Abstract:
A double-bearing position encoder has an axle stabilized within a housing via two bearings disposed on opposite walls of the housing. The axle is in communications with a rotating cam. The cam actuates a pulser so as to generate an active pulse at a tissue site for analysis by an optical sensor. The axle rotates a slotted encoder wheel or a reflective encoder cylinder disposed within the housing so as to accurately determine the axle position and, hence, the active pulse frequency and phase.

Description:
PRIORITY CLAIM AND REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/847,307, filed Jul. 17, 2013 titled Double-Bearing Position Encoder, which is hereby incorporated in its entirety by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Noninvasive physiological monitoring systems for measuring constituents of circulating blood have advanced from basic pulse oximeters to monitors capable of measuring abnormal and total hemoglobin among other parameters. A basic pulse oximeter capable of measuring blood oxygen saturation typically includes an optical sensor, a monitor for processing sensor signals and displaying results and a cable electrically interconnecting the sensor and the monitor. A pulse oximetry sensor typically has a red wavelength light emitting diode (LED), an infrared (IR) wavelength LED and a photodiode detector. The LEDs and detector are attached to a patient tissue site, such as a finger. The cable transmits drive signals from the monitor to the LEDs, and the LEDs respond to the drive signals to transmit light into the tissue site. The detector generates a photoplethysmograph signal responsive to the emitted light after attenuation by pulsatile blood flow within the tissue site. The cable transmits the detector signal to the monitor, which processes the signal to provide a numerical readout of oxygen saturation (SpO 2 ) and pulse rate, along with an audible pulse indication of the person&#39;s pulse. The photoplethysmograph waveform may also be displayed. 
         [0003]    Conventional pulse oximetry assumes that arterial blood is the only pulsatile blood flow in the measurement site. During patient motion, venous blood also moves, which causes errors in conventional pulse oximetry. Advanced pulse oximetry processes the venous blood signal so as to report true arterial oxygen saturation and pulse rate under conditions of patient movement. Advanced pulse oximetry also functions under conditions of low perfusion (small signal amplitude), intense ambient light (artificial or sunlight) and electrosurgical instrument interference, which are scenarios where conventional pulse oximetry tends to fail. 
         [0004]    Advanced pulse oximetry is described in at least U.S. Pat. Nos. 6,770,028; 6,658,276; 6,157,850; 6,002,952; 5,769,785 and 5,758,644, which are assigned to Masimo Corporation (“Masimo”) of Irvine, Calif. and are incorporated in their entireties by reference herein. Corresponding low noise optical sensors are disclosed in at least U.S. Pat. Nos. 6,985,764; 6,813,511; 6,792,300; 6,256,523; 6,088,607; 5,782,757 and 5,638,818, which are also assigned to Masimo and are also incorporated in their entireties by reference herein. Advanced pulse oximetry systems including Masimo SET® low noise optical sensors and read through motion pulse oximetry monitors for measuring SpO 2 , pulse rate (PR) and perfusion index (PI) are available from Masimo. Optical sensors include any of Masimo LNOP®, LNCS®, SofTouch™ and Blue™ adhesive or reusable sensors. Pulse oximetry monitors include any of Masimo Rad-8®, Rad-5®, Rad®-5v or SatShare® monitors. 
         [0005]    Advanced blood parameter measurement systems are described in at least U.S. Pat. No. 7,647,083, filed Mar. 1, 2006, titled  Multiple Wavelength Sensor Equalization ; U.S. Pat. No. 7,729,733, filed Mar. 1, 2006, titled  Configurable Physiological Measurement System ; U.S. Pat. Pub. No. 2006/0211925, filed Mar. 1, 2006, titled  Physiological Parameter Confidence Measure  and U.S. Pat. Pub. No. 2006/0238358, filed Mar. 1, 2006, titled  Noninvasive Multi-Parameter Patient Monitor , all assigned to Cercacor Laboratories, Inc., Irvine, Calif. (“Cercacor”) and all incorporated in their entireties by reference herein. An advanced parameter measurement system that includes acoustic monitoring is described in U.S. Pat. Pub. No. 2010/0274099, filed Dec. 21, 2009, titled  Acoustic Sensor Assembly , assigned to Masimo and incorporated in its entirety by reference herein. 
         [0006]    Advanced blood parameter measurement systems include Masimo Rainbow® SET, which provides measurements in addition to SpO 2 , such as total hemoglobin (SpHb™), oxygen content (SpOC™), methemoglobin (SpMet®), carboxyhemoglobin (SpCO®) and PVI®. Advanced blood parameter sensors include Masimo Rainbow® adhesive, ReSposable™ and reusable sensors. Advanced blood parameter monitors include Masimo Radical-7™, Rad-87™ and Rad-57™ monitors, all available from Masimo. Advanced parameter measurement systems may also include acoustic monitoring such as acoustic respiration rate (RRa™) using a Rainbow Acoustic Sensor™ and Rad-87™ monitor, available from Masimo. Such advanced pulse oximeters, low noise sensors and advanced parameter systems have gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care and neonatal units, general wards, home care, physical training, and virtually all types of monitoring scenarios. 
         [0007]      FIG. 1  illustrates an active pulse generator  100  that installs within a reusable optical sensor for precisely pulsing a tissue site, such a fingertip. The active pulse generator  100  has a motor  110 , a cam  120 , a housing  130 , a pulser  140  and an optical encoder  200 . The cam  120  and pulser  140  are located within the housing  130 . A shaft  160  couples the motor  110  to the cam  120  so as to linearly-actuate the pulser  140  upon application of electric current to the motor  110 . The encoder  200  extends into the housing  130  so as to mechanically couple to the cam  120 . The encoder  200  measures the rotation of the cam  120  and hence the position of the pulser  140 . Based upon encoder feedback, the pulser  140  frequency and phase, and hence that of an active pulse, can be accurately measured and controlled. An active pulse reusable optical sensor is described in U.S. patent application Ser. No. 13/473,477, titled  Personal Health Device , filed May 16, 2012 and assigned to Cercacor is hereby incorporated in its entirety by reference herein. 
         [0008]      FIG. 2  further illustrates the encoder  200 , which has a housing  210 , a single-bearing  220  that mounts an encoder axle  230  to an encoder wheel  240  and an optics assembly that senses reflective position tracks and an index track on the encoder wheel  240  so as to generate a two-channel quadrature square wave output indicative of the axle  230  position. 
       SUMMARY OF THE INVENTION 
       [0009]    A single-bearing encoder wheel mount, as described with respect to  FIG. 2 , above, has insufficient mechanical stability to provide optimum accuracy in measuring and controlling the phase and frequency of an optical sensor active pulse. Double-bearing position encoder embodiments advantageously improve encoder wheel stability so as to improve active pulse accuracy and also solve encoder wheel/optical reader configuration issues created by the necessary location of the stabilizing second bearing. 
         [0010]    One aspect of a double-bearing position encoder is a housing, a pair of bearings disposed within opposite facing walls of the housing and an axle disposed within the housing and supported by the bearings. The axle is in mechanical communications with a pulser. An encoder wheel having wheel slots is fixedly attached to the axle. An LED is disposed within the housing so as to illuminate the encoder wheel. A detector is responsive to the LED illumination after optical interaction with the wheel slots as the axle rotates the wheel so as to indicate the wheel position. 
         [0011]    In an embodiment, the axle is stabilized within a housing via bearings disposed on opposite walls of the housing. The axle is in communications with a rotating cam that actuates a pulser so as to generate an active pulse at a tissue site for analysis by an optical sensor. The axle rotates a slotted encoder wheel or a reflective encoder cylinder so as to accurately determine the axle position and, hence, the active pulse frequency and phase. 
         [0012]    In various embodiment, the encoder comprisies an encoder mask having mask slots disposed over an edge and along both sides of the encoder wheel so that the LED illumination passes through the mask slots and the wheel slots before reaching the detector. The encoder mask is folded so that LED light is reflected off of the mask a first time before illuminating the encoder wheel and second time before reaching the detector. Alternatively, the encoder mask is folded so that LED light is not reflected off of the mask before illuminating the encoder wheel and before reaching the detector. 
         [0013]    Another aspect of a double-bearing position encoder is a rotatable axle. An encoder wheel is rotatably mounted on the double-bearing-mounted axle. An encoder mask is folded proximate an outer edge of the encoder wheel. Wheel slots are disposed around the encoder wheel proximate the outer edge. Mask slots are disposed through the encoder mask, and an emitter and a detector are disposed proximate to and on either side of the encoder wheel so that light intermittently passes through the encoder wheel via the wheel slots and the mask slots. 
         [0014]    In various embodiments, light is reflected from the emitter off of the mask at least once before it reaches the detector. Light is reflected from the emitter off of the mask twice before it reaches the detector. The emitter directly illuminates the detector without reflection off the mask. 
         [0015]    A further aspect of a double-bearing position encoder is a double bearing means of stabilizing a rotatable axle within an encoder housing. An encoder wheel means fixedly mounted to the axle so as to rotate as the axle rotates. An illumination and detection means of intermittently passing light through the encoder wheel means as it rotates, and a folded and slotted mask means of precisely passing light through encoder wheel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a perspective illustration of an optical sensor active pulse generator including a single-bearing position encoder; 
           [0017]      FIG. 2  is a cutaway side view of a single-bearing position encoder; 
           [0018]      FIGS. 3A-B  are cutaway side views of double-bearing position encoder embodiments incorporating a slotted wheel encoder; 
           [0019]      FIG. 4  is a cutaway side view of a double-bearing position encoder embodiment incorporating a reflective cylinder encoder; 
           [0020]      FIGS. 5A-B  are front and back perspective views of a double-bearing position encoder assembly; 
           [0021]      FIGS. 6A-B  are partially exploded and exploded perspective views, respectively, of a double-bearing position encoder assembly; 
           [0022]      FIGS. 7A-E  are top, front, bottom, side and perspective views, respectively, of an encoder mask block; 
           [0023]      FIGS. 8A-D  are top, perspective, front and side views, respectively, of an encoder mask; 
           [0024]      FIGS. 9A-D  are top, perspective, front and side views, respectively, of a slotted encoder wheel; 
           [0025]      FIGS. 10A-E  are top, perspective, front, back and side views, respectively, of an encoder front housing; 
           [0026]      FIGS. 11A-E  are top, perspective, front, back and side views, respectively, of an encoder back housing; 
           [0027]      FIGS. 12A-E  are top, bottom, perspective, front and side views, respectively, of an encoder flex circuit; 
           [0028]      FIGS. 13A-B  are top and bottom exploded views, respectively, of flex circuit optics and a corresponding encoder mask block; 
           [0029]      FIGS. 14A-B  are assembled and partially exploded perspective views, respectively, of another double-bearing position encoder assembly; 
           [0030]      FIGS. 15A-D  are front, perspective, top and side views, respectively, of an encoder mask block; 
           [0031]      FIGS. 16A-D  are front, perspective, top and side views, respectively, of an encoder mask; 
           [0032]      FIGS. 17A-B  are top and bottom exploded views, respectively, of flex circuit optics and a corresponding encoder mask block; 
           [0033]      FIGS. 18A-B  are front and back perspective views of a further double-bearing position encoder assembly; 
           [0034]      FIGS. 19A-B  are top and bottom partially exploded perspective views, respectively, of a further double-bearing position encoder assembly; 
           [0035]      FIGS. 20A-B  are top mostly exploded and exploded perspective views, respectively, of a further double-bearing position encoder assembly; 
           [0036]      FIGS. 21A-B  are front and perspective views, respectively, of a first encoder cylinder embodiment; 
           [0037]      FIGS. 22A-B  are front and perspective views, respectively, of a second encoder cylinder embodiment; and 
           [0038]      FIGS. 23A-B  are front and perspective views, respectively, of a third encoder cylinder embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Generally 
       [0039]      FIGS. 3-23  illustrate three position-encoder embodiments. Each of these embodiments advantageously utilize a double-bearing axle to stably mount an optical encoding device for the most precise optical measurements of the axle angular position and, hence, the linear position versus time of a pulser  140  ( FIG. 1 ). In this manner, a precisely measured and controlled sensor active pulse can be generated. 
         [0040]      FIGS. 3A-B  generally illustrate slotted-wheel, position-encoder  301 ,  302  embodiments. The encoders  301 ,  302  each have an axle  310  with a double-bearing  320  mount to a housing  330 . The slotted wheel  370  is mounted to the axle  310 . LEDs  340  illuminate a wheel obverse side and detectors  350  sense the illumination through wheel slots on a wheel reverse side. A folded, slotted mask  361  is positioned on both sides of the slotted wheel  370  so that mask slots align with wheel slots at discrete axle positions. Accordingly, axle position pulses are generated as the axle  310  rotates the wheel  340  and the wheel slots alternately block and pass light, as generated and sensed with the LED/detector optics  340 ,  350 . 
         [0041]    As shown in  FIG. 3A , the LED/detector optics  340 ,  350  are located perpendicular to the slotted wheel, and the mask  361  is reflective. A slotted wheel position encoder embodiment according to  FIG. 3A  is described in detail with respect to  FIGS. 5-13 , below. 
         [0042]    As shown in  FIG. 3B , the LED/detector optics  340 ,  350  are located parallel to the slotted wheel so as to directly illuminate and sense via the mask  362 . A slotted wheel position encoder embodiment according to  FIG. 3B  is described in detail with respect to  FIGS. 14-17 , below. 
         [0043]      FIG. 4  generally illustrates a reflective-cylinder, position-encoder  400  embodiment. The encoder  400  has an axle  410  with a double-bearing  420  mount to a housing  430 . A reflective cylinder  440  is mounted to the axle  410 . The cylinder surface has a repetitive reflective structure disposed across the length of the cylinder. A commercial optical encoder  450  is located over the cylinder so as to sense the reflective structure  440  and determine axle position accordingly. In an embodiment, the optical encoder is a 3-channel reflective incremental encoder available from Avago Technologies, San Jose, Calif. A reflective cylinder position encoder embodiment according to  FIG. 4  is described in detail with respect to  FIGS. 18-23 , below. 
       Slotted Wheel Encoder—Indirect Illumination Encoder Mask 
       [0044]      FIGS. 5-13  illustrate details of a double-bearing, slotted-wheel, position-encoder embodiment utilizing an indirectly-illuminated (indirect) encoder mask.  FIGS. 5-6  illustrate the double-bearing position encoder  500  assembly which reads an encoder wheel  900  via a wheel-edge-mounted photo interrupter  610 . The encoder wheel  900  is part of an encoder assembly  620 . The encoder assembly  620  is advantageously mounted within an double-bearing encoder housing  1000 ,  1100 . The photo interrupter  610  includes an encoder mask block  700  that houses a reflective encoder mask (origami)  800 , LEDs  1310  and detectors  1320 . The LEDs  1310  and detectors  1320  are mechanically mounted to, and in electrical communications with, a flex circuit  1200  that generates LED  1310  drive signals and receives and processes detector  1320  signals. The encoder assembly  620  has a encoder wheel  900  mounted between encoder wheel bushings  626  and shaft bushings  624 . The photo interrupter  610  is mounted onto the encoder housing  1000 ,  1100  over an encoder wheel  900  edge. 
         [0045]      FIGS. 7A-E  illustrate an encoder mask block  700  that houses the flex circuit-mounted optics  1310 ,  1320  ( FIGS. 13A-B ) proximate to the encoder mask  800  ( FIGS. 8A-D ).  FIGS. 8A-D  illustrate the encoder mask  800 , which defines an encoder wheel path  810 , reflective surfaces  820  and mask slots  830 . The encoder mask allows the LEDs/detectors  1310 ,  1320  ( FIG. 13B ) to read the wheel slots at 0 and 90 electrical degrees. In particular, LED  1310  ( FIG. 13B ) light is reflected off one surface  820  through the slots  830  and intermittently through the encoder slots  920  as the encoder  900  spins within the wheel path  810 . The intermittent light is reflected off another surface  820  to the detectors  1320  ( FIG. 13B ).  FIGS. 9A-D  illustrate a slotted encoder wheel  900  constructed as a thin, round disk defining a center-mount hole  910 , encoder slots  920  and an index slot  930 . 
         [0046]      FIGS. 10-11  illustrate the encoder front housing  1000  and back housing  1100  that advantageously provides a double-bear mount for the encoder assembly  620  ( FIGS. 6A-B ). Further the housing  1000 ,  1100  positions the photo interrupter  610  ( FIGS. 6A-B ) over the encoder wheel  900  so as to detect the passing encoder slots  920  ( FIGS. 9A-D ).  FIGS. 12-13  illustrate the encoder flex circuit assembly  1200  and corresponding optics  1300  and mask block  700 , which generate signals responsive to the encoder  900  ( FIGS. 9A-D ) position as it rotates in response to a shaft-coupled, motor-driven active pulser  110 ,  120 ,  140  ( FIG. 1 ). 
       Slotted Wheel Encoder—Direct Illumination Mask 
       [0047]      FIGS. 14-17  illustrate details of a double-bearing, slotted-wheel, position-encoder  1400  embodiment utilizing a direct illumination encoder mask.  FIGS. 15A-D  illustrate an encoder mask block  1500  that positions flex circuit-mounted optics to the mask  1600  ( FIGS. 16A-D ).  FIGS. 16A-D  illustrate the encoder mask origami  1600  having mask slots for reading the wheel slots at 0 and 90 electrical degrees.  FIGS. 17A-B  illustrate flex circuit optics  1700  and the corresponding encoder mask block  1500  ( FIGS. 15A-D ). 
         [0048]    As shown in  FIGS. 14A-B , a double-bearing position encoder  1400  assembly reads an encoder wheel portion of an encoder assembly  1420  via a wheel-edge-mounted direct illumination mask  1600  and proximate-mounted LED/detector optics  1700  ( FIGS. 17A-B ). The encoder assembly  1420  is advantageously mounted within an double-bearing encoder housing  1401 ,  1402 . A photo interrupter includes an encoder mask block  1500  that houses a direct illumination encoder mask  1600 , LEDs  1710  ( FIG. 17B ) and detectors  1720  ( FIG. 17B ). The LEDs and detectors are mechanically mounted to, and in electrical communications with, a flex circuit  1701  that generates LED drive signals and receives and processes detector signals. The encoder assembly  1420  has a encoder wheel mounted between encoder wheel bushings and shaft bushings as described above. The photo interrupter  1500 ,  1600  is mounted onto the encoder housing  1401 ,  1402  over an encoder wheel edge. 
         [0049]      FIGS. 15A-D  illustrate an encoder mask block  1500  that houses the flex circuit-mounted optics  1710 ,  1720  ( FIGS. 17B ) proximate to the encoder mask  1600  ( FIGS. 16A-D ).  FIGS. 16A-D  illustrate the encoder mask  1600 , which defines an encoder wheel path  1610 , a direct optical path  1620  and mask slots  1630 . The encoder mask allows the LEDs/detectors  1710 ,  1720  ( FIG. 17B ) to read the wheel slots at 0 and 90 electrical degrees. In particular, LED  1710  ( FIG. 13B ) light is directly transmitted  1620  through the slots  1630  and intermittently through the encoder slots  920  ( FIG. 9B ) as the encoder spins within the wheel path  1610 . The intermittent light is directly transmitted  1620  to the detectors  1720  ( FIG. 17B ). 
       Reflective Cylinder Encoder 
       [0050]      FIG. 18-23  illustrate details of double-bearing, reflective cylinder, position-encoder  1800  embodiment utilizing an off-the-shelf reflective encoder  1810  mounted proximate a double-bearing reflective encoder cylinder  2100 - 2300  ( FIGS. 21-23 ).  FIGS. 18-20  illustrate the double-bearing position encoder  1800  embodiment having an off-the-shelf reflective encoder  1810 , an encoder block  1820  and a reflective encoder cylinder  2100 - 2300 .  FIGS. 21-23  illustrate various encoder cylinder embodiments. 
         [0051]    A double-bearing position encoder has been disclosed in detail in connection with various embodiments. These embodiments are disclosed by way of examples only and are not to limit the scope of the claims that follow. One of ordinary skill in the art will appreciate many variations and modifications.