GB2110015A - Disk drive system - Google Patents

Abstract

The system includes a motor control circuit wherein an AC synchronous motor (19) is utilized to drive the disk spindle from a source of DC voltage. The motor control circuit is utilized to convert the DC voltage to an AC square wave which is applied to the motor, a crystal- controlled oscillator (22), being utilized to generate the square wave. Since the motor is synchronous to the oscillator output, feedback from the motor is not required. A delay circuit (U5) is provided between the oscillator output and voltage source (20) to eliminate large current surges which would normally appear on the input line of the voltage source. The relatively small sizes of the synchronous motor and the printed circuit board utilized to mount the drive circuit electronics allows both to be mounted far from the disk and read head, the possibility of magnetic fields affecting either being thereby minimized. <IMAGE>

Description

SPECIFICATION Disk drive system This invention relates to a disk drive system and particularly to a constant velocity system wherein only small velocity variations can be tolerated, such as in computer peripherals and, in particular, floppy disk drives.

The floppy disk drives current in use can be conveniently divided into two basic categories, belt drive and direct drive.

Examples of the first category disk drives are those manufactured by Qume Corporation, San Jose, California. In particular, the Qume Trak 842 is a belt-driven, AC powered motor, floppy disk drive and the Qume Trak 542 is a belt driven, DC powered, floppy disk drive using a DC brush motor. In order to obtain correct speed regulation, feedback is necessary for disk-drive operations. The feedback is typically via Hall-effect devices or an AC tackometer-generator. Either of these feedback devices adds to the cost of the disk drive motor control circuits. Additionally, a brush-type motor has problems of short brush life (1,000-5,000 hours) and radiated electromagnetic interference which can cause reduced data reliability and readability.

The direct drive approach, such as the RFD 4001, manufactured by the Remex Division of EX-Cell-O Corporation, Irvine, California, uses a motor mounted directly on the spindle hub or shaft. This reduces motor components and accessories. Since the motor is mounted on the rotating spindle shaft no additional motor bearings are required. A motor pulley, a spindle pulley and the drive belt are eliminated. As with the belt drive device, problems associated with motor feedback are introduced. In the direct drive device, Hall-effect and optical switches are commonly used for feedback (for speed and stability information) with the attendant increase of device cost and complexity and reduced motor reliability. Additionally, since the motor may be mounted on the spindle, the possibility exists of radiated electrical interference from the motor reducing data reliability.Further, the direct drive motor takes up considerable space around the spindle and if it were desired to retrofit a belt drive device to a direct drive device, a major mechanical redesign would be necessitated.

What is desired is to provide a minimum cost disk drive motor which is reliable and which has substantially constant output shaft velocity such that feedback devices are not required in the motor control circuit.

The present invention is applicable to a disk drive system including a motor control circuit wherein an AC synchronous motor is utilized to drive the disk spindle from a source of DC voltage. The motor control circuit is utilized to convert the DC voltage to an AC Square wave which is applied to the motor, a cyrstalcontrolled oscillator being utilized to generate the square wave. Since the motor is synchronous to the oscillator output, feedback from the motor is not required. A delay circuit is provided between the oscillator output and voltage source to eliminate large current surges which normally would appear on the input line of the voltage source.The relatively small sizes of the synchronous motor and the printed circuit board utilized to mount the drive circuit electronics allows both to be mounted far from the disk and read head, the possibility of magnetic fields affecting either being thereby minimized.

It is an object of the present invention to provide a disk drive system which utilizes an AC synchronous motor.

It is a further object of the present invention to provide a rotating memory system utilizing an AC hysteresis synchronous motor powered by a DC voltage source.

It is a still further object of the present invention to provide a disk drive utilizing an AC hysteresis synchronous motor powered by a DC voltage source, the input DC being converted to an AC square wave utilizing a crystal-controlled oscillator.

It is a further object of the present invention to provide a floppy disk drive system which utilizes an AC hysteresis synchronous motor driven by a square wave, a motor control circuit converting a DC voltage supplied by a voltage source to the square wave, the motor control circuit including a delay circuit to prevent current surges in the voltage source input line.

As the state-of-the-art in floppy disk drives continues to advance, suppliers are constantly seeking to reduce costs in order to be costcompetitive. AC synchronous motors, including those of the hysteresis type, are very cost effective and lower in cost over DC brushless motors which are commonly utilized in disk drive systems. In addition, the mechanical dimensions of the motor are much smaller than the DC brushless or AC motors commonly in use. Another important advantage, for the present application, of synchronous motors is its constant speed feature. This motor is stable only when operating at synchronous speed corresponding to the frequency of the applied AC power.In fields wherein a synchronous motor shaft must be driven with substantially constant rotational velocity, it is imperative that the frequency of the AC square wave applied to the motor is stable over the short and long terms. In accordance with the teachings of the present invention, an AC synchronous motor, preferably of the hysteresis type, it utilized in a belt driven floppy disk drive system thereby incorporating the advantages of synchronous motors as set forth hereinabove.

According to the invention in its broadest aspect there is provided a rotating memory drive system comprising a rotating member having information storage means associated therewith, a source of DC voltage, means for converting the DC voltage to an AC voltage of a predetermined frequency, and a synchronous motor driven by the AC voltage, the output shaft of the motor driving the rotating member at a substantially constant rotational speed.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the floppy disk drive system of the present invention; Figure 2 is a top plan view along the line 2-2 of Fig. 1; and Figure 3 is a schematic diagram of the motor control circuit of the present invention.

Fig. 1 is a perspective view of the disk drive 10 of the present invention. Although both hard and floppy disks can be utilized as the magnetic recording media, the present invention is preferably utilized to drive floppy disks (or diskettes). A slot, or opening 12, is provided so that the floppy disk can be inserted into the disk drive 10 and positioned onto the disk drive spindle therein.

Fig. 2 is a top plan view along the line 2-2 of Fig. 1 illustrating the main components of the disk drive of the present invention. In particular, a floppy disk 1 4 is shown positioned on drive spindle 16. Magnetic readwrite heads 1 8 are shown positioned in operative relationship with and above the disk 14.

The output shaft (not shown) of an AC synchronous motor 1 9 drives the spindle 1 6 via a belt (not shown) in the standard manner. An AC voltage input 22 is provided to drive motor 20, as will be explained hereinafter with reference to Fig. 3, and a motor capacitor 24 is also provided. The drive electronics printed circuit board (not shown) is mounted in the lower portion of the disk drive system 10. As set forth hereinabove, the important feature of the present invention is the use of an AC synchronous motor 1 9 to drive spindle 1 6 via a drive belt. Although a hysteresis synchronous motor is preferred (such as the Model No. HS-5741, manufactured by Shinano Kenshi, Chiisagata-Gun, Nagano-Ken, Japan, available from C.B.King Associates, Santa Clara, California), reluctance synchronous and permanent magnet type AC synchronous motors could be utilized although they have a lower power efficiency.

The AC synchronous motor 1 9 provides an additional advantage in that its smaller physical size allows it to be positioned away from the area of disk spindle 1 6 thereby minimizing the effect of spurious magnetic fields generated by motor 1 9 on disk 14 and heads 18. These fields would otherwise affect data reliability since the square wave AC signal used to drive the synchronous motor 1 9 of the present invention normally generates greater spurious magnetic fields than the sine wave AC signal utilized to drive prior art AC spindle drive motors.

Fig. 3 is the schematic diagram of the motor control drive circuit for the DC, 50 Hz hysteresis synchronous motor 1 9.

In essence, the DC motor drive circuit is powered by 24 volts from source 20 through a parallel connection of capacitative filters C9, C10 and C11 and supplies square wave voltages to the AC synchronous motor 10 via the circuit to be described. The design approach is usable for voltages other than 24 volts and the square-wave frequency may be other than 50Hz.

The drive motor frequency is crystal-controlled, having excellent short-term and longterm frequency stability, while eliminating the need for any ajustments or feedback from motor 19. The crystal oscillator/divider circuit uses an inexpensive TV colour-burst crystal 22 which is divided down to 100 Hz pulses using integrated circuit U2. Since the U2-100 Hz pulses are not the required 50% duty cycle, integrated circuit U3 divides by two and produces square waves at the desired 50 Hz frequency at its output.

Integrated circuit U5 of which (four are shown) is a delay circuit that delays the turnon edges of the 50 Hz and 50 Hz-inverted signals at the output of U3. Since the transistors Q1, Q2, Q3 and Q4 turn off slower than they turn on, it is necessary to delay the turnon signals to prevent shorting out the 24V supply 20. This momentary short across the 24V supply 20, if allowed to occur, would cause large fast current surges or spikes which would create magnetic fields that could affect the magnetic leads and induce currents and voltages into the transistors, both factors degrading system performance. Pin 6 of U5 drives transistors Q3 and Q2 through the buffer inverters U1. Similarly, U5 pin 8 drives Q1 and Q4 through buffer drives U1. The amount of turn-on delay is controlled by R7, C7 and R9, C8. For the transistors used, the amount of turn-on delay is approximately 20 ysec.

When transistors Q1 and Q4 are on, current flows from the 24 volt supply 20, through Q4 through the motor 1 9 (from pin 4 to pin 3) then returns to the power supply return through Q1. Q1 and Q4 are on approximately 10 milliseconds or one-half of the 50 Hz cycle. Then Q1 and Q4 turn off for approximately 20 microseconds before Q2 and Q3 turn on.

When Q2 and Q3 turn on, 24 volt supply current flows through Q3 and into the motor 10 (from pin 3 to pin 4) and returns to the power supply through Q2.

The configuration of Q1-Q4 and motor 10 is commonly referred to as an H-bridge and has the effect of supplying twice the supply voltage to the motor 1 9 while keeping the current drawn from the power supply relatively constant.

Integrated circuit U4 is a 3-terminal voltage regulator. It supplies the necessary 5 volts for the components shown.

Integrated circuits U1, U2, U3, U4 and U5 are available from National Semiconductor, Inc., Santa Clara, California, the model numbers being 7406, MM5369EST, 74LS74, 78L05, 74LS1 32, respectively. Transistors Q1 and Q2 are 2N6386 and Q3 and Q4 are 8203's, both types available from RCA Corporation, Somerville, New Jersey. Typical circuit values are as follows (all resistors are in ohms, all capacitors are in microfarads): R 1= 1K R 2= 4.7K R 3= 4.7K R 4= 4.7K R 5= 4.7K R 6= 4.7K R 7=13.3K R 8= 4.7K R 9=13.3K R10= 1 R11 = 20M R12 = 270 R13= 4.7K R14= 4.7L R15= 4.7K R16= 4.7K C 1=01 C 2=.01 C 3=.01 C 4 = 30 pf C 5 = 30 pf C 6=.47 C 7=1 C 8=1 C 9=1000 C10= 1000 C11 = 1000

Claims (7)

1. A rotating memory drive system comprising a rotating member having information storage means associated therewith, a source of DC voltage, means for converting the DC voltage to an AC voltage of a predetermined frequency, and a synchronous motor driven by the AC voltage, the output shaft of the motor driving the rotating member at a substantially constant rotational speed.

2. A drive system as claimed in claim 1 wherein the sychronous motor comprises a hysteresis synchronous motor.

3. A drive system as claimed in claim 2 wherein the rotating member comprises of floppy disk.

4. A drive system as claimed in claim 1 wherein the converting means comprises a crystai-controlled oscillator.

5. A drive system as claimed in claim 4 wherein the converting means further comprises a time delay circuit coupled between the crystal-controlled oscillator and the DC voltage source to prevent current surges at the input line of the DC voltage source.

6. A drive system as claimed in claim 1 wherein the disk drive system comprises a spindle and read-write leads adjacent to the spindle, the motor output shaft driving the spindle, the rotating member being operatively positioned with respect to the spindle away from the area of the spindle thereby eliminating the effect of the magnetic fields produced by the motor on the rotating member and read-write heads.

7. A rotating memory drive system substantially as described with reference to the accompanying drawings.