Abstract: To maintain tension on a fiber tow as it travels between a spool of the tow and a fiber placement head in a computer controlled fiber placement machine, closed tension loop servo control tow velocity feed forward is provided to control spool rotation so as to not only provide closed loop tension control but to also cause rotation in anticipation of expected tow movement such as due to tow payout upon commanded movements of the fiber placement head. Gain scheduling based on spool radius is also provided. Additionally, a compliant roller is provided to reduce tension dips and spikes from disturbances on the tow, and an inner velocity loop is included with the closed tension loop to provide more effective control of tow tension. The servo control is reconfigurable into an open or pseudo-closed loop mode with a safety low power supply to slowly reel-up slack tow after tow threading, for example, and to otherwise maintain low tension on the tow to hold it in the machine while allowing servicing thereof.

Abstract: A method and apparatus are provided for measurement of absolute position of a moveable machine member wherein output signals of a plurality of position measuring devices are selectively connected to an interface circuit. Each position measuring device produces output signals representing relative position of a device armature and device stator. The position measuring devices are coupled to the machine member so that the absolute position of the machine member anywhere within its range of motion may be uniquely determined from the output signals. A control signal is produce to control the selection of the output signals to be connected to the interface circuit which, at any instant, receives the output signals of a single position measuring device.

Abstract: A method and apparatus are provided for managing a plurality of analogue signals for digital control. Analogue input signals received from a process are periodically sampled and converted to digital input signals for access by a digital control. Digital output signals produced by the digital control are converted to analogue output signals and stored for continuous availability to a controlled process. The sampling and conversion of analogue input signals as well as the conversion and storage of analogue output signals is conducted asynchronously relative to the activity of the digital control by a predetermined program of control signals repetitively produced in response to a clock signal.

Abstract: A method and apparatus for absolute position measurement for numerically controlled machines is provided. The invention produces a unique measurement signal for all locations within the range of a movable machine member using two measuring devices. Each measuring device produces a unique measurement signal within a portion of the range of motion that cyclically repeats over the entire range of motion. The measuring devices are so arranged that the measurement signal of one completes no more than one more cycle over the range of motion than the measurement signal of the other. The difference between the two measurement signals is unique for all locations and is used to produce an absolute position signal.