Apparatus for controlling rotational speed by optical data collection

Abstract: The apparatus is particularly suitable for controlling rotational speed of an inner housing (26) relative to an outer housing (12) in a centrifuge in which both housings rotate about a common axis. A reflector (58) is provided on the inner housing offset from the axis and an optic fibre (52) extends through the outer housing along the axis and terminates in the outer housing at a position offset from the axis to transmit radiation from a source (42) to impinge on the reflector. Reflected radiation is transmitted back down the optic fibre and is sensed by a sensor (66) as an indication of rotational velocity of the inner housing. A second sensor (74) senses the rotational speed of the outer housing (12) and a control system (70) compares the outposts of the sensors and controls the relative rotational velocities of the housings.

Description: Field of the Invention The invention pertains to non-contact systems, for collecting data off of a moving member and for bringing that data to a non-moving location. More particularly, the invention pertains to non-contact sensing systems usable with dual housing centrifuges wherein an outer housing is rotated at a first rotational velocity and an inner housing is rotated at a higher rotational velocity, usually twice that of the outer housing. Background of the Invention In recent years, processing of whole blood from a donor has come to routinely include separating the blood into therapeutic components. These components include red blood cells, platelets and plasma. Various techniques and apparatus have been developed to facilitate the collection of whole blood and the subsequent separation of therapeutic components therefrom. One consideration in the processing of whole blood is the requirement that the processing take place under sterile conditions. A second consideration involves the requirement that unless the processing takes place within a single sealed system, the permitted storage duration and usable lifetime of the blood components is substantially shortened. Components processed within a sealed system can be stored for four to six weeks or longer before use. On the other hand, whole blood or components thereof must be used within 24 hours if the system seal is broken. One very common step in the processing of whole blood into various therapeutic components includes centrifuging the blood so as to bring about the desired separation of those components. To promote the desired ends of sterile processing within a single sealed system, a family of dual housing centrifuges has been developed. One example of this type of centrifuge is disclosed in United States Patent No. RE 29,738 to Adams entitled "Apparatus for Providing Energy Communication Between a Moving and a Stationary Terminal." The Adams patent discloses a centrifuge having an outer rotatable housing and an inner rotatable housing. The inner housing is positioned within and rotatably supported by the outer housing. The outer housing rotates at one rotational velocity, usually called one omega, and the inner rotatable housing rotates at twice the rotational velocity of the outer housing or two omega. There is thus a one omega difference in rotational speed of the two housings. The centrifuge of the Adams patent is particularly advantageous in that no seals are needed between moving and non-moving parts. Further, the system of the Adams patent, provides for the processing of blood into components in a single sealed system wherein whole blood from a donor can be infused into the centrifuge while the two housings of the centrifuge are being rotated. The system of the Adams patent uses a single motor coupled by gears and shafts to the two housings so as to provide the desired speed synchronization. This is an open loop system. While the centrifuge of the Adams patent provides an apparatus wherein blood processing may take place in a single sealed sterile system, the mechanical apparatus of the Adams patent is subject to wear of the type normally experienced with gear driven systems. Hence, centrifuges in accordance with Adams disclosure must be built as precision mechanical systems. Since it is an open loop system, care must be exercised to insure that the two chambers do in fact continually operate at the desired speeds. An alternate to the mechanical apparatus of the Adams patent is illustrated in United States Patent No. 4,056,224 to Lolachi entitled "Flow System for Centrifugal Liquid Processing Apparatus." The system of the Lolachi patent includes a dual chamber centrifuge of the Adams type. The outer housing of the Lolachi centrifuge is rotated by a single electric motor which is coupled to the internal rotatable housing by belts and shafts. The Lolachi mechanism, as was the case with the Adams mechanism, is an open loop, essentially mechanical, structure for driving the two rotatable housings. United States Patent Nos. 3,986,442 and 4,113,173 illustrate alternate, open loop drive systems. United States Patent No. 4,108,353 to Brown entitled "Centrifugal Apparatus With Oppositely Positioned Rotational Support Means" discloses a centrifuge structure of the Adams type which includes two separate electrical motors. One electric motor is coupled by a belt to the outer housing and rotates the outer housing at a desired nominal rotational velocity. The second motor is carried within the rotating exterior housing and rotates the inner housing at the desired higher velocity, twice that of the exterior housing. Tachometer feedback is provided from the second motor through a set of slip rings or brushes for the purpose of continuously controlling the speed of the second motor with respect to the first motor. The structure of the Brown patent thus provides for obtaining electrical signals corresponding to the velocity of the inner motor for the purpose of continually controlling the speed thereof by means of a closed loop control system. US-A-4,109,855 discloses yet another drive system, which has an outer shaft, affixed to the outer housing for rotating the outer housing at a selected velocity. An inner shaft, coaxial with the outer shaft, is coupled to the inner housing. The inner shaft rotates the inner housing at twice the rotational velocity as the outer housing. The mechanism is an open loop system. A further alternate to the Adams structure is illustrated in WO-A-85/02560 (US-A-4,530,691). The centrifuge of this document also is of the Adams-type. However, this latter centrifuge has an exterior housing which is hinged for easy opening. When the hinged upper section is pivoted away from the bottom section, it carries the rotatable inner housing along with it. The inner housing supports internally therein a spring biased mandrel which continually presses against a sealed, blood containing, container positioned within the inner housing. The system also discloses the use of two separate electric motors to rotate the inner and outer housings. The motors are coupled to a control system. Thus, while it is known from the prior art to use two independent motors in connection with a control system to rotate the dual housings of an Adams-type centrifuge, there are no known non-contact systems for acquiring or collecting velocity information from the inner rotating housing. Additionally, none of the prior art systems have provided control information concerning the direction of rotation of the inner housing. EP-A-0112143 discloses a gyroscope and is concerned with controlling the speed of a gyroscopic rotor. The document discloses an apparatus for controlling the relative speed of rotation of inner and outer members, the inner member being rotatably supported by the outer member, the apparatus including a source of radiant energy, reflecting means on the inner member, means for transmitting at least a portion of the radiant energy to a region of the inner member so as to be incident on the reflecting means, means for sensing radiant energy reflected from the reflective means for generating a first electrical signal indicative of rotational speed of the inner member, and control means for controlling said relative speed of rotation in response to the first signal. The reflecting means lies parallel to the axis of rotation of the inner member, which is a shaft, and the radiation impinges on the reflective means in a direction normal to the axis of rotation. US-A-3982162 discloses an analytical centrifuge which does not have an inner rotating housing. The rotational velocity of the single rotatable housing disclosed is controlled by means of a reflective data ring on the housing. A light beam is made incident on the ring and a light sensor is located to receive the reflected light to sense the velocity of the housing. The present invention relates to apparatus as set in the precharacterising part of Claim 1 based on the disclosure of WO-A-85/02560. The distinguishing features of the invention are set out in the characterising part of Claim 1. The invention provides an apparatus comprising a rotatable outer member (12), an inner member (26) rotatably supported by the outer member, means (14,22) for driving the members (12,26) about a common axis at different rotational speeds, and means (112) for controlling the relative speed of rotation of the members, characterised by a source of radiant energy (42), reflecting means (58) spaced from the common axis and provided on the inner member (26), transmission means located at least in part along the axis of rotation to transmit at least a portion of the radiant energy to a region of the inner member so as to be incident on the reflecting means (58), and to transmit radiant energy reflected from the reflecting means to first sensing means (66,272) for sensing the reflected radiant energy, the first sensing means generating a first electrical signal indicative of rotational speed of the inner member (26), second sensing means (74) for sensing the speed of rotation of the outer member (12) and provide a second electrical signal indicative thereof, comparing means (104,106) to compare the first and second signals with each other, or with predetermined, derived rotational velocities for the motors (14,22), and means (112) responsive to the comparing means to controlling the drive means, so as to control the relative rotational speed of the inner and outer members (12,26). In a particular apparatus in accordance with the invention, the transmission means can be a bidirectional fiber-optic member. Radiant energy can be transmitted to or received from the moving member via the fiber optic-member. The reflector elements can be a plurality of mirrors spaced-apart and affixed to the moving member. The mirrors are separated by non-reflecting members. Radiant energy reflected off the mirrors is transmitted to the fixed location by the fiber-optic member as a series of radiant energy pulses. A detector converts the series of radiant energy pulses to an electrical pulse train. The rate of the pulse train is proportional to the rotational velocity of the moving member. Control circuitry compares the rate of the pulse train to a set-point value corresponding to a pre-determined velocity. An error signal, corresponding to the difference therebetween, can be used to drive velocity control circuitry. The velocity control circuitry can be used to adjust the rotational velocity of a prime move, an electric motor, coupled to the moving member. Alternatively, a proportional-integral-differential control system could be used. This system provides for control of the displacement of the moving member. In yet another apparatus in accordance with the invention, the reflector elements can include elements of two different colors, such as red and green. If the different colored elements are alternately positioned along the movable member and if separate detectors are provided for reflected red and reflected green light, two sets of pulse trains can be generated. The two sets of pulse trains can be processed, as is known in the art, to determine direction of movement in addition to velocity. In yet another embodiment of the invention, the fiber optic members can be replaced with a Dove prism. A Dove prism will rotate an image transmitted therethrough twice for each rotation of the prism. If the prism is positioned in the axis of rotation of the first member, it will project an image of a selected region of the second member onto the optical detector. If the second member is rotating at twice the velocity of the first member, the transmitted image will be stationary when it impinges on the detector. If the relative velocity between the two members varies from the 2:1 relationship, the image will move relative to the detector. A quadrature detector can be used to convert this movement to electrical signals. The electrical signals can be used to provide input to a control system which can then be used to control the relative speed of the two members. Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings in which the details of the invention are fully and completely disclosed as a part of this specification. Description of the Drawings FIGURE 1 is a view in section of an Adams-type centrifuge incorporating two independent drive motors and a fiber-optic based optical system in accordance with the present invention; FIGURE 2 is a fragmentary, enlarged schematic view of a data ring usable with the centrifuge of Figure 1; FIGURE 3 is a block diagram of a velocity control system usable with the centrifuge of Figure 1; FIGURE 4 is a fragmentary, sectional view of another centrifuge in accordance with the present invention; FIGURE 5 is a fragmentary, enlarged schematic view of an alternate data ring usable with the centrifuge of Figure 4; FIGURE 6 is a block diagram of a portion of an alternate control system usable with the centrifuge of Figure 4; FIGURE 7 is a fragmentary view in section, illustrating a centrifuge including a liquid interface sensor; FIGURE 8 is a plan view of an alternate data ring usable with the centrifuge of Figure 7; FIGURE 9 is a view in section of an Adams-type centrifuge incorporating two independent drive motors and a prism based optical system in accordance with the present invention; and FIGURE 10 is a schematic view partly in perspective illustrating various optical characteristics of the prism of Figure 9. Detailed Description of the Preferred Embodiments While this invention is susceptible of embodiment in many different forms, there are shown in the drawing and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. With respect to the figures, Figure 1 illustrates a centrifuge 10 with an outer rotary housing 12 which is mechanically coupled to an electric drive motor 14. The motor 14 can be a commercially available, pancake-type motor. The motor 14 has a stationary magnet 14a positioned adjacent a pancake armature 14b. The motor 14 rotates the housing 12 about an axis A-A. A hollow shaft 16 couples the armature 14b of the motor 14 to the rotary housing 12. The shaft 16 passes through a bearing structure 18 which provides rotary support for the housing 12. A stationary disk-shaped plate 19 is attached to the bearing structure 18 below the rotary housing 12. The rotary housing 12 has an upper portion 12a which is coupled to a lower portion 12b by a hinge 12c. As is illustrated in the above incorporated Brown patent, the upper portion 12a of the housing 12 can be rotated from a closed position, as illustrated in Figure 1 to an open position by rotation of the upper section 12a about the hinge 12c. Affixed to an upper member 20 of the housing section 12a is a second pancake-type electric motor 22. The motor 22 has a shaft 24 which rotates about an axis A′-A. The axis A-A, A′-A′ as illustrated in Figure 1 coincide. Coincidence of the axis A-A, A′-A′ is not a requirement of the present invention. It would be within the spirit and scope of the present invention to space the axis A-A, A′-A′ apart from one another. Affixed to the shaft 24 is a second, inner, housing 26. The housing 26 is rotated within the housing 12 by the motor 22. A bearing structure 30 provides rotating support for the housing 26. The inner housing 26 is also formed of two separable sections. An upper section 26a, as illustrated in Figure 1, is affixed to the shaft 24. A lower, removable section 26b is removable affixed to the upper section 26a by a flexible clamp 32. A spring loaded mandrel 34 is positioned within the housing 26. The mandrel 34 is downwardly biased, as illustrated in Figure 1, by a biasing spring 36. Further detail of a mechanical nature of the centrifuge structure 10, are disclosed in the above-identified and incorporated Brown patent. It is important, as taught in that Brown patent, to rotate the inner housing 26 at twice the rotational velocity of the outer housing 12. It will also be understood that the housing 26 could be rotatably mounted above the housing 12 without departing from the spirit and scope of the present invention. In order to provide for dynamically determining the rotary velocity or the speed of rotation of the housing 26 while the housing 12 is being rotated, an optical system 40 is provided. The optical system 40 includes a source of radiant energy, such as an electric light, 42 which generates a beam of radiant energy which passes through a lens 44. The focused light beam 46, after exiting the lens 44, enters a beam splitter 48. The purpose of the beam splitter 48 is to direct a portion of the beam 46 upwardly along the axis A-A and into an end 50 of a fiber-optic radiant energy transmitting member 52. The fiber-optic member 52 functions as a bidirectional means for transmission of radiant energy. The fiber-optic member 52 is affixed to the hollow, rotating shaft 16 and centrally located with respect thereto along the axis of rotation A-A. As the shaft 16 rotates, and in turn rotates the housing 12, the fiber-optic member 52 also rotates. Radiant energy 46 which is deflected off of the beam splitter 48 into the lower end 50 of the fiber-optic member 52 is transmitted with essentially little or no losses to an upper end 56. The upper end 56 is positioned within the housing 12 adjacent a selectively reflecting member 58. The reflecting member 58 is affixed to a lower surface 60 of the housing member 26b. The selectively reflecting member 58 can be thought of as a data ring. Radiant energy which exits from the end 56 of the fiber-optic member 52 is directed toward the data ring 58. A mechanical support 62 positioned within the rotary housing 12 rigidly maintains the end 56 of the fiber-optic member 52 adjacent the data ring 58. Radiant energy which exits from the end 56 and which falls upon the data ring 58 is selectively reflected off the data ring 58 back into the end 56. The reflected radiant energy 64 passes through the fiber-optic member 52, exits the lower end 50 thereof, passes through the beam splitter 48 and impinges upon a photo detection unit 66. The photo detection unit 66 is electrically coupled via lines 68 to control system 70. Thus, as the housing members 12 and 26 rotate with respect to the fixed photo detector 66, a train of pulses of radiant energy, reflected off of the data ring 58, is transmitted through the fiber-optic member 52 and beam splitter 48 and impinges upon the photo detector 66. Information concerning the rotational velocity of the housing 26 with respect to the housing 12 may be collected and transmitted by the fixed photo detector 66 to the control system 70 for subsequent processing. The speed of rotation of the shaft 16 of the outer electric motor 14 may be sensed by affixing a tachometer disk 72 to an end of the shaft 16. As the disk 72 rotates, a second detector 74 can be used to sense its speed of rotation and generate electrical pulses proportion thereto on line 76. As will be discussed subsequently, one of the advantages of the apparatus of the present invention is that the rotational velocity of the housing 12 and the rotational velocity of the housing 26 may both be precisely controlled such that the housing 26 rotates at twice the velocity of the housing 12. Control is achieved by means of a closed loop system that does not utilize belts, gears and pullies as in many of the known prior art systems. Since the speed of each of the motors 14 and 22 can be precisely and independently controlled, without the need of any mechanical linkages therebetween, the required mechanical tolerances of the system 10 are reduced. Further, the speed control of the motors 14 and 22 is not affected by mechanical wear of the type that might occur between gears, belts or other linkages if the two motors were mechanically coupled together. With respect to Figure 2, the data ring 58 is illustrated in detail. Data ring 58 is formed of a plurality of spaced-apart reflective members 80 through 86. The members 80 through 86 are spaced apart and affixed to the lower surface 60 in a ring about the axis of rotation A′-A′. Between each of the reflective members 80 through 86 is a non-reflective or blackened region 90 through 96. The beam of radiant energy is illustrated in Figure 2 impinging upon a region of the data ring 58. As the ring 58 rotates and the reflective members 80 through 86 pass over the beam 46, a portion of that beam is reflected back into the end 56 of the fiber-optic member 58 and is retransmitted through the beam splitter 48 into the detector unit 66. An electrical pulse train corresponding to the pulse train of radiant energy retransmitted through the member 52 is then generated on the lines 68. While the members 80 through 86 are preferably high reflective mirrors, they could also be formed on the surface 60 by polishing the surface 60 and darkening alternate regions thereof, for example by anodizing, so as to form the members 90 through 96. Figure 3 illustrates schematically the control system 70. The control system 70 includes circuits 100 for conditioning the electrical pulses on the lines 68, corresponding to the relative rotational velocity of the housing 26 with respect to the housing 12. A second set of conditioning circuits 102 is coupled to the lines 76 to condition the electrical pulse train corresponding to the rotational velocity of the housing 12. The conditioning circuits 100 and 102 provide, respectively, inputs to comparison circuits 104 and 106. Set point inputs 108 and 110 specify predetermined, desired, rotational velocities for the motors 22 and 14, respectively. Error signals from the comparison circuits 104 and 106 are amplified in a set of motor control amplifiers 112 so as to provide outputs to the two motors. The control system 70 of Figure 3 will provide velocity error signals to the amplifiers 112 so as to maintain the rotational speed of the housing 26 at twice the rotational speed of the housing 12. The data ring 58 will not provide any information as to direction of rotation of the housing 26. As an alternate to the control system 70 of Figure 3 which provides for velocity control of both motors 14 and 22, electrical energy can be supplied to motor 14 so that it will operate, open loop, at about its nominal rotational speed. Velocity feedback signals on the lines 76 can be used as the set-point input to the comparison circuit 104. the error signal input to the amplifiers 112 can then be adjusted to cause the motor 22 to operate at twice the rotational velocity of the motor 14. While the control system 70 has been illustrated in block diagram form in Figure 3, it will be understood that the exact implementation thereof is not a limitation of the present invention. For example, control system 70 could be implemented in hardwired form. Alternately, a commercially available micro-processor could be used to implement the control system 70. It will also be understood that the control system of Figure 3 could be implemented as a proportional-integral-differential (PID) system. In such an implementation, not only could the velocity of the inner housing 26 be controlled, but the relative displacement between the outer housing 12 and the inner housing 26 could also be precisely controlled. Figure 4 illustrates an alternate embodiment of the system 10. In Figure 4, elements which correspond to the elements of Figure 1 are given the same identification numerals. The system 120 of Figure 4 includes the source of radiant energy 42 which generates visible white light, the beam splitter 48 which was present in the system 10 and two additional beam splitters 122 and 124. Associated with each of the beam splitters 122, 124 is a color-coated filter such as a green filter 128 and a red filter 130. Associated with each of the respective filters 128 and 130 is a corresponding optical detector 132 and 134. Outputs from the detectors 132 and 134 are coupled via the lines 136 and 138 to a control system 140. The dual color detecting scheme of the system 120, as illustrated in Figure 4, operates in conjunction with a data ring 142 which is affixed to the lower surface 60 of the housing 26b. The detectors 132 and 134 are adapted to generate an electrical pulse train in response to sensing a beam of a selected frequency. By means of the filters 128 and 130, selected sequences of green or red radiant energy pulses can be detected. The data ring 142, as illustrated in Figure 5, includes a plurality of spaced-apart, green reflective regions 150 through 154. In addition, the ring 142 includes a plurality of spaced-apart, red reflective regions 160 through 164. As the housing 26 rotates the incident beam 46 falls on the green reflective members alternately with falling on the red members. Green and red pulses of reflected radiant energy are transmitted back through the bidirectional member 52. The reflected green an red pulses pass through the respective green and red filters 128 and 130 and are detected by respective detectors 132 and 134. The sequence of detected red or green radiant energy pulses provides the same type of velocity information as is provided by the pulse train of the system 10 of Figure 1. Additionally, since two sets of spaced-apart pulse trains are generated on the lines 136 and 138, the direction of rotation of the housing 26 can also be determined. If desired, the data ring 142 can include reflective members 170 through 174 corresponding to the reflective members 80 through 84 of Figure 2. The reflective members of the data ring 142 are also spaced apart by a plurality of non-reflective members 180 through 184. The light beam reflected off of the mirrors 170 through 174 can be sensed by the redundancy detector 190 if desired. The motor control circuitry 140 of Figure 6 illustrates that portion of the control circuitry necessary to adjust the speed of the motor 22. The speed of the motor 14 is still adjusted using the circuitry previously discussed in Figure 3. Pulses from the green photo detector 132 and the red photo detector 134 are conditioned by circuits 200 and 202, respectively. Outputs from the conditioning circuits 200 and 202 are utilized by direction sensing circuitry 204 to generate a directional output on a line 206. Analogously to the control system of Figure 3, a pulse train generated by the conditioning circuits 202 on lines 208 provides inputs to comparison circuitry 210. The pulse rate corresponding to the pulses from the red photo detector 134 is compared to a set point input 212. An error signal is then generated on lines 214. The error signal on the lines 214 is a velocity error signal which provides input to motor control circuitry 216. The motor control circuitry 216 in turn can be used to adjust the rotational velocity of the motor 22. Figure 7 illustrates yet another embodiment of the present invention. Elements of Figure 7 which correspond to elements of Figure 1 have again been given the same identification numerals. Figure 7 illustrates a system 220, usable as discussed in the above-incorporated Brown patent for the purpose of separating blood into red blood cell and plasma components. As is described in the above-incorporated Brown patent, after the container of whole blood has been positioned between the mandrel 34 and the lower part 26b of the housing 26, as the housing 26 is rotated, the blood will separate into packed red blood cells and plasma. The separation into components is illustrated schematically in Figure 7. During the separation process, when the red blood cells have been driven to the sides of the housing 26b, as illustrated in Figure 7, and away from the plasma component, a visible optical interface is present therebetween. By means of the system 220 this interface can be optically detected. An optical system of the general type used in system 10 transmits a beam of radiant energy to a data ring 222 which is affixed to the lower surface 60 of the housing portion 26b. In the system 220, the lower housing member 26b would preferably be formed of a transparent plastic material. The mandrel 34 has a highly-polished, mirrored surface, or a mirror 224 is affixed to a lower surface 226 generally above the data ring 222. The mirrored surface, or the mirror, 224 could be formed as a circular ring on the lower surface 226 of the mandrel 34. As illustrated in Figure 7, the interface between the plasma and the packed red blood cells is located between the data ring 222 and the reflecting surface or mirror 224. Radiant energy from the fiber-optic member 52 will pass through the region of plasma to the mirrored surface 224 but will not pass through the packed red blood cells. Hence, provided the data ring 222 has a transparent region or regions, radiant energy from the end 56 of the fiber optic member 52 can be transmitted through the transparent region or regions of the data ring 222, and then through the plasma provided the interface is located as shown in Figure 7 to impinge upon the mirrored surface 224. The radiant energy that impinges on the mirrored surface 224 will be reflected back through the plasma, through the data ring 222 and back through the fiber-optic member 52 to the detector 66 where it will be converted to a usable electrical signal. The electrical signal corresponding to the liquid interface being positioned between the data ring 222 and the mirrored region 224 can be used to operate valves and/or visual indicators for purposes of operator control. Figure 8 illustrates the exemplary data ring 222. The data ring 222 can include a plurality of spaced-apart reflecting members such as the members 230 and 232. The members 230 and 232 correspond to the spaced-apart members 80 through 86 of Figure 2 and can be used to determine the rotational velocity of the housing 26. A longer mirrored region 240 can be provided for the purpose of generating a start or strobe signal to be used by the control system. Further, a clear region 242 can be provided wherein the interface between the plasma and the red blood cells will appear and can be detected. The precise location of the interface between the plasma and the packed red blood cells, with respect to the clear region 242, will vary the amount of radiant energy or light reflected from the mirrored surface 224. As illustrated in Figure 8, the reflecting members and the clear member 242 can be spaced apart by a plurality of black or absorbing regions 250 through 256. In addition, the data ring 222 can be provided with additional clear regions such as the region 260. Further, mirrored regions of various sizes such as the regions 262 and 264 can be provided to generate special control signals. The regions 262 and 264 can be spaced apart by non-reflective regions such as the region 266, which are substantially longer than the non-reflective regions 250 through 256. In addition, if desired, the data ring 222 could be provided with a plurality of spaced-apart red or green reflective regions as in the data ring 142 of Figure 5. In this configuration, in addition to sensing the presence or absence of the interface between the plasma and the red blood cells, the direction of rotation of the housing 26 can also be determined. Yet another alternate embodying the present invention is illustrated in Figure 9. A system 250 includes the dual, rotatably mounted housings 12 and 26. The exterior housing 12 is rotated by a pancake motor 252. The motor 252 includes a fixed ring magnet 252a and a rotatable pancake amature 252b. The armature 252b is mechanically affixed to a rotatable, hollow shaft 254 which rotates about an axis B-B. The shaft 254 is mechanically affixed to the lower portion 12b of the housing 12. A bearing assembly 256 rotatably supports the shaft 254. The motor 252, in Figure 9, is positioned above the bearing assembly 256. A seal 258 is positioned between the rotatable shaft 254 and the motor 252. While the bearing assembly 256 is located below the motor 252 in the system 250, as opposed to the arrangement of Figure 1 wherein the bearing assembly 18 is located above the motor 14, it will be understood that the exact arrangement of the bearing assembly with respect to the exterior motor is not a limitation of the present invention. A Dove prism 260 is positioned within the hollow shaft 254. The optical axis of the Dove prism 260 corresponds to the axis of rotation B-B of the shaft 254. The source of radiant energy 42 and focusing lens 44 generate the beam of radiant energy 46. The beam of radiant energy 46 is bent 90 degrees by the beam splitter 48 and directed along the axis B-B into the Dove prism 260. When the beam 46 exits the prism 260, it passes through a deflecting lens 262. The lens 262 deflects the beam 46 so that it is incident on a mirror 264 which is affixed to a lower surface 60 of the lower housing portion 26b. Radiant energy reflected off of the mirror 264 returns to the lens 262 and impinges upon the prism 260. The beam travels along essentially the same path, exiting at the lower end of the prism 260. The reflected beam then passes through the beam splitter 48, through a focusing lens 270, and impinges upon a quadrature detector 272. The image reflected onto the quadrature detector 272 causes that detector to generate electrical signals in response thereto. Those electrical signals generated by the quadrature detector 272 on lines 274 can be used as inputs to a control system or control circuitry 276. It is a recognized characteristic of Dove prisms that if the prism is rotated about its optical axis once, an image transmitted therethrough will be rotated twice. In the present instance, if the members 26 and 12 have the desired 2:1 velocity relationship for each rotation of the dove prism 260, the mirror 262 will have rotated twice. Hence, the image incident on the quadrature detector 272 will appear to be stationary. Any variation in the 2:1 rotational velocities between the housings 26 and 12 will manifest itself in movement of the image on the quadrature detector 274 in one direction or another. Movement of the image on the quadrature detector 272 will cause a change in the electrical signals on the lines 274 which can be sensed by the control circuitry 276. Output from the control circuitry 276 on the lines 278 can be communicated to the upper motor, corresponding to the motor 22 of Figure 1, via a set of slip rings 280 affixed to the rotatable shaft 254. Leads 282 located within the rotary housing 12 can be coupled to the upper motor 22 for the purpose of providing electrical control signals thereto. The control circuitry 276 can be the general type as illustrated in Figure 3. In this embodiment, the set point input on the lines 108 would correspond to a desired reflected image position on the quadrature detector 272. Alternately, the control system 276 could be implemented as the above-noted proportional-integral-differential control system. Figure 10 is a further illustration of the characteristics of the dove prism. The use of the dove prism 260 in the system 250 provides a solid state stroboscope which generates a stationary image on the quadrature detector 272 when the upper housing 26 is rotating at exactly twice the rotational velocity of the outer housing 12. Figure 10a depicts a Dove prism which is nothing more than a right angle prism with its point cut off. An object viewed through a Dove prism appears to be inverted in one axis but not the other -- much like a mirror except that the mirroring effect is in line as opposed to reflex. Figure 10b illustrates the effect. An object arrow appears inverted when viewed through the Dove prism. If the object is rotated through some angle "A", it appears to be rotated in the opposite direction when viewed through the prism as shown in Figure 10c. If the object remains stationary and the prism is rotated through some angle "A", the object appears to rotate through an angle "2A" in the same direction as illustrated in Figure 10d. Finally, it has been observed and can be mathematically shown that if the object is rotated through an angle "2A" while the prism is rotated through an angle of just "A" as shown in Figure 10e, the object does not appear to rotate at all. In yet another alternate instead of an optical system, a transmitter 290, indicated in phantom affixed to the top of the motor 22 of Figure 1 could be used to transmit velocity information to a fixed location. Velocity information concerning the speed of rotation of the housing 26 could be generated by affixing a tachometer disk 292, also shown in phantom, to the shaft 24. Similarly, the location of the optical interface between the plasma and the packed red blood cells could be detected and transmitted to the fixed location. The transmitter 290 could be an infra-red or a radio-frequency transmitter. A stationary receiver, outside of the housing 12, could be used to detect the transmitted signals. The detected signals could be converted to electrical signals and supplied to a control system such as the control system 70. It will be understood that the exact form of the source of radiant energy 42 is not a limitation of the present invention. For example, the source 42 could be an incandescent lamp. In this instance, the beam of radiant energy 46 would be a beam of visible light.

Claims: An apparatus comprising a rotatable outer member (12), an inner member (26) rotatably supported by the outer member, means (14,22) for driving the members (12,26) about a common axis at different rotational speeds, and means (112) for controlling the relative speed of rotation of the members, characterised by a source of radiant energy (42), reflecting means (58) spaced from the common axis and provided on the inner member (26), transmission means located at least in part along the axis of rotation to transmit at least a portion of the radiant energy to a region of the inner member so as to be incident on the reflecting means (58), and to transmit radiant energy reflected from the reflecting means to first sensing means (66,272) for sensing the reflected radiant energy, the first sensing means generating a first electrical signal indicative of rotational speed of the inner member (26), second sensing means (74) for sensing the speed of rotation of the outer member (12) and providing a second electrical signal indicative thereof, comparing means (104,106) to compare the first and second signals with each other, or with predetermined, derived rotational velocities for the motors (14,22), and means (112) responsive to the comparing means for controlling the drive means, so as to control the relative rotational speed of the inner and outer members (12,26). Apparatus according to Claim 1, wherein said reflecting means (58) includes a plurality of spaced apart reflective members (80 to 86 or 150 to 154) formed in a ring about the axis of rotation, whereby said reflective members, one after the other, receive incident radiant energy as the inner member (26) is rotated Apparatus according to Claim 1 or 2, wherein the transmitting means includes a fiber-optic member (52) or a prism (260). Apparatus according to Claim 3, wherein said fiber-optic (52) or prism (260) is bidirectional. Apparatus according to Claim 4, wherein said prism is a Dove prism. Apparatus according to Claim 5, wherein said Dove prism (260) projects a stationary reflected image onto said sensing means (272) only when said inner member (26) has a rotational velocity twice that of said outer member (12). Apparatus according to Claim 6, wherein said control means includes means for detecting movement of the image reflected onto said sensing means and means (276) for adjusting the speed of rotation of said outer or said inner member to minimize said image movement. Apparatus according to any preceding claim wherein said control means includes means (206) for determining a direction of rotation of said inner member. Apparatus according to Claim 8, including second reflecting means (160 to 164), affixed to said outer member for transmitting reflected radiant energy to said sensing means, said control means (140) determining the direction of rotation from signals derived from the reflected radiant energy from the first and second reflecting means. Apparatus according to Claim 9 as appendant to Claim 2, wherein said second means includes a second plurality of reflective members (160 to 164) interspersed with the first plurality (150 to 154) and said sensing means includes first and second means (132, 134) for detecting first and second beams of radiant energy reflected respectively from said first and said second pluralities of reflective members. Apparatus according to Claim 1 or 2, wherein the inner member (26) has a chamber (60, 26b) for containing a fluid whereby rotation of the inner member may cause separation of the fluid into components whereby an interface is defined between the components, the apparatus including means to detect the interface comprising a reflective element (224) on the inner member (26) with the chamber having a portion between the reflecting means (222) and the reflective element (224), the reflecting means (222) having a transparent portion permitting radiation to pass therethrough to the reflective element to detect an interface in fluid therebetween and to permit reflected radiation to pass through the reflecting means, and a sensor (66) for receiving the reflected radiation.

Inventors: BROWN RICHARD I, FOLEY JOHN T, BROWN, RICHARD I., FOLEY, JOHN T.
Applicants: BAXTER INT, BAXTER INTERNATIONAL INC.
Application year: 1986
Main classification: G01P3
IPC codes: G01P3