TGPU Theory

The Ethernet Controller chip controls the 10Base-T connection with the console.

The TGPU has three CAN channels, and CAN1 is used for Gantry cover Push Buttons and Displays. CAN3 is used for connection to the Global table. CAN2 is used for the axial servo motor.

LSCOM is the communication way between TGP and ORP via slip rings. It uses three signals: SER_SREF (reference signal), SER_OUTBOUND (transmit signal), and SER_INBOUND (receive signal). The LSCOM interface needs an isolated +/- 5Vdc bipolar power supply to power the driver/receiver circuits. In addition, optical isolation is maintained between the slip rings and the ORP logic circuits.

The TGP board outputs EXP_ENBL signal to the ORP board via a slip ring for interrupting EXPCMD signal to JEDI.

This is a steady-state +24Vdc input signal from the Gantry to close the "X-Ray ON" Light relay. The x-ray interlock is passed through a relay on the TGPU. To close the relay, the watchdog circuit must be active and the relay must be commanded to close via TGP processor. The TGPU board will provide a set of 24v/40mA contacts to control a 24v relay in the PDU. The 24v PDU relay will close a set of 110VAC contacts that drive the hospital X-ray On Light. The 24v relay contacts will be closed (x-ray light turned on) whenever the TGPU board commands x-rays to the ORP. A register written to by firmware will command the x-ray on light’s relay. The bits of the register will be cleared in the event of a power failure, CPU fault, or watchdog / board fault condition.

Steady-state +24Vdc input signal from the Gantry to close the "System ON" Light relay. NGPDU provides isolated terminals for customer Room Light connections.

Steady-state +24Vdc input signal from the Gantry to close the "Generator Ready" Light relay. NGPDU provides isolated terminals for customer Room Light connections.

Two signals are provided for use with defined cardiac features: Exposure Command and R-Pulse. Exposure command is the same signal as the command of the same name described in the Scan Control section of this document, however it is also provided to the TGPU as a 422 signal for transmission to the board providing isolation for the EKG machine. R-Pulse is a signal, received from the Gantry Options board providing isolation for the EKG machine, which indicates that the heart is in a particular part of the cardiac cycle. The status of the R-Pulse signal and a mask able positive edge sensitive interrupt can be read back by the TGP via registers on the TGPU.

Two signals are provided for use with defined pulmonary features: Resp_mon and Resp-Pulse. Resp-Pulse is a signal, received from the Gantry Option board providing isolation for the pulmonary monitor, which indicates that the lungs are in a particular part of the volumetric capacity. The status of the Resp-Pulse signal and a mask able positive edge sensitive interrupt can be read back by the TGP via registers on the TGPU.

Smartview Footswitch : A footswitch is used by the operator to control scanning during a Smartview procedure. The footswitch consists of two switches, one normally open, and one normally closed, which each change state when the footswitch is pressed.

Smartview Hand Held Control: A hand held control is used by the operator to control scanning and table motion during a Smartview procedure. The hand held control consists of a RX/TX signal is controlled by the TGPU.

Signals from the axial encoder and azimuth detection board measure the gantry position. The gantry position is used to monitor axial drive positioning, velocity performance and to determine starting x-ray and view angles

Gantry Position is measured with an incremental encoder mounted on the gantry's motor drive shaft. The motor and encoder turn 13 times for every one gantry revolution. The encoder has two channels, A and B, in quadrature with a resolution of 2,048 pulses per channel per encoder revolution. There are (2,048 X 13) = 26,624 Ch. A and Ch. B encoder pulses per gantry revolution. Channel A and B taken in quadrature provide a 106,496 pulse per gantry revolution resolution. Encoder accuracy of 0.0135 degrees per channel pulse, or 0.00338 degrees per quadrature pulse. The TGPU provides a filtered +5v and ground to the axial drive motor encoder. This power is filtered to prevent tube spit noise from propagating in through the encoder cable and corrupting the TGPU.

The home position is the gantry position with the x-ray tube positioned at 12 o'clock. This position is sensed using an optical home flag and home flag sensor board. The home flag is a 1 inch wide piece of metal attached to the rotating bearing. The TGPU board supplies +5v to the home flag board. The home flag is used on the TGPU board in conjunction with the axial encoder “C” pulse to determine gantry home position for firmware.

The status of the axial drive enable switch can be read back by the TGPU. While the axial drive switch is in the disabled position, the axial drive enable output is forced inactive and the axial holding brake output is forced to release the brake.

The axial holding brake, which is normally applied, is released by applying 120VAC to the brake leads. The 120 VAC is controlled by a solid state relay that in turn is controlled by the TGPU. Note that the TGPU axial brake output is forced to release the brake when the axial drive enable switch is in the disabled position. The axial brake is meant as a static brake to hold the gantry still once it has been positioned by the axial drive. The brake's friction is not sufficient to hold the gantry still against the full accelerating force of the motor and amplifier. Should the brake fail while the gantry is in motion, the gantry will continue to rotate until halted by firmware. The brake is also not sufficient to hold the gantry while the tube or inverters are being changed. Whenever servicing the rotating base, the gantry should be locked out using the locking pin mechanism. The axial brake is released when the Gantry Loop Contactor Service Switch is in the "disable" position. This allows the gantry to be rotated by hand without fighting the friction of the brake.

The axial motor drive is powered by two sources: The main source of power is from three phase 480VAC controlled by the axial power contactor. The second source of power is provided via the drive’s DC bus by the axial dynamic brake. The axial power control relay, axial drive enable switch and drives power must all be active for the axial power contactor to close.

The 480VAC axial power contactor can be read back when a maskable change of state interrupt occurs on the TGPU processor.

The axial drive is commanded by the firmware via CAN network. There are seven signals that are used on the CAN network: three control signals (Start, Stop and Enable) and four feedback signals (Fault, At Speed, At Freq. and At Pos.). An isolated power and ground bus on the TGPU is powered by a 12V supply from the axial drive. The axial CAN and control signals to the axial drive are optically isolated from rest of the TGPU and use the +5V isolated power for the output stages of the optoisolators. A detection circuit with read back via TGP processor is provided to determine if the isolated 12V power is being supplied to the TGPU. An 82527 CAN controller interface IC is used to provide CAN communications to the axial drive. The interrupt signal, “AX_DR_COMM_INT*”, for the 82527 is sent to the TGPU. To activate the control signals to the axial drive, the appropriate terminals on the axial drive need to be shorted together. Since the signals are polarized, optocouplers with transistor output stages are used to short the terminals together.

Note that the axial drive enable signal is forced inactive by any one of these signals: an overspeed condition, the watchdog circuit being inactive, a disabled axial drive enable switch, an open loop contactor or an axial drive fault. The feedback signals provided by the axial drive are contact closures which must be detected. The input of a Schmidt Trigger is tied by resistor to either power or ground such that the output is inactive. When the contact is closed the input to the Schmidt Trigger is pulled such that the output is active.

The CPU receives signals from thermal sensors: one (LM35DM) is located on the board itself, and the other (LM35DP) is located outside the board.

• Temperature measurement range: 5 – 65.0 degrees C

• Accuracy: +/- 1.0 degree C The signals are converted to digital data by the CPU built-in A/D converter

The TGPU will be able to measure the Gantry Balance using 2 separate piezoelectric devices that indicate a difference in voltage due to the vibrations it senses. These voltages will be amplified on the TGPU and then send to the A/D component.

A +24Vdc input signal from the PDU that indicates the customer room door interlock is open. This signal dynamically tracks the status of the interlock circuit on the TGPU.

A phase under voltage / open fuse detection circuit on the PDU Control board shall monitor the status of the three fuses described above. If the voltage w.r.t. ground on any one or more phases drops below 185Vac (~70% of nominal) the PDU Control board shall detect and latch a PH_LOSS_UV condition and shall issue a "PHASE_LOSS" fault signal to the system.. If contactors Kxg and/or Kss (described above) are closed, the control board shall open them.

A Buss Fault detection circuit on the PDU Control board shall monitor the status of the HVDC. If the differential buss voltage does not exceed 200Vdc within the first 200mS after turn-on the PDU Control board shall detect and latch a BS_FLT condition and shall issue a "BUSS_FLT" fault signal to the system. If contactors Kxg and/or Kss (described above) are closed, the control board shall open them.

Latched +24Vdc output signal to Gantry that indicates the input transformer has overheated. The Control Board will automatically trip CB1 and shut down the system after the assertion of this signal. Cycling power resets this latched fault signal.

Steady-state +24Vdc input signal from the Gantry to indicate the HVDC Bus is enabled. Used by service to bypass firmware control and allow manual control of the HVDC Bus within the NGPDU.

Tilt position feedback is provided by a 5-turn potentiometer.

Sensors are mounted on the front and rear of the gantry. When the sensors are not pressed the impedance is 20k Ohms. When the sensor is pressed, the resistance becomes near 0 Ohms. This signal will be decoded on the board, first to indicate that the maximum impedance of the sensor is 40k Ohms (fault condition). Second that the sensor is not a short circuit (interference condition). This is done for both the front and rear sensors. This information is passed through a register on the TGPU board. If there is interference or a fault condition both elevation and tilt will be disabled.

The TGPU board will intercept the signals that currently go to the tilt elevation amp form the TGPU board. The signals required for generating tilt (forward and backward) will be decoded and sent to the tilt relay board. Also the signal enabling elevation will also be intercepted and another enable will be created so that the TGPU board can disable elevation if the interference sensor is in fault or interference is detected.

The operator will be able to prescribe a tilt command from the SCIM Board. The Prescribed Tilt board (2269601) detects the status of the push button, either pressed or released, in the SCIM keyboard by the use of two independent paths. Only one hardwire line and now the serial communication will be used. There are still two paths for redundancy, but one by firmware and other by hardware.These two paths would be detected and used to tilt or not tilt. Once the signals are received the redundant path will be sent or transmitted to the TGPU board so that a single point of failure cannot cause tilt motion. The defined voltage level of the prescribed tilt signal shall not be greater than 5vdc. The prescribed tilt signal will maintain active as long as the button is pressed.

The TGPU will receive one hardwire signal lines and a serial to initiate remote tilt. When both signal lines are active, a signal is sent to the processor. The processor must check for a stuck button condition. There will also be a line that will indicate fault status of the prescribed tilt input to the board

Tape switches have been added to the tilting base of the gantry to detect if cables on the rotating base are contacting the tilting base. The tape switches will provide an interrupt to the TGPU when the switches are actuated.