor 32 comprises an optical sensor having a light emitter element in a light sensing element on opposite sides of track 30. As track and 30 is moved relative 10 to sensor 32 or as Sensor 32 is moved relative to track 30 (or both), the light from the emitter element being received by the sensing element is repeatedly interrupted by those portions of each order track 30 between marks 35, wherein sensor 32 generates pulses are signals based upon such 15 repeated interruptions.
As shown by FIG. 1, sensor 32 includes a first channel 40 and a second channel 42, wherein each of channels 40, 42 senses transitioning of edges 36. For example, Channel 40 senses both (1) positive, leading or rising edges and (2) 20 negative, trailing or falling edges 36 associated with each mark 35. Channel 42 also senses both positive, leading or rising edges and negative, trailing or falling edges 36 associated with each mark 35.
Channels 40, 42 are out of phase with respect to one 25 another. For example, in one embodiment, channel 40 and channel 42 are out of phase with one another by 90 degrees. As a result, sensor 32 may not only detect speed but may also detect direction. According to one embodiment, sensor 32 comprises a quadrature encoder, wherein channel 40 30 comprises channel A and wherein channel 42 comprises channel B. In other embodiments, other encoder track sensing devices may be employed.
In the particular example illustrated, as indicated by solid lines 45, encoder track 30 is physically coupled or connected 35 to object 22 so as to move with object 22. In such an embodiment, sensor 32 may be supporting the stationary manner with respect to encoder track 30 and object 22. In other embodiments, as indicated by broken lines 47, object 22 may alternatively be physically coupled and connected to 40 sensor 32. In such an embodiment from actuator 24 moves object 22 and sensor 32 relative to track 30. In such an embodiment, track 30 may be stationary. Although track 30 is illustrated as being linear, track 30 may alternatively be circumferential or arcuate such as when track 30 is provided 45 on an encoder disc or wheel.
Output generator 34 comprises a device configured to receive sensed edge signals 44, 46 from both channels 40, 42 of sensor 32 and to operate in one of two modes: (1) an interpolation or synthesizing mode 50 or (2) a pass-through 50 mode 52. In the interpolation mode, output generator 34 produces or synthesizes output signals 56 using less than all of the sensed edge signals received from sensor 32. Output generator 34 synthesizes such output signals 56 by interpolation, using only a portion of the received sensed edge 55 signals for carrying out the interpolation. In the example illustrated, output generator 34 performs interpolation using a single type of edge from a single channel 40, 42 of sensor 32. The remaining sensed edges are not used in the interpolation. For example, in one embodiment, output generator 60 34 may interpolate using the sensed edge signals 44 from channel 40 that correspond to transitioning of leading edges 36. Sensed edge signals 44 which correspond to transitioning of trailing edges 36 are not used. The sensed edge signals 46 from channel 42 corresponding to either the leading edge 65 or the trailing edge are not used. In other embodiments, output generator 34 may alternatively perform such inter
polation using sensed edge signals 44 from channel 40 corresponding to the trailing edge, sensed edge signals from channel 42 corresponding to the leading edge or sensed edge signals and 46 from channel 42 corresponding to the trailing edge.
Because output generator 34 outputs signals 56 in the interpolation mode 50 using less than all of the received sensed edge signals from channels 40 and 42 of sensor 32, the output signals 56 may be more accurate. In particular, because output generator 34 outputs signals 56 based on sensed edge signals 44, 46 from a single channel 40, 42, output generator 34 reduces or eliminates channel phase errors. Channel phase errors may result from manufacturing variations or tolerances associated with the relative positioning of the sensing or detection elements of channels 40 and 42. For example, channels 40 and 42 may not be exactly 90 degrees out of phase with respect to one another due to manufacturing variations.
Because output generator 34 outputs signals 56 based upon sensed edge signals 44, 46 that correspond to movement or transitioning of a single type of edge, a leading edge or a trailing edge, output generator 34 reduces or eliminates duty cycle errors. Duty cycle errors may be the result of variations between spacing of marks 35. Duty cycle errors may also be the result of variations between the light emitting elements or variability over the life of such light emitting elements and the sensing thresholds of detecting elements.
Because output generator 34 synthesizes new replacement output signals 56 corresponding to the three sensed edge signals that were received, but which were discarded or not used, output generator 34 produces at least same number of output signals 56 as the number of sensed edge signals received from sensor 32. As a result, output generator 34 maintains the same level of resolution. In the example embodiment illustrated, output generator 34 synthesizes the replacement signals 56 using interpolation. In other embodiments, the replacement signals may be synthesized in other manners.
In the embodiment illustrated, output generator 34 interpolates by the same factor as the number of received sensed edge signals. In the example illustrated, output generator 34 receives four sensed edge signals—a leading edge and a trailing edge sensed edge signal from each of channels 40 and 42. As a result, output generator 34 interpolates with a factor of four. For example, in one embodiment, upon receiving a sensed edge signal from channel 40 corresponding to transitioning of a leading edge, output generator 34 determines an amount of time that has elapsed since previous receipt of a sensed edge signal from channel 40 also corresponding to transitioning of the leading edge. Output generator 34 divides this elapsed time value by the interpolation factor, four, to determine the interpolated time period. Thereafter, in addition to outputting a signal 56 corresponding to the sensed edge signal 44 from channel 40 corresponding to transitioning of the leading edge, output generator 34 also generates the next successive three interpolated output signals 56. This process is repeated upon receipt of the next sensed edge signal 44 corresponding to the transitioning of the leading edge and continues until output generator switches to pass-through mode 52.
In the pass-through mode, output generator 34 outputs signals 56 which correspond to each of the sensed edge signals 44 and 46 from both channels 40 and 42, respectively. In one embodiment, output generator 34 transmits the received sensed output signals and outputs such signals as output signals 56 without modifying such signals. In another