A control loop provided with a control unit for realizing a transfer characteristic having a number of peaks at a fundamental frequency and harmonics thereof. The control unit comprises a memory device for digitally storing a number of samples of the error signal appearing in the control loop during a cycle period equal to the period corresponding to the fundamental frequency. Furthermore, there are provided means for comparing the sample stored in the memory device with the value of the error signal one cycle period later and, depending on this comparison, correcting the memory content of the relevant memory location. The variation of the error signal stored in the memory device is furthermore cyclically employed as a control signal for the control device included in the control loop.
A tracking error signal generating apparatus for use in a recording and reproducing system employing a disk on which is formed an information track comprising a pair of tracking markers and a time-division servo signal including a sync signal. An error is calculated from any two of the tracking marker data obtained from the disc and a series of error data is generated. Furthermore, a series of corrected error data is generated by respectively inserting at least one neighboring value of adjacent two data between the adjacent two data of the error data, and each of the corrected error data are converted to form an analog signal.
A control process to keep input and output of the whole control system equal while measuring the input-output characteristics of the object to be controlled during the blanking time of the equipment in operation as the measuring mode period, by writing and memorizing the measured input as the data of a random access memory and the measured output as the address of the RAM, and by using the RAM as the inverse function table memory during the control mode period that follows the measuring mode period.
A device according to the invention for scanning a rotating information carrier (2) comprises a transducer (10) and controller (20, 22) for controlling a scanning parameter of the transducer (10), such as the radial position and the setting of a focus. The controller comprise difference signal generator (20) for generating a difference signal (RE) which is indicative of a difference between a current value and a desired value of the scanning parameter, and correction signal generator (22) for generating a correction signal (S.sub.C) in response to the difference signal. The correction signal generator (22) comprise a delay loop (25) having first in first out memory (36) for generating a delayed signal (S.sub.DL1) and feedback filter (38) for filtering the delayed signal (S.sub.DL1). The device comprises rotation speed detector (8) for generating a clock signal (CL) having a frequency which is indicative of the rotation speed of the information carrier (2), the delay in the memory (36) being proportional to a period of the clock signal.
A focusing control apparatus has a controller and a memory so as to store the control signal of a previous step in the memory. The control signal detected by a photo-detector is changed according to the changes of temperature and light intensity input from a light source. The apparatus performs focusing control by summing in an adder signal output by the controller, which signal is the stored signal on which a computation has been performed, and the new signal input. The apparatus detects and controls an offset signal of the focusing error signal by providing a low-pass filter between the adder and the controller. A feedback circuit including an anti-aliasing circuit is further provided between the output of the adder and the controller, whereby a new focusing control signal is transmitted by correcting the signal stored in the memory after a computation has been performed thereon by the controller. Therefore, the focusing control signal transmitted to the driver of the object lens is stably maintained and the design of a control compensator can be simplified by the use of the feedback circuit.
A head positioning system capable of positioning a magnetic head at the center line of a target track of a floppy disk at high speed, in which a positioning controller prepositions the magnetic head within a predetermined distance from the center line of the target track based on a position error signal indicating the deviation of the magnetic head from the center line of the target track. A positioning compensation controller generates a compensation signal whose frequency is twice the disk rotational frequency so that the positioning compensation controller positions the magnetic head at the center line of the target track. A switching compensation controller connected to the positioning compensation controller enables the compensation signal to equal the output of the initial positioning controller during the prepositioning operation.
