Sectional X-ray table having dual servo drives

An X-ray table system for moving a patient through an X-ray beam path at constant velocity comprising:

• a base, an elongated support mounted on the base for moving longitudinally, and an elongated patient cradle means mounted on the support for moving longitudinally relative to the support and to the base,
• a reversible support drive motor (support motor) and means coupling said motor in driving relation with the support,
• a first tachometer (support tach) for producing an analog signal representative of the rotational speed of said support drive motor and the velocity of the support,
• a reversible cradle drive motor (cradle motor) and means coupling said motor in driving relation with said cradle means for said motor to move said cradle means longitudinally relative to the support,
• a second tachometer (cradle tach) for producing an analog signal representative of the rotational speed of the cradle motor and the velocity of the cradle means relative to the base,
• servo amplifier means (support servo) for supplying electric power to said support motor, said support servo having a plurality of inputs one of which is an input for the analog signal produced by the support tach, and another input,
• another servo amplifier means (cradle servo) for supplying electric power to said cradle motor, said cradle servo having a plurality of inputs one of which is an input for the analog signal produced by the support, another for the analog signal produced by the support tach, and other inputs,
• ramp signal generator means for supplying a selected one of an increasing or decreasing analog ramp signal at predetermined times to said other input of the support servo,
• a digital-to-analog converter (cradle speed DAC) for supplying an analog signal corresponding to desired cradle speed to one of said other inputs to said cradle servo,
• a plurality of switches operable, respectively, in response to said cradle means and said support attaining predetermined positions,
• digital processor means and bus means for communicating digital data and addresses to and from said processor means,
• a source for supplying a selected one of an increasing or decreasing digital ramp signal, under control of said processor means, to said cradle speed DAC to thereby supply said DAC with a ramp signal having digital accuracy for accurately controlling the speed of said cradle motor,
• an encoder operated by movement of said cradle for providing pulse signals representative of the direction of movement and position of said cradle means relative to said base,
• digital position register means for storing digital values corresponding to the position of said cradle means relative to said base and for being read out by said processor means to determine the position of the cradle means,
• decoder means operative to decode the signals from said encoder and to change the digital position values in said position register means in accordance with movements of the cradle means relative to the base,
• a potentiometer for providing an analog signal representative of the initial position of said cradle means when said means is not moving, and an analog-to-digital converter for converting said analog signal to a digital value representative of initial cradle position, and means for entering this position data in said register means for being read by said processor means,
• the operational sequence of said table assembly comprising driving said support first in a forward direction from a retracted positive relative to said base at constant speed to an extended position at the beginning of a transition zone wherein said support motor is decelerated and said cradle motor is accelerated inversely so that the cradle will move forwardly at a constant speed relative to the base even through driving is exchanged between said motors, and for retracting said table assembly the cradle is driven first rearwardly on to the support to the beginning of a transition where cradle motor is decelerated and the support motor is accelerated,
• said processor responding to one of said switches being operated corresponding to said support being retracted by enabling said ramp generator to generate and supply an increasing analog ramp signal to the input of said support servo to cause said support motor to accelerate and said support tach then supplying an increasing analog signal to the other input of said support servo such that when the input signals balance said support motor will be running at constant speed,
• said processor means responding to operation of one of the switches at the beginning of said transition zone by enabling said ramp generator to supply a decreasing analog ramp signal to the input of said support servo to decelerate said support motor with a resulting decreasing analog signal from said support tach,
• said processor means further responding by effecting input of a corresponding digital ramp to said cradle speed DAC for the analog signal therefrom to be supplied to one input of said cradel servo concurrently with the decreasing input signal from the support tach and the increasing signal from the cradle tach such that when said signals balance with the ramp signal said cradle motor drive the cradle means at a constant speed corresponding to the former speed of the support because of the similarity in the slopes of the two ramps,
• said ramp signal generating sequence being provided oppositely for driving said cradle means rearwardly relative to the support and the support rearwardly relative to the base.