Apparatus for Transferring Data to and From a Moving Device

This invention relates generally to data communications, and more particularly to apparatus for transferring data to and from a rotating device.

It is well known to use electro-mechanical slip rings, to enable the transfer of data to and from a rotating device, such as the drum that is rotatably mounted in the gantry of a computer tomography (CT) scanner so that the X-ray equipment supported by the drum can be rotated about a patient during a tomographic scan. However, over long periods of use, mechanical wear and contamination can occur, leading to reduced electro-mechanical contact reliability, possibly resulting in loss of data. Further, where the rotating device is relatively large, such as the drum of a CT scanner, the use of commensurately large slip rings adds significant weight to the total weight of the CT scanner.

In addition, where the rotating device, such as a rotatable drum of a CT scanner, rotates a limited amount with each use, it is also known to transfer data to and from the drum through cables, which are wound and unwound as the device alternately rotates clockwise and counterclockwise. Again, disadvantages include additional weight due to the use of cables, the effects of the attached cables on the rotation of the rotating device, and decreased reliability due to, for example, the vulnerability of cables to disconnection and breakage when the cables are repeatedly wound or overwound.

U.S. Pat. Nos. 4,928,283 and RE 34,379 briefly describe a CT scan system employing a "two-way communication link" between "an electronics package" secured to the disk of the machine and a "computer used for image processing and control". No further detail is provided.

It is a general object of the present invention to provide an apparatus for transferring data to and from a moving device that significantly overcomes the problems of the prior art.

A more specific object of the present invention is to provide an apparatus for transferring data to and from a rotating device through a medium which is not required to be mechanically connected to the device as it rotates about its axis.

A further object of the present invention is to allow a rotating device to rotate for an extended period of time, allowing data to be transferred to and from the device at any time during the extended period.

Another object of the invention is to provide an apparatus for reliably transferring data to and from a rotating device without the use of cables or slip rings.

And another object of the invention is to provide a light weight apparatus for reliably transferring data to and from a rotating device, and particularly useful in CT scanners so as add little weight to the scanner.

Yet another object of the invention is to provide apparatus, particularly useful in CT scanners, for reliably transferring data to and from a rotating device with relatively low power consumption.

Still another object of the invention is to provide an apparatus for transferring data to and from a rotating device and particularly useful in CT scanners, while being significantly unaffected by electromagnetic interference.

And yet another object of the invention is to provide an apparatus for transferring data to and from a rotating device at relatively high data transfer rates, and being particularly useful in CT scanners.

And still another object of the invention is to provide an apparatus for transferring data to and from a rotating device at relatively low data error rates, and being particularly useful in CT scanners.

Other objects of the present invention will in part be suggested and will in part appear hereinafter. The invention accordingly includes the apparatus possessing the construction, combination of elements, and arrangement of parts, all of which are exemplified in the following detailed disclosure and the scope of the application, all of which will be indicated in the claims.

An apparatus is provided for transferring data between a first device and a second device that rotates with respect to the first device. The first device preferably is stationary and includes a fixed, stationary antenna assembly and a fixed transceiver for transmitting and receiving signals within a preselected part of the electromagnetic spectrum via the stationary antenna assembly as the second device rotates relative thereto. The rotating device preferably includes a rotating antenna assembly and a rotating transceiver for transmitting and receiving the signals via the rotating antenna assembly to and from the stationary antenna assembly. The rotating antenna assembly is mounted circumferentially about the rotating device such that the stationary antenna assembly is capacitively coupled to the rotating antenna assembly regardless of the instantaneous angular position of the rotating device.

In the preferred apparatus of the invention, data is transferred from the stationary device to the rotating device by encoding and modulating the data within the stationary transceiver, and then transmitting the encoded and modulated data within the preselected part of the electromagnetic spectrum from the stationary antenna assembly to the rotating antenna assembly via an air gap therebetween. The rotating transceiver receives the encoded and modulated data, and then at least demodulates and decodes it to extract the original data. Data is communicated from the rotating device to the stationary device in the same manner.

In a preferred embodiment, where more data is transmitted from the rotating device to the stationary device, data is transmitted from the stationary device to the rotating device via a single channel, and data is transmitted from the rotating device to the stationary device via two time-multiplexed channels so as to provide high speed data transfer from the rotating device to the stationary device.

The invention includes a variety of features for significantly reducing error rates, and particularly for reducing errors due to cross talk between channels. For example, the data can be transferred at a signal-to-noise ratio of less than about 20 dB. The invention provides data error rates which are significantly better, such as about one error in five trillion bits. In a preferred embodiment, to reduce cross talk, data is transferred using frequency shift keying (FSK), wherein the frequencies employed for modulating data transferred from the stationary device to the rotating device are different from the frequencies used for modulating data transmitted from the rotating device to the stationary device. Channel separation is further improved by spatially separating the antennas of the two channels used for "down link" transmission from the rotating device to the stationary device. Also, grounded conductors separate the down link from the "up link" channels. To reduce errors due to geometric and mechanical imperfections of the rotating device relative to the stationary device, the antenna assembly on the rotating device is adapted to remain in capacitive coupling relationship with the antenna assembly on the stationary device throughout each complete revolution of the rotating device. Thus, data can be reliably sent and received at a relatively fast data rate, e.g., approximately 10 megabits per second, over each channel substantially independent of the position of the rotating device.

The invention is useful whenever information must be transferred between a rotating system and a stationary system, such as a CT scanner, where control and information data can advantageously be transferred in real time.

The invention will be more fully understood from the following detailed description, in conjunction with the accompanying figures, wherein:

FIG. 1 is a block diagram of a prior art ETHERNET communications network;

FIG. 2 is a schematic diagram of a mechanically non-contacting communications system of the present invention;

FIG. 3 is a schematic cross-sectional view of a second device rotatably disposed within a first device and utilizing the communication system of the present invention;

FIG. 4 is a more detailed schematic cross-sectional view of the rotatable device having an antenna assembly disposed about its periphery and rotatable within an aperture of a stationary device having a stationary antenna disposed therein;

FIG. 4A is a schematic side view depicting a rotating set of micro-strip conductors disposed about the circumference of the rotatable device of the apparatus shown in FIG. 4;

FIG. 4B is a schematic side view depicting a stationary set of micro-strip conductors fixed relative to the stationary device and capacitively coupled to the conductors of the rotating device;

FIG. 5 is a cross-sectional view of the normal operating position of four rotating micro-strip conductors cooperative with two stationary micro-strip conductors, and their associated ground planes;

FIGS. 5A, 5B, 5C, and 5D are cross-sectional views of four operating position extreme of the rotating micro-strip conductors relative to the stationary micro-strip conductors of FIG. 5;

FIG. 6 is a block diagram of two RF receivers and an RF transmitter cooperative with a stationary antenna assembly and a stationary ETHERNET communications board;

FIG. 7 is a block diagram of an RF receiver and two RF transmitters cooperative with a rotating antenna assembly and a rotating ETHERNET communications board; and

FIG. 8 is an end view of a CT scanner modified to include the present invention.

With reference to FIG. 1, it is known to transmit serial data at high speed over coaxial cable 10 using various protocols and encoding techniques. Each node at which data is transmitted and/or received on the cable is provided with a transceiver, such as indicated at 12 and 14. One commonly used protocol is ETHERNET. An ETHERNET transceiver preferably uses standard encoding techniques, such as Manchester encoding, of a digital signal at a relatively high bit rate, for example, 10 megabits per second. The receiver portion of the ETHERNET transceiver recovers the clock signal from the serial data, then extracts the serial data.

According to the present invention, a protocol is used that is self-timing and is capable of being transmitted at relatively high data rates. In a preferred embodiment of the present invention, the ETHERNET ISO/IEC 8802.3 standard, similar to the IEEE 802.2 standard, has been chosen because of these requirements and, in part, because it is well-known, and as such easily adapted to the present invention. It should be appreciated that other protocols and encoding techniques may be employed depending upon the particular application in which the invention is to be used.

Referring to FIG. 2, the invention includes a non-contacting (i.e., in the mechanical sense) communications link having an encoder-transmitter 15 and a receiver-decoder 16 cooperating respectively to transmit and receive data across a spatial gap. The link of FIG. 2 can be implemented using any mechanically non-contacting communications technique, such as an optical or radio frequency technique, including infrared, ultraviolet, or any other useful frequency range of the electromagnetic spectrum. Moreover, capacitive or inductive coupling can be utilized. In a preferred embodiment of the invention, radio frequency (RF) capacitive coupling is employed. In an alternate preferred embodiment, near field transmission is employed, using a near field antenna assembly.

In a further preferred embodiment of the invention, the encoder-transmitter 15 includes an encoder, such as an ETHERNET transceiver 17 configured to transmit only, for providing an encoded digital signal 20 representative of a digital input data signal 18 in accordance with ETHERNET protocol. A transmitter, such as a radio frequency (RF) transmitter 22, receives the encoded digital signal 20 from transceiver 17, and provides an analog RF signal 23, representative of the encoded signal 20, to transmitting antenna assembly 24 of the encoder-transmitter. The receiver-decoder includes a receiving antenna assembly 26, disposed at a distance from the transmitting antenna assembly 24, for detecting the analog RF signal 27, and providing it to an RF receiver 28 of the receiver-decoder. The RF receiver 28 provides a digital encoded signal 29, to an ETHERNET transceiver 30 of the receiver-decoder, transceiver 30 being configured to receive only. The ETHERNET transceiver 30 then decodes the encoded signal 29, thereby providing a digital output data signal 32 that is the same as the digital input data signal 18 in terms of its information content.

FIG. 3 shows, schematically and in cross-section, a first device 34 having an opening 36 for receiving a second device 44. The first device is preferably stationary with respect to a supporting surface 39. A stationary transceiver assembly 37 is fixed relative to the first device 34. The second device 44 is supported within the opening 36 so that it is rotatable about a rotation axis (normal to the view plane of FIG. 3) and forms within the opening 36 an annular air gap, indicated at 40; between the outer periphery 35 of the rotatable device 44 and the inner circumference 43 of the opening 36. A rotatable transceiver 41 is fixed relative to and rotates with the second device 44.

In a preferred embodiment, it is desirable that more information (approximately twice as much) be transmitted from the rotatable device 44 to the stationary device 34 than transmitted from device 34 to device 44 so that the transceiver assembly 37 of the first device 34 includes two receivers for simultaneously receiving two data signals, and only one transmitter for transmitting one data signal. The rotatable device 44 preferably includes a second ETHERNET transceiver assembly 41 that is complementary to the first transceiver assembly 37 in that, for each transmitter of the first transceiver assembly 37 there is a respective receiver in the second transceiver assembly 41, and for each receiver of the first transceiver assembly 37 there is a respective transmitter in the second transceiver assembly 41. Preferably, each receiver of transceiver assemblies 37 and 41 includes an RF receiver 28 as shown in FIG. 2 that receives an RF signal 27 and provides an encoded digital signal 29, and an ETHERNET receiver 30 that receives the encoded digital signal 29 and provides a decoded digital data signal 32. Similarly, each transmitter of the transceiver assemblies 37 and 41 includes an ETHERNET transmitter 17 that receives a digital data signal 18, such as a digital data signal from a computer, and provides an encoded digital signal 20 and an RF transmitter that transmits an RF signal 23 representing the encoded digital signal 20.

As will be more evident hereinafter, each transmitter and receiver of the rotatable transceiver assembly 41 includes an antenna assembly, generally disposed around the periphery 35 of the rotating device and terminating in its characteristic impedance at 42, preferably 180.degree. opposite where the corresponding transmitter or receiver is connected. An antenna assembly for each of the transmitter and receivers of the transceiver assembly 37 is fixed relative to stationary device 34 within the air gap 36 at a fixed distance from the corresponding antenna assembly on periphery 35 of the rotating device 44 (so that the spacing between the two antenna assemblies remains substantailly constant as the rotating device 44 rotates) and also terminates at each end with its characteristic impedance. The stationary antenna assembly extends around the periphery of rotating antenna through a predetermined arc sufficiently large so that as the terminated ends of the antenna 35 at 42 rotate past the stationary antenna assembly, data can still be transferred between the two assemblies so that data transfer can occur at any angular position of the rotatable device 44.

Thus, in the present embodiment, data is communicated through air gap 36 from the transmitter of the transceiver assembly 37 of stationary device 34 to the receiver of transceiver assembly 41 of the rotatable device 44 using one transmitter/receiver pair, and data is communicated from the two transmitters of assembly 41 of rotatable device 44 to the corresponding receivers of the assembly 37 of the stationary device 34 using two transmitter/receiver pairs. Therefore, as the terms are used herein, there are two "down link" channels and one "up link" channel. Consequently, in a preferred embodiment, data can be transferred from the rotatable device 44 to the stationary device 34 at twice the rate that data can be transferred to the rotatable device 44 from the stationary device 34. This embodiment is especially useful when a computer system is affixed to the rotating device 44 for extensive data acquisition, such as image data acquisition system of a CT scanner, and must transmit the image data to a stationary computer system fixed relative to supporting surface 39, and the stationary computer provides a lesser amount of control and system diagnostic data to the rotating computer system.

As shown in greater detail in FIGS. 4, 4A and 4B, preferably, stationary antenna assembly 46 for the stationary device 43 is provided in the form of a set of micro-strip conductors 60, 62, 64, 66 and 68 (seen schematically in FIG. 4B) electrically connected to the stationary transceiver assembly 37, while a rotatable antenna assembly 35 for the rotatable device 44 is provided in the form of a set of micro-strip conductors 50, 52, 54, 56 and 58 (seen schematically in FIG. 4A) electrically connected to rotatable transceiver assembly 41. The micro-strips 60, 62, 64, 66 and 68 of the stationary antenna assembly 46 are fixed relative to the surface 43 forming the outer surface of air gap 40 so as to be precisely spaced from the rotatable micro-strip conductors of assembly 48 as the rotatable device rotates about its axis. The stationary micro-strip conductors 60, 62, 64, 66 and 68 of antenna assembly 46 are each connected to the transceiver 37 so as to form a two pole antenna (i.e., the transceiver is connected to the center of each strip 60, 62 and 64), and each are of a length (from end to end) that is less than one quarter of the wavelength of the highest transmission frequency of any signal transmitted to or received from the rotating device 44 so that coupling between the two antenna assemblies is capacitive. For example, when the highest frequency transmitted is about 480 MHz, the end-to-end length of each micro-strip conductor 60, 62 and 64 of assembly 46 is no more than about 300 mm, although smaller lengths are preferred. The fixed micro-strip conductors 60, 62, 64, 66 and 68 of antenna assembly 46 preferably lie on a curved surface which preferably has a center of curvature coincident with the rotation axis of the rotatable device so as to lie along an arc which extends coincident with and preferably lies within the air gap 40 so that the distance between the micro-strip conductors of the stationary antenna assembly and the micro-strip conductors of the rotatable antenna assembly is substantially constant around the entire circumference of the stationary antenna assembly.

In a preferred embodiment, the micro-strip conductors 60, 62, 64, 66 and 68 of stationary antenna assembly 46 are realized as conductive traces on a printed circuit board, while the rotating micro-strip conductors 50, 52, 54, 56 and 58 of rotatable assembly 48 are disposed on a flexible ribbon.

As will be apparent hereinafter, the micro-strip conductors 60, 62, 64 are each provided as a set of two strips, while micro-strip conductors 50, 52 and 54 are each provided as a group of four strips, with each set and group being differentially driven, while micro-strip conductors 66, 68, and 56 and 58 are grounded. All of the micro-strip conductors are active transmission lines disposed over a continuous ground plane, the transmission lines having a characteristic impedance of, for example, 50 ohms.

The micro-strip conductors 50, 52, 54, 56 and 58 of assembly 46 of the rotatable device 44 are circumferentially arranged around both sides of the periphery 35 of the rotatable device 44 from the location of the transceiver assembly 41 and terminating 180.degree. therefrom as indicated at 42. Thus, half of each of the rotating micro-strip conductors 50, 52, 54, 56 and 58 of antenna assembly 48 are disposed along a first half of the outer periphery 35 of the rotatable device 44, and the remaining half of each of the rotating micro-strip conductors are disposed along a second half of the outer periphery 35 of the rotatable device 44, ensuring that the signal strength transmitted between the two assemblies 46 and 48 remains substantially constant throughout a complete revolution of the rotating device 44.

In applications where extremely low error rates are required, such as medical diagnostic equipment, e.g., CT scan apparatus, cross talk between data channels must be minimized. Referring to FIG. 4A, the three pairs of conductors 60, 62 and 64, are used with a corresponding group 50, 52 and 54 so as to define three separate data transmission channels. To reduce cross talk between the channels, the conductor groups 50 and 52 are separated by a first grounded guard conductor 56, and the conductor groups 52 and 54 are separated by a second grounded guard conductor 58. Similarly, the conductor pairs 60 and 62 are separated by a grounded guard conductor 66, and the conductor pairs 62 and 64 are separated by a grounded guard conductor 68.

To further reduce cross talk, the groups 50 and 54, used for transmitting signals respectively to the conductor pairs 60 and 64 so as to define the two down-link channels, are driven at one or more drive frequencies within a first frequency range f.sub.1, and the conductor pair 62 used for transmitting signals to the group 52 so as to define the up link channel, are driven at one or more drive frequencies within a second frequency range f.sub.2 which is outside of, and preferably less than the frequency range f.sub.1. Disposing the conductor group 52 of the up link channel between the conductor groups 50 and 54 of the respective down link channels further reduces cross talk by increasing the spatial separation between lines driven at the same frequency, thereby exploiting the FM capture effect. Thus, for example, the frequency range f.sub.1 can fall generally within the range of 130-230 MHz, and the range f.sub.2 can fall generally within the range of 320-470 MHz. The driving frequencies of the second frequency range f.sub.2 are preferably chosen so as to be coincident with null frequencies associated with the first frequency range f.sub.1, thereby further reducing cross talk, where the null frequencies associated with the first frequency range depend on the first frequency range f.sub.1, and the range f.sub.1 is chosen so as to provide a null spacing that is substantially coincident with the spacing of the conductors within a strip line cable that includes the pairs 50, 52, and 54.

In a preferred embodiment, data transmitted over the two down link channels is packetized in accordance with the ETHERNET protocol identified above, so that each packet includes addressing information. Thus, even if cross talk occurs between the two down link channels, data can be delivered to its intended address.

Having two down link channels, data can be sometimes carried simultaneously over the two down link channels, and sometimes alternately carried over one down link channel or the other down link channel. In order to further minimize cross talk, the two down link channels preferably are time-multiplexed such that the amount of time that data is simultaneously carried over the two down link channels is small relative to the time that data is alternately carried over one down link channel or the other down link channel. For example, the percent of time that data is simultaneously carried over the two down link channels is advantageously only about one percent. Preferably, only synchronization data is transmitted during the period of channel transmission overlap, while other critical data, such as image data, is transmitted only when a single channel is active.

To minimize radiative losses, the four conductors of each of the outer groups of micro-strip conductors 50 and 54 are differentially driven in pairs (++--), i.e., a first pair of the four conductors (the + conductors of each pair 50 and 54) is driven in opposite phase with respect to a second pair of the four conductors (the - conductors of each pair 50 and 54). Preferably, to obtain better than 20 dB rejection from symmetry, the amplitude of the oppositely phased signals must be equal to within about 5%. Additionally, in a preferred embodiment, to further reduce radiated power, the transmitter power is limited to about 20 mW or less (e.g., 1 V RMS 50 ohm).

In a manner well known in the art, a balun transformer (not shown) is used to drive each of the conductors 50, 54 and 62 when transmitting a signal through the respective transmitting channel so as to match the impedance of the conductors to the impedance of the transmitter of the respective transceiver that drives them, thereby enhancing power transfer between the transmitter and the receiving conductors. The receiving conductors 52, 60 and 64 are driven by oppositely phased RF signals provided from the transmitting conductors 62, 50 and 54, respectively. These receiving conductors are also connected through a balun transformer (not shown) to the respective receiver of the corresponding transceiver.

With reference to FIG. 4B, the stationary groups of micro-strip conductors 60, 62 and 64 of the antenna assembly 46 are cooperative with the respective rotating set of micro-strip conductors 50, 52 and 54 of the antenna assembly 48. The assembly 46 includes three groups of conductors 60, 62, and 64, disposed close enough to the respective rotating micro-strip conductors 50, 52 and 54 of the assembly 48 to ensure good electrical coupling thereto, and far enough to accommodate mechanical tolerances of the rotating device 44 and the stationary device 34 so that the two never mechanically contact one anther. Further, each of the micro-strip conductors is sufficiently wide so as to maintain coupling throughout rotation of the rotatable device 44 and during out of plane motion (e.g., nutation) of the rotatable device 44.

Referring to FIGS. 4B and 5, it is seen that each of the differential pair of the conductor groups 50, 52 and 54 is actually formed as a loop so that, for example, the + pair of conductors of group 50, includes + strips 68 and 70 connected at their ends through their characteristic impedances at termination point 42 to ground. The corresponding pair of conductors 60, 62 and 64 (60 being shown in FIG. 5) is provided as one + strip 66 and one - strip 72, respectively disposed between and spaced from strips 68 and 70 and from strips 74 and 76. In a normal position strips 66 and 72 of each of the differential pairs of conductor groups 50, 52 and 54 are radially spaced from strips 68, 70, 74 and 76 of each of the pairs of conductors 60, 62 and 64 by a predetermined amount, e.g., 1.5 mm, so as to provide capacitive coupling with good RF transmission and reception at the various driving frequencies and power levels of the transmitted signals. In the preferred embodiment, the ground conductor 78 is incorporated into the printed circuit board supporting conductors 60, 62 and 64, while the ground plane conductor 80 is incorporated into the flexible ribbon supporting conductors 50, 52 and 54, wherein a layer of insulation separates the micro-strip conductors from the corresponding ground plane conductor. The ground planes 78 and 80 provide electromagnetic shielding.

Although the dimensions of the micro-strip conductors can vary depending upon the particular application, in the preferred embodiment, the length of each of the micro-strip conductors 50, 52, 54, 56 and 58 is about 2 meters. The width of the micro-strip conductors 50, 52, 54, 56 and 58 are about 1.57 mm, while micro-strip conductors 60, 62, 64, 66 and 68 are about 2.5 mm wide. While the radial separation between the stationary and rotating micro-strip conductors in the preferred embodiment is 1.5 mm, the spacing can vary from about 0.5 mm to about 2.5 mm as the device 44 rotates about its axis, without degrading signal transmission between the stationary and rotating devices 34 and 44. Similarly, the rotating device 44 can laterally move out of its rotation plane with respect to the stationary device 34 by about .+-.1.0 mm.

FIGS. 5A, 5B, 5C, and 5D each represent a different combination of radial and lateral out of plane displacement, showing how proximity can vary, for example, from about 0.5 mm to about 2.5 mm, as can be seen by comparing FIG. 5A with FIG. 5C, or FIG. 5B with FIG. 5D, while at the same time, lateral out of plane displacement can vary, for example, by about 1.0 mm, as can be seen by comparing FIG. 5A with FIG. 5B, or FIG. 5C with FIG. 5D.

FIG. 6 shows in detail the stationary transceiver assembly 37 of FIG. 4, including a transmitter and two receivers. More specifically, a stationary computer 81 is connected to an ETHERNET communications board 82 that includes an ETHERNET transceiver 84 set to transmit, and two ETHERNET transceivers 86 and 88 set to receive. The stationary antenna assembly 90 includes the stationary set of micro-strip conductors 46 (of FIG. 4B), as previously described. An RF transmitter 92 is responsive to an ETHERNET level encoded data signal 94 provided from the transmitter 84, and provides a frequency shift key (FSK) RF signal 96 representative of the signal 94 to the stationary antenna assembly 90. In alternate embodiments, other modulation techniques can be used, such as phase modulation and spread spectrum modulation.

The RF transmitter 92 includes an RF switch driver 97 which provides two output driving signals 100 and 102 which are always inverted with respect to one another. When the ETHERNET level encoded data signal 94 is in a high state, for example, driving signal 100 is high while driving signal 102 is low. Conversely, when signal 94 is in a low state driving signal 100 is low while driving signal 102 is high.

For example, the ETHERNET signal can transition between 0 and -2 volts at 10 megabits a second, while the driving signals 260 and 264, and 262 and 266 transition between 0 and -5 volts. The two signals 100 and 102 are used to respectively drive two RF switches, such as a Gallium Arsenide RF switches, of a RF switch module 98. The switches are designed to close when the state of the respective drive signal is of a certain state, such as high so that one of the switches is always closed and one always open depending upon the state of the ETHERNET level encoded data signal 94. Two filtered and amplified signals 112 and 114 each of a different frequency are applied to each of the switches of switching module 98, so that the FSK signal 104 provided at the output of switch 98 is of one frequency when the ETHERNET level encoded data signal 94 is of one state (high) and is of a different frequency when signal 94 is of an opposite state (low). In order to generate the FSK signal 104 at the two frequencies, two separate oscillators are provided, one the HI oscillator 116, set at a high frequency, the other the LO oscillator 126, set at a lower frequency.

In a preferred embodiment, the HI oscillator 116 is a standard TTL oscillator that provides a plurality of harmonics, where the third harmonic is a 210 MHz signal 118 that is selected by a bandpass filter 120. A filtered signal 122 provided by the filter 120 is amplified by a buffer amplifier 124 that isolates the oscillator 116 from the RF switch 98 so as to produce drive signal 112 that is applied to RF switch 98. The LO oscillator 126 is also preferably a standard TTL oscillator that provides a signal 128 having a plurality of harmonics including a third harmonic signal 132 at 138 MHz, which is selected by a bandpass filter 130. The filtered signal 132 is amplified by a buffer amplifier 134 that isolates the oscillator 126 from the RF switch 98 so as to provide drive signal 114 that is applied to RF switch module 98. The RF switch module 98 provides an FSK signal 104 to an output amplifier 106 so as to produce an amplified FSK signal 108 to a 270 MHz low pass filter 110. The filter 110 provides a filtered and amplified FSK RF signal 96 to the stationary antenna assembly 90 for transmission. Signal 90 is preferably about 20 milliwatts; although this can clearly vary depending upon the design of the antenna assemblies and the dimensions of the air gap 40.

FIG. 6 also shows two RF receivers 136 and 138. The stationary antenna assembly 90 provides FSK RF signals 140 and 142, each of which, as will be more evident hereinafter, contains two frequency components, respectively representative of the high and law states of the ETHERNET level encoded signal and well above 290 MHz. The FSK RF signals are applied respectively to high pass filters 144 and 146 (290 MHz) which remove cross-talk from the up link signal provided on the up link channel. Filtered signals 147 and 149 are respectively provided from the outputs of filters 144 and 146 and applied to the corresponding RF amplifiers 148 and 150 each having, for example, 52 dB gain. The amplified signals 152 and 154 are provided to corresponding delay lines 156 and 158 and to phase detectors 160 and 162. The outputs of lines 156 and 158, delayed signals 164 and 166 are also provided to the respective phase detectors 160 and 162. The phase detectors 160 and 162 cooperate with the corresponding delay lines 156 and 158 so as to FSK demodulate the corresponding signals 152 and 154. The delay lines 156 and 158 are chosen according to the lower frequency of the pair of FSK frequencies of each signal, so the phase difference will be 0 degrees at the lower frequency and therefore the output of the detector will be at its most negative voltage level (a logic low signal). At the higher frequency, the phase difference will be 180 degrees, and the output of the detector will be at its most positive (a logic high signal). Alternatively, the phase detectors 160 and 162 each provide a negative voltage when its two input signals are in phase, and a positive voltage when they are out of phase. Thus, the demodulated signals 168 and 170 represent data as a sequence of high and low states which represent the sequence of frequency shifts of the amplified FSK signals 152 and 154 which in turn represent the original ETHERNET level encoded data signals received by the assembly 90. The demodulated signals 168 and 170 are then respectively provided to low pass filters 172 and 174 (e.g., 30 MHz), resulting in filtered signals 176 and 178 being provided to the corresponding comparators 180 and 182 and to threshold control modules 184 and 186, wherein each comparator cooperates with a threshold control module to normalize signal amplitude, rebalance the signal duty cycle, and correct DC signal offset, while preserving the information represented by the respective signals 176 and 178 so as to provide corrected signals 188 and 190 to the corresponding ETHERNET drivers 192 and 194. The ETHERNET drivers 192 and 194 respectively provide ETHERNET level signals 196 and 198 to the corresponding receivers 86 and 88 on the stationary ETHERNET communications board 82 for use by, for example, the stationary computer 81. Although the signals 140 and 142 may exhibit substantial phase jitter, by processing them in the manner just described such phase jitter is significantly reduced in the signals 196 and 198 that are received by the stationary ETHERNET communications board 82.

Referring to FIG. 7, the rotating transceiver assembly 41 is described in greater detail. RF signals are communicated between the stationary antenna assembly 90 (not shown in FIG. 7) and the rotating antenna assembly 200 so that an FSK RF signal 202 (essentially signal 96 of FIG. 6 transmitted by the antenna assembly 90) is received by the rotating antenna assembly 200, and converted into an ETHERNET level signal 206 by an RF receiver 204 for use by an ETHERNET receiver 208 on a rotating ETHERNET communications board 210. Conversion of the FSK RF signal 202 into the ETHERNET level signal 206 is accomplished in essentially the same manner as in the RF receivers 136 and 138 of FIG. 6.

More specifically, rotating antenna assembly 200 provides an FSK RF signal 202 which contains two frequency components, respectively representation of the high and low states of the ETHERNET signals and well above 290 MHZ. The FSK RF signals are applied respectively to a low pass filter (e.g., 270 MHZ) 212 which removes cross-talk from the down link signals provided over the down link channels. The filtered signal 214 is applied to an RF amplifier 216 having, for example, 60 dB gain. The amplified signal 218 is provided to a delay line 220 and to a phase detector 222, wherein a delayed signal 224 at the output of the delay line 220 is also provided to the phase detector 222. The phase detector 222 cooperates with the delay line 220 so as to FSK demodulate the amplified signal 218. For example, the phase detector 204 provides a negative voltage (logic low state) when its two input signals 222 and 224 are in phase with each other, and a positive voltage (logic high state) when they are out of phase. Thus, the demodulated signal 226 represents data as a sequence of two voltage levels (high and low states) which represents the sequence of frequency shifts of the amplified FSK signal 218 (as well as the original ETHERNET level encoded data signal 94 shown in FIG. 6). The demodulated signal 226 is then provided to a low pass filter 228 (e.g., 30 MHz), resulting in filtered signal 230 being provided to a comparator 232 and to a threshold control module 234, wherein the comparator 232 cooperates with the threshold control module 234 to normalize signal amplitude, rebalance the signal duty cycle, and correct DC signal offset, while preserving the information represented by signal 230 so as to provide a corrected signal 236 to an ETHERNET driver 238. The ETHERNET driver 238 provides an ETHERNET level signal 206 to the receiver 208 on the rotating ETHERNET communications board 210 for use by, for example, the rotating computer 240. Although the signal 202 may exhibit substantial phase jitter, such phase jitter is significantly reduced by the signal processing described above, before being applied to the rotating ETHERNET communications board 210.

A two-channel RF transmitter 242 is responsive to two ETHERNET level encoded data signals 244 and 246 provided by two transmitters 248 and 250 of the rotating ETHERNET communications board 210. The RF transmitter 242 provides two frequency shift key (FSK) RF signals 284 and 286, representative respectively of the signals 244 and 246, to the rotating antenna assembly 200.

The RF transmitter 242 includes two RF switch drivers 252 and 254 that drive RF switch modules 256 and 258, respectively. The modules 256 and 258 each include two RF switches, wherein the first switch is responsive to the corresponding first driving signals 260 and 262, and the second switch is responsive to the corresponding second driving signals 264 and 266 that are inverted with respect to the first driving signals 260 and 262 such that when one switch of an RF switch is open, the other switch of the RF switch is closed. For example, the ETHERNET signal 244 is a 10 MHZ signal that transitions between a 0 volts and -2 volts, and the driving signals 260 and 264 transition between 0 and -5 volts.

The RF switch modules 256 and 258 respectively provide FSK signals 268 and 270 to the corresponding output amplifiers 272 and 274 so that the amplifiers provide amplified FSK signals 276 and 278 to the 290 MHZ low pass filters 280 and 282 respectively. The filters 280 and 282 provide filtered and amplified FSK RF signals 284 and 286 to the rotating antenna assembly 200. Preferably, the signals 284 and 286 applied to antenna assembly 200 are each about 20 milliwatts; although this can clearly vary depending upon the design of the antenna assembly and the dimensions of the air gap 40.

The RF switch modules 256 and 258 respectively receive two filtered and amplified oscillator signals 288, 290 and 292, 294. In a preferred embodiment, a PLL UHF transmitter chip, such as the MOTOROLA 3240 transmitter chip, is used to generate two oscillators signals in the ultra high frequency (UHF) range, thereby serving as a HI oscillator 296 and a LO oscillator 306. The HI oscillator 296 provides a 480 MHZ signal 298 to a buffer amplifier 300 that isolates the oscillator 296 from the RF switches 256 and 258. A buffer amplified signal 302 provided by the buffer amplifier 300 is split by a splitter 304 into the two signals 290 and 294, which in turn are applied to the corresponding switches 256 and 258.

The LO oscillator 306 provides a 320 MHZ signal 308 to a buffer amplifier 310 that isolates the oscillator 306 from the RF switches 256 and 258. A buffer amplified signal 312 provided by the buffer amplifier 310 is split by a splitter 314 into the two signals 288 and 292 which in turn are provided to switches 256 and 258, respectively.

In a preferred embodiment, to further reduce jitter, the oscillators 296 and 306 receive timing information from the rotating computer 240, and the oscillators 116 and 126 receive timing information from the stationary computer 81.

The preferred embodiment of each of the transmitters 92 and 242 is characterized as having an input signal provided by an ETHERNET transmitter in accordance with Standard ISO/IEC8802-3 (ethernet) P.L. (10 Base 5). The transmitters have an output signal of 7 dBm.+-.3 dBm. Power consumption is less than 2.5 Watts per channel using a +12 v line. Jitter introduced by a transmitter is less than 8 nanoseconds. In addition, the preferred receivers 136, 138, and 204, each is characterized as having an input signal in the range of -10 dBm to -50 dBm, and an output signal in accordance with ISO/IEC 8802-3 (ethernet) P.L. Power consumption is less than 2.5 Watts per channel using a +12 volt line. Jitter introduced by a receiver is less than 6 nanoseconds.

To further illustrate a possible use of the apparatus of the invention, in FIG. 8 a typical CT scanner has been modified to include the present invention. As shown, a drum 320 is rotatably supported in a gantry frame 322 for rotation about an axis 324. A source 326 of X-rays and a detector array 328 are disposed on opposite sides of an opening 329 adapted to receive the object to be scanned. A data acquisition system 330 is also provided on the drum 320 for acquiring image data provided by detectors of array 328 during a scan. An on board computer 240 is mounted on the drum. The gantry frame 322 is supported in a yoke 332 which is also used to support the stationary computer 81.

In accordance with the present invention, the rotating antenna assembly 200, is preferably mounted around the perimeter of the drum in a manner as previously described. The ETHERNET communications board 210, RF receiver 204 and RF transmitters 242 are suitably mounted on the drum, (as generally indicated at 334 in FIG. 8) and connected to computer 240 and antenna assembly 200 in the same way as described in FIG. 7. The stationary antenna assembly 90 is secured to the frame in proximity to the rotating antenna assembly 200, as previously described in connection with FIG. 6. The ETHERNET communication board 82, RF receivers 136 and 138, and the RF transmitter 92 are suitably fixed relative to the yoke, as generally indicated at 336, in FIG. 8, and connected to computer 81.

Upon receiving control data, the detector array 326 provides data to the data acquisition system 330. The data is provided to rotating computer 240. In addition, other data associated with the lateral movement of the drum within the rotational plane of the drum, can also be sensed by detectors (not shown) and compensation data can be generated along with the imaging data. Such a system is shown and described in U.S. patent application Ser. No. 08/162,653, entitled APPARATUS FOR AND METHOD OF MEASURING GEOMETRIC, POSITIONAL AND KINEMATIC PARAMETERS OF A ROTATING DEVICE filed in the names of Bernard M. Gordon, Douglas Abraham, David Winston and Paul Wagoner on Dec. 6, 1993 and incorporated herein by reference, which was abandoned in favor of continuing U.S. patent application Ser. No. 08/338,263 filed Nov. 10, 1994 and issuing as U.S. Pat. No. 5,432,339 on Jul. 11, 1995, entitled "Apparatus For and Method of Measuring Geometric, Positional and Kinematic Parameters of a Rotating Device Having a Plurality of Interval Markers". The movement compensation data is used to compensate for variations, vibrations, and imperfections in the rotational motion of the rotating device 44 so as to provide image data of a quality that more closely approximates image data collected by a geometrically perfect and rotationally stable rotating device. After data acquisition, data collected from the detector array is merged with compensation data, the merged data then being transmitted via the two time-multiplexed down-link channels.

Thus, measurement and control data is transmitted from the drum 320 to the stationary computer 81 via the two time-multiplexed down-link channels so as to provide high speed data transfer. It is necessary to employ two down link channels when data is generated or acquired at a rate that exceeds the capacity of a single channel, such as in some CT scan applications. In the preferred embodiment, the data rate of a single channel is determined by the capacity of an ETHERNET transceiver, which is 10 megabits per second in the presently described embodiment.

The computer 81 checks the merged data for integrity upon its receipt. The measurement data is then extracted from the merged data for further processing. In a CAT scan system, for example, the measurement data is used in a back projection process.

To further illustrate the apparatus of the invention, the stationary computer 81 generates control information at a rate of 0.1 Mbyte per second represented by, for example, a sequence of 64-byte data blocks every 700 microseconds, and this control information is transmitted by the transmitter 84 on the stationary ETHERNET communications board 82 to the RF transmitter 92 and stationary antenna assembly 90 for reception by the rotating antenna assembly 200, the RF receiver 204, and the ETHERNET receiver 208, for use by the rotating computer 240 on the rotating device 40. The control information thus transmitted and received is generated and used in real-time. Upon receipt of a data block, data is acquired by a data acquisition system (not shown) on board the rotating device 40, and the information conveyed by the data block is used to control other subsystems (not shown) on board the rotating device 40.

The data acquisition system on board the rotating device 40 generates data for transmission to the stationary device at a rate of approximately 1.2 Mbytes per second as a sequence of 800-byte data blocks every 700 microseconds.

Other modifications and implementations will occur to those skilled in the art without departing from the spirit and the scope of the invention as claimed. For example, the data communication systems described can be easily implemented for transferring data between two devices which move relative to one another, but not necessarily rotationally about a rotation axis. For example, a device, such as a train, that moves over a linear track can be provided with a transcesiver assembly 37 and an antenna assembly similar to assembly 46 except flatten so as to travel in a plane parallel to the plane of the track, and the track provided with the transceiver 42 and the antenna assembly similar to assembly 48, except flattened to follow the track. Accordingly, the above description is not intended to limit the invention except as indicated in the following claims.