Abstract:
A single loop servo is used for positioning a lens holding element with respect to an optical disk. The dynamic range of the error signal used in the positioning is dynamically frequency shifted such that the servo summing of the error signal with a reference signal (velocity reference) is always performed within the same dynamic range. This action simplifies circuit operation as the dynamic range of the error signal is compressed at high speeds. Two embodiments of the invention are described.

Description:
This application is a continuation in part of Ser. No. 07/528,527, filed May 25, 1990, now abandoned. 
    
    
     DOCUMENT INCORPORATED BY REFERENCE 
     U.S. Pat. No. 4,839,876 by Fennema is incorporated for its showing of a single loop servo positioning system in an optical disk environment in which the present invention is most advantageously employed. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to servo positioning systems, particularly to those servo positioning systems adaptable or particularly useful in recording devices. The present invention relates to a servo positioning control and system which utilizes but a single servo loop for a stop lock position (track following) and for a traversing (track seeking) control. 
     DISCUSSION OF THE PRIOR ART 
     Positioning servos have been used for many applications, some of which include magnetic and optical recorders. Most servo positioners have a so-called stop-lock position wherein the tool, transducer or lens, is held at a relatively stable position and a moving mode, which for recorders is termed track seeking. Many of the servo positioners employ a first control loop for the stop lock position and a second control loop in a seeking or moving mode. Switching between the two loops can induce undesired transients, as well as require a substantial number of circuits for the two respective loops. It is desired to use a single loop for both the stop lock and moving functions of servo positioners. 
     The document incorporated by reference Fennema shows a single loop control for an optical disk recorder which is position controlled throughout; that is relative position of the lens to a track or set of tracks is an independent input variable. It is desired to provide a single loop servo positioning control which uses a velocity mode in the track seeking or traversing function, yet provides an effective stop-lock control. 
     Another single loop servo positioning control is shown by Matla, et al. in U.S. Pat. No. 4,217,612, which always uses a position error input for controlling the servo; that is, the relative position of a transducer to the magnetic disk, is the independent input variable to be compared with a reference for effecting servo actions. Matla, et al. is cumulative with respect to Fennema. Koenig, U.S. Pat. No. 4,607,201, shows a track- following position control loop i.e., always providing for stop-lock; since the reference does not provide for seeking, it is not pertinent to any of the claims of the present application. Stephens, et al., U.S. Pat. No. 4,575,776, shows a seek or movement control for a positional servo in which a simulated position error signal is used. Hsieh, et al., U.S. Pat. No. 4,435,797, shows a servo position scheme of a classical type in which a separate servo loop is provided for track-following (stop lock) and for seeking. It is known that such separate seek loops have used velocity profile controls for controlling the seek while the track following (stop lock) controls use position error controls. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a single-loop positioning control in which all modes are controlled by a velocity profile. Stop-lock is controlled by a velocity signal of zero while the velocity control of the loop is provided in a manner for minimizing the dynamic range required in the circuits. 
     In a positioning servo system for relatively positioning first and second relatively movable members using a motive means operatively connected to the movable members has means for providing an error indicating signal to control the servo which includes a single-loop servo system and sensing means for sensing the relative position of the relatively movable members for indicating the relative position by a position error signal. Servo means process the position error signal in a single-loop having dynamic range changing means for changing the dynamic range of the position error signal and includes position control means connected to the processing means for receiving the dynamic range changed position error signal and for generating a servo drive signal. Output means connected to the position control means receives the servo drive signal for restoring the dynamic range of the servo drive signal to the dynamic range of the generated position error signal. The output means is also connected to the motive means to supply a restored dynamic range servo drive signal to the motive means. 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a simplified block diagram of a servo positioner using the present invention in an optical disk recorder. 
     FIG. 2 is a block diagram of a non-linear range-change servo used in the FIG. 1 illustrated system. 
     FIG. 3 shows a filter-frequency shifted (linear and range-change servo amplitude expansion (non-linear) circuit. 
     FIG. 4 shows a range selection circuit usable in the FIG. 1 illustrated embodiment. 
     FIG. 5 is a circuit diagram showing a switchable attenuation network used in the FIG. 4 illustration illustrated circuits. 
    
    
     DETAILED DESCRIPTION 
     Referring now more particularly to the drawing, like numerals indicate like parts and structural features in the various Figs. An optical disk 10 is mounted for rotation on frame 11 as indicated by dashed line 12. A motor (not shown) suitably rotates the disk 10 speed. A head arm 13 is movably mounted on frame 11 and carries a lens supporting actuator 14 as indicated by dashed line 15. Laser means (not shown) provide a laser beam through the actuator 14 supported lens to travel over bi directional light path 16 to optical disk 10. Optical disk 10 reflects the laser beam along path 16 returning it through the lens (not shown) of actuator 14, thence over light path 18 to a so called quad detector 17. Quad detector 17 consists of four electrically-independent elements A-D. The four light-responsive elements supply separate signal(s) which are combined, using known techniques, to indicate track crossings in a so-called tracking error signal (TES) supplied over line 21. Elements A-D are independently connected to a usual decode circuit, represented by the vertical line at the end of line 21, to generate TES. The TES on line 21 goes through linear amplifier 22 to be supplied over line 30 to range change servo action circuit 23. Circuit 23 responds to the measured or indicated radial speed of laser light beam on path 16 with respect to disk 10 for changing the dynamic rang of TES to a center or reference range, as will become apparent. In this manner all actions in the servo loop for controlling actuator 14 occur within the same dynamic range. Upon completion of the servo control action, the dynamic range of a generated device signal is again changed to the original range of TES and supplied through the usual servo compensator 24, thence through amplifier 25 and over line 26 for being supplied to actuator 14. The document incorporated by reference shows a suitable lens support and actuator 14, as well as its relationship to head arm 13. 
     FIG. 2 shows TES on line 30 being supplied first to a differentiating filter 31 of the zero-pole type. A dynamic-range control signal on line 45A of line group 45 controls the filter 31 to adjust its operation such that its output signals are dynamic range shifted in accordance with the radial speed of the beam 16 as it traverses radially over disk 10. Range circuit 32 also decreases the dynamic range with radial speed; i.e. both filter 31 and range circuit 32 compress the TES dynamic range. The filter 31 action adjusts dynamic range in steps by stepped attenuator 60 control, as will become apparent. As seen in FIG. 4, filter 31 and range circuit 32 are integrated into one circuit. During track seeking, this range-changed TES travels over line 33, to sample and hold circuit 36. During track seeking, the timed operation of sample and hold circuit 35 can be by an independent oscillator 37 timed to the zero axis crossings of TES on line 30. During track following, a signal on line 38 continuously enables sample and hold circuit 36. The line 38 signal is the usual track following signal commanding a track follow operation. 
     Sample and hold (S+H) circuit 36 supplies its output to circuit 39. Circuit 39 has a dynamic range decompressing portion 56 which processes the S&amp;H circuit 36 signal to expand the dynamic range to its original range. Note that circuits 32 and 56 operate identically with the filters 31 and 41 zero pole and pole zero providing dynamic range scaling of the signal being processed. Summing circuit 40, in circuit 39, compares the velocity profile circuit 46 signal with the velocity over signal to produce the usual servo correction signal to be dynamic range scaled by integrating filter 41 pole zero to supply a usual servo control signal over line 42. The range scaling is by shifting the zero-poles in filters 31 and 41. 
     FIG. 3 shows a second and preferred embodiment of the invention. TES is received over line 30 into the differentiating zero-pole filter 31 which is controlled by a range select signal on line 45A received from range select circuit 60, later described. Dynamic range compressing circuit 32 non linearly compresses the dynamic range of TES to create a range-changed TES. This range-changed TES is supplied to rectifier 51 for use during the seek mode. The range-changed TES travels directly to terminal 55 of switch 54 for use during the track-follow mode. Switch control circuit 61 actuates switch 54 to move to one of the three terminals, as will be later described. In the track seeking mode, a rectified signal having a first polarity on line 52 is used in a radially inward seek, switch 54 then connects line 52 to range circuit 56. For a radial outward seek, the opposite polarity rectified signal from rectifier 51 supplied over line 53 to switch 54 center terminal is connected to range circuit 56. During track-following (stop-lock), switch 54 connects line 55 directly to range circuit 56. This connection supplies the range-changed TES without alteration for track-following control. Thus, there are three servo modes within the single servo loop. A track-following mode (switch 54 connects line 55 to range circuit 56) at which the velocity profile or reference circuits 46 apply a zero reference velocity to summing circuit 40; first seek mode in the radial inward direction, switch 54 connects line 52 to range circuit 56 and a second seek mode in the radial outward direction in which line 53 is connected by switch 54 to range circuit 56. Switch control 61 receives a direction or command control over line 63 to indicate direction of seek while the seek or no seek signal on line 62 controls velocity profile circuits 46 to supply signals in accordance with a predetermined velocity profile to sum circuit 40 or to provide a zero velocity reference signal during track following. A mode control signal in line 62 activates circuit 61 to set switch 54 as described above. Generating seek direction signals and track following signal modes is in accordance with the usual procedure. 
     FIG. 4 illustrates the operation of the range shifting filters 31 and 41. These filters operate substantially the same, therefore, only filter 31 is described. It is understood that the change between the integrating filter and the differentiating filters is well known and can be readily implemented. TES on line 30 goes through resistor 70 to operational amplifier 71. Line 45 of FIGS. 2 and 3 consist of two lines 72 and 75 for each filter 31 and 41. Line 72 signal carries a signal from the output of operational amplifier 7 to the input of switchable attenuator 60 (FIG. 5). The signal on line 75 from switchable attenuator 60 goes through capacitor 74 to the amplifier 71 input at resistor 70 and is fed forward through capacitor 76 to the amplifier 79 input at resistor 77. Resistor 77 is also connected to the output of operational amplifier 71. A reference input to operational amplifier 71 includes the reference voltage V1 connected to a second input of the operational amplifier. Switchable attenuator 60 responds to the sensed velocity signal on line 89 to select range controls for filters 31 and 41 and velocity profile circuit 46. The line 89 signal is supplied by known sense velocity circuit 88. Circuit 88 derives the speed or velocity signal from the line 21 signal in a known manner, i.e. measures either the frequency or wavelength of the tracking error signal on line 21 to produce a speed indicating signal. One example of sensing the relative radial speed of an optical head lens, lens support and actuator 14 and disk 10 is shown in U.S. Pat. No. 4,914,725. Other speed or velocity sensing circuits may be employed, as is well known. A non-range changed velocity profile can be used for activating attenuator 60 to change ranges. 
     Switchable attenuator 60 determines the operation of filter 31 by adjusting the operation of operational amplifiers 71 and 79. The output stage of filter 31 consists of operational amplifier 79. Operational amplifier 71 supplies its output signal via resistor 77 to a first input of amplifier 79. A reference signal V1 is supplied to a second input of operational amplifier 79. A bridge circuit 84-86 connects the output line 33 of amplifier 79 to its first input at resistor 77. Oppositely poled diodes 85 and 86 connect the output line 33 to resistor 84 through to resistor 78. Diodes 85 and 86 constitute a non linear dynamic range change in their control of output amplifier 79. Diodes 85 and 86 operate identically in each shifted range of filters 31, 41. Attenuator 60 coacts with the circuit elements 71-77 to dynamically change the effective or apparent capacitance of the FIG. 4 illustrated filter. This capacitance change shifts the frequency of the filter to change its dynamic range scaling. 
     FIG. 5 shows switchable attenuator 60. Switchable attenuator 60 includes three separate attenuator circuits 91, 92 and 93 respectively for filters 31 and 41 and velocity profile circuit 46. Lines 45A, 45B, and 45C respectively connect the attenuator circuits 91-93 to their respective controlled circuits as best seen in FIGS. 2 and 3. All circuits 91-93 operate in synchronism to select the same attenuation, as will become apparent. Each of the circuits 91-93 are identical, except that the attenuation factors are related to the operation of the respectively controlled filters 31, 41 and velocity profile circuit 46. Circuit 91 is explained, it being understood that the explanation applies to all circuits 91-93. The seek velocity indicating signal on line 89 (from circuit 88 as above described) is supplied to electronic switch 100. Switch 100 is designed to respond to the line 89 signal to selectively connect line 75 (hence line 45A) to input line 72 without attenuation via terminal 101 (slow seek velocity), via 1/10 attenuator 110 by terminal 102 during a relatively high speed portion of a seek or traversal, by 1/100 attenuator 111 by terminal 103 during yet higher speed seeks. Terminal 104 and ellipsis 112 indicate that yet greater attenuations may be employed for enabling a greater velocity of traversal while maintaining servo circuit operation in one dynamic range. Lines 115 and 116, respectively for circuits 92 and 93, correspond to input line 72 or circuit 91. Note that by range changing the output signal of profile circuit 46 to sum circuit 40, all servo parameters are dynamic range changed to be consonant with each other. The components of switchable attenuator 60 may be incorporated into filters 31, 41 and velocity profile circuit 46. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention: