Transducer access control system

A transducer access control system for use in a disk recording/reproducing apparatus for moving a transducer a required distance from its present position over a disk in the radial direction thereof, includes a linear motor for driving the transducer, a circuit for generating a distance signal indicative of the required distance for moving the transducer, and a calculator for calculating a half distance which is a half of the required distance. To move the transducer for the required distance D, the linear motor is operated at the velocity controlled in accordance with a reference velocity signal produced from a reference velocity generator. The reference velocity is determined such that, the reference velocity is maintained at a predetermined value during the movement of the transducer in the first half of the required distance, and gradually decreases during the movement of the transducer in the second half of the required distance.

BACKGROUND OF THE PRESENT INVENTION 
1. Field of the Present Invention 
The present invention relates to a transducer access control system for use 
in a disk recording/reproducing apparatus for moving a transducer a 
required distance from its present position over a disk in the radial 
direction thereof, and more particularly, to a transducer access control 
system providing highly reliable rapid rough access using reference 
velocity data which varies relatively to the distance moved by transducer. 
2. Description of the Prior Art 
In general, rough access and precision access control systems are applied 
in devices for recording and playing back data from a disk-type recording 
medium provided with data tracks formed either concentrically or spirally 
in a radial direction. Each track is divided into multiple sectors which 
are the smallest access unit. Rough access is executed to move the 
transducer into the vicinity of the target position and is followed by a 
precision access, locating the transducer at the final target position. 
Rough access drive may be accomplished by a linear motor or other device. 
Furthermore, if the rough access is accomplished with high precision and 
reliability, the access time for the precision access can be reduced, 
resulting in the reduction of the total access time. 
Furthermore, acceleration and deceleration with conventional rough access 
control is accomplished by time referencing. However, there is a limit to 
the precision which can be obtained with acceleration/deceleration control 
using time referenced control. 
Furthermore, when the velocity of the transducer is detected, the periods 
between the output pulses from the scale are counted and the velocity is 
calculated from this count. There is, therefore, a delay in the control 
response equivalent to the time required for the calculations to be 
performed. 
Thus, a transducer access control system designed to resolve these and 
related problems is proposed, for example, in Japanese Patent Application 
No. 62-113383 assigned to the same assignee as the present application. 
Proposed in this application No. 62-113383 is a system provided with a 
transducer which records data to and reads data from a recording medium, a 
travel signal generating device which generates a travel signal 
corresponding to the travel of the transducer and a velocity detection 
means which detects the travel velocity of the transducer. A counting 
device counts the output from the travel signal generating device and a 
median position detection device detects the median value of the access 
distance based on the count obtained by the aforementioned counting 
device. A reference velocity generating device generates a triangular 
velocity pattern (FIG. 6) which gradually increases the reference velocity 
during the first half of the rough access operation and gradually 
decelerates the reference velocity during the later half of the rough 
access operation. A comparison device compares the reference velocity 
generated by the reference velocity generating device with the travel 
velocity detected by the velocity detection device, and a drive device 
adjusts the travel velocity of the transducer based on the comparison 
result of the comparison device. This system uses the relationship between 
the physical position data of the transducer and the velocity data of the 
transduce as to accomplish the rough access with good precision by 
providing reference velocity data. 
However, in the aforementioned access control system, as shown in FIG. 6, 
the reference velocity is outputted from the reference velocity generating 
device in such a manner that the velocity increases in the first half to 
median point 603, at which point a maximum velocity is reached, and then 
decreases in the later half from median point 603 in a so-called 
"triangular control" system, and thus, efficient, high speed access at the 
maximum capacity of the drive means is not possible. 
SUMMARY OF THE INVENTION 
Thus, the object of the present invention is to provide a transducer access 
control system which, in addition to providing high precision rough 
access, is capable of accelerating at the maximum capacity of the drive 
device and is thus capable of high speed access, and which can suppress 
over-acceleration. 
In order to achieve the aforementioned objectives, according to the present 
invention, a transducer access control system for use in a disk 
recording/reproducing apparatus for moving a transducer a required 
distance from its present position over a disk in a radial direction 
thereof, comprises a driving device for driving the transducer; a velocity 
detection means for detecting an actual velocity of the transducer and for 
generating an actual velocity signal; a position signal producing device 
for producing a position signal indicative of a position of the 
transducer; a required distance generating device for generating a 
distance signal indicative of the required distance for moving the 
transducer; a calculation device for calculating a half distance which is 
a value equal to half of the required distance and for producing data 
corresponding to the half distance; a reference velocity generating device 
for generating a reference velocity signal indicative of a reference 
velocity which is determined relatively to the data from the calculation 
device such that the reference velocity is maintained at a predetermined 
value during the movement of the transducer in the first half of the 
required distance and gradually decreases during the movement of the 
transducer in the second half of the required distance; and a comparator 
for comparing the reference velocity signal with the actual velocity 
signal and for producing a difference signal which is applied to the 
driving device.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a block diagram of a access control system according 
to the present invention is shown. In the drawing, reference number 101 is 
a disk-shaped recording medium which has concentric or spiral data 
recording tracks formed radially on the disk, each track being divided 
into multiple sectors, the sector being the smallest access unit. Item 102 
a transducer which has a head, pickup, or similar device used to record 
data to or read data from the recording medium 101. Item 103 is a head 
moving arrangement which moves the transducer 102 along the recording 
medium in a radial direction and is preferably carried out by a linear 
motor 103' shown in FIG. 2. Item 100 is a access request circuit for 
producing a required access distance data D representing a transducer 
access distance for the transducer as requested by the operator or set in 
a program. Item 104 is a rough access controller for controlling 
transducer 102 to move roughly to the requested position P1 from the 
present position P0 in accordance with the access distance data D 
(=P0-P1), shown in more detail in FIG. 2. Item 107 is a host device such 
as a host precision access; 106 is a drive controller which controls the 
device overall; and 107 is a host device such as a host computer which 
controls the drive device. 
Referring to FIG. 2, a detail illustration of the rough access controller 
104 is shown which is connected to a linear motor 103' provided in the 
head moving arrangement 103 for moving the transducer 102. In FIG. 2, 
reference number 202 is a velocity detector which detects the velocity 
(including information on degree and direction) of linear motor 103'; and 
203 is a scale which detects the travel distance and direction of linear 
motor 201, and which generates pulses according to the travel and 
direction of linear motor 103' moving the transducer 102. Preferably, 
scale 203 is defined by a plate scale having a predetermined pitch 
markings and provided to move in accordance with the linear motor 103', 
and a pair of fixed sensors so that the plate scale moves adjacent the 
sensors. The sensors detect the markings to produces pulses. Thus, by the 
number of pulses produced from each sensor the amount of movement of the 
linear motor 103' is detected and the order of the pulses produced from 
two sensors indicates the direction of movement of the linear motor 103'. 
Furthermore, reference number 204 is an up-down counter for counting the 
number of pulses generated by the scale 203 so that the contents of 
counter 204 represents the present position P0 of the transducer 102. Item 
205 is a reference velocity table defined, e.g., by a memory such as a ROM 
which contains a reference velocity pattern and generates a reference 
velocity Vr which is based on the value counted by counter 204, 
particularly on the actual travel distance of linear motor 201 and also on 
the access distance D. Reference number 206 is a digital-to-analog 
converter for converting the digital output signal of reference velocity 
table 205 to analog form. Reference number 207 is a comparator which 
compares the output value of velocity detector 202 representing the actual 
velocity Va of the linear motor 103' with the reference velocity Vr as 
generated by reference velocity table 205. Item 208 is a driving circuit 
for driving linear motor 103' based on the output signal from comparator 
207, and item 210 is a median point detector which detects half the 
distance (1/2D) of the access distance D based on the access distance data 
D obtained from the access request circuit 100 and also detects the median 
point, a point between P0 and P1, based on the output of the counter 204. 
Reference number 209 is a controller which controls these respective 
devices. 
In operation, when a transducer access command is received from host device 
107, drive controller 106 executes rough access positioning when the need 
for rough access is recognized. At this time, access request 100 generates 
access distance data D which is applied to median point detector 210. 
Accordingly, median point detector 210 calculates a distance 1/2D which is 
equal to one-half the access distance D based on the access distance data 
D, and also calculates an exact median point, a point between P0 and P1, 
to be expressed by the value of counter 204. More specifically, median 
point detector 210 calculates a distance 1/2D, and first and second 
reference amounts that will be realized in counter 204 when the linear 
motor 103', i.e., transducer 102, has moved the distances 1/2D and D, 
respectively, from the present position. Furthermore, at this time, 
controller 209 initializes the other devices (step 301 in FIG. 3). 
As shown in FIG. 4, according to the present invention, the velocity 
pattern for the required reference velocity Vr is such that it starts from 
the maximum velocity (point 401) which is equal to the median summit 
velocity (point 603) in conventional triangular velocity pattern (FIG. 6) 
and keeps the maximum velocity until the transducer is moved to a median 
point between the initial position P0 and the target position P1 and, 
thereafter, the reference velocity Vr decreases. Thus, the actual velocity 
Va of the linear motor 103' at the beginning rapidly increases the 
velocity to reach the maximum velocity (level 401), as indicated by a 
dotted line in FIG. 4. Accordingly, when compared with the conventional 
system, the access time can be reduced. 
Thus, according to the present invention, because the reference velocity 
table 205 produces reference velocity Vr which is extremely high during 
the initial acceleration period, the output of comparator 207 is so high 
(saturated) that driver 208 operates at its maximum capacity, thereby 
enabling the high acceleration of the linear motor. Moreover, because the 
maximum velocity which should be attained at median point 403 is not 
exceeded, loss of deceleration control caused by over-acceleration will 
not occur. 
In order to control the linear motor 103', and in turn the transducer 102, 
in the above described manner, the reference velocity table 205 must be 
provided with enormous amount of patterns for different access distances, 
resulting in excessively large size table. 
Therefore, according to the preferred embodiment of the present invention, 
median point detector 210 is provided in association with counter 204 to 
detect the median point so as to minimize the size of the reference 
velocity table 205, as explained below. 
The reference velocity table 205 of the present invention carries a Vr-D 
relationship table, an example of which can be expressed by a line K shown 
in FIG. 5 in which the axis of the abscissas shows the travel distance 
during rough access, and the axis of the ordinates shows the reference 
velocity data. When a transducer access distance D1 is provided from 
access request 100, median point detector 210 calculates a half distance 
1/2D1, and, at the same time, first and second reference amounts that will 
be realized in counter 204 when the linear motor 103' (transducer 102) has 
moved the distances 1/2D1 and D1, respectively, from the present position 
are also calculated. Based on the calculated data 1/2D1, reference 
velocity table 205 finds on line K a corresponding velocity Vr(1/2D1) 
which is produced from table 205 until linear motor 103' moves the 
distance 1/2D1, that is until counter 204 has realized a value equal to 
the first reference amount. When linear motor 103' has moved to the median 
point of the required access distance D1, the reference velocity Vr as 
produced from reference velocity table 205 gradually decreases by reading 
the data on line K in the direction of arrow 501 relatively to the 
travelled distance. Then, when the contents of the counter 204 becomes 
equal to the second reference amount, drive control 106 produces a signal 
to drive 208 to stop the linear motor 103'. 
Similarly, when a transducer access distance D2 is provided from access 
request 100, the same table represented by line K is used. At first, 
median point detector 210 calculates a half distance 1/2D2, and, at the 
same time, first and second reference amounts that will be realized in 
counter 204 when the linear motor 103' has moved the distances 1/2D2 and 
D2, respectively, from the present position are also calculated. Based on 
the calculated data 1/2D2, reference velocity table 205 finds on line K, a 
corresponding velocity Vr(1/2D2), which is produced from table 205 until 
linear motor 103' moves the distance 1/2D2, that is until counter 204 has 
counted to the first referenced amount. When linear motor 103' has moved 
to the median point of the required access distance D2, the reference 
velocity Vr as produced from reference velocity table 205 gradually 
decreases by reading the data on line K in the direction of arrow 502 
relatively to the travelled distance. Thereafter, the linear motor 103' 
stops when counter 204 counts to the second reference amount. 
Thus, it is not necessary to use a new velocity data table for each travel 
distance. If the maximum access distance is Dmax in this device and the 
reference velocity table includes up to reference velocity Vr(1/2Dmax), 
the table can be applied to all rough access distances, and a small 
capacity ROM is sufficient to store the reference velocity table 205. 
In the circuit of FIG. 2, when rough access begins (step 302), counter 204 
begins counting the pulses from scale 203. The output of counter 204 is 
applied to reference velocity table 205 in which the counted result is 
compared with the first reference amount so as to detect when the linear 
motor 103' has moved to the median point. Until then, a reference velocity 
Vr corresponding to level 401 (see FIG. 4) is continuously read regardless 
of the count. Thereafter, when the linear motor 103' has moved pass the 
median point, a reference velocity Vr as produced from reference velocity 
table 205 decreases gradually along line K relatively to the travel 
distance of the linear motor. 
The digital reference velocity data Vr as produced from reference velocity 
table 205 is converted to analog form by D/A converter 206 so that it can 
be compared with the output of velocity detector 202 by comparator 207. 
Comparator 207 compares the output of D/A converter 206 with the output of 
velocity detector 202, and produces a difference signal for driver 208. 
Driver 208 drives linear motor 103' according to this difference signal. 
The actual velocity data Va of linear motor 103' is detected by velocity 
detector 202, and is fed back to comparator 207, thereby defining a 
control closed loop to make the actual velocity Va of linear motor 201 
follow the reference velocity Vr. 
When counter 204 has counted to the second reference amount, rough access 
processing is completed (step 303). 
A transducer access control system according to the present invention is 
capable of high precision and reliable rough access by utilizing the 
relationship between velocity data and data identifying the physical 
position of the transducer. 
Furthermore, according to the present invention, because a closed loop is 
formed using the velocity detector and comparator, a real time control 
requiring no delay is possible. 
Furthermore, according to the present invention, since the reference 
velocity pattern is such that for the first half distance a maximum 
velocity is requested, and for the second half distance a gradually 
decreasing velocity is requested, the transducer accelerates at the 
maximum capacity of the driving means, i.e., the linear motor, to the 
median point. Moreover, the transducer is controlled so as to not exceed 
the velocity which should be attained at the median point. The time to the 
median point is therefore shorter than that in conventional triangular 
control methods, thus high speed access is possible, and system efficiency 
can therefore be increased. Furthermore, because the velocity which should 
be achieved at the median point does not exceed the maximum possible 
speed, loss of deceleration control due to over-acceleration does not 
occur. 
Although the present invention has been fully described in connection with 
the preferred embodiment thereof with reference to the accompanying 
drawings, it is to be noted that various changes and modifications are 
apparent to those skilled in the art. Such changes and modifications are 
to be understood as included within the scope of the present invention as 
defined by the appended claims unless they depart therefrom.