JPH0833997B2 - Piezoelectric element disconnection detection circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a disconnection detection circuit for a piezoelectric element, and more specifically, in a surface inspection device for a magnetic disk substrate,
The present invention relates to a piezoelectric element disconnection detection circuit that can easily detect a disconnection of a sensor that detects a protrusion on a surface.

[Prior Art] There are various types of discs used for recording and reading information, such as hard magnetic discs and optical discs. The disc substrates that are these substrates have a high degree of flatness on their surfaces. As required, surface accuracy inspection, so-called surface roughness inspection, is performed.

For example, in order to detect the surface accuracy of the magnetic disk substrate, that is, to inspect the height and the number of protrusions on the surface, the magnetic disk substrate chucked by the spindle is rotated at a constant speed, and the resulting air flow is generated. Thus, the head is levitated by the presence or absence of contact between the head and the protrusion on the plane of the magnetic disk substrate. In this case, a piezoelectric sensor is generally used as the head for detecting the contact between the protrusion and the head.

[Problems to be Solved] In such a conventional disk surface inspection method, if the piezoelectric element for detecting the contact is broken, the inspection becomes impossible, and further, the head (sensor) is broken. Is
Since there is no protrusion on the disk substrate to be measured, it cannot be determined how effectively the inspection is performed, which is a problem.

Therefore, it is necessary to check whether the head is broken or not, but it is inefficient to perform the inspection after checking each time.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a disconnection detection circuit for a piezoelectric element, which can easily detect the disconnection in a head or the like using the piezoelectric element.

[Means for Solving Problems] In order to achieve such an object, the configuration of the disconnection detection circuit for a piezoelectric element according to the present invention includes an amplifier circuit for amplifying a noise component of the piezoelectric element and an output of the amplifier circuit. A rectifier circuit for rectifying and a comparator circuit for comparing an output signal of the rectifier circuit or a signal obtained by amplifying the output signal with a reference value are detected, and disconnection of the piezoelectric element is detected when the rectified value of the noise component is a predetermined value or more. It is a thing.

[Operation] Since the disconnection state of the piezoelectric element can be determined by the noise in this way, when the piezoelectric element is used as a sensor or the like, it is possible to constantly monitor whether or not the sensor is valid. Therefore, for example, in the case where the disconnection has a great influence on the inspection, such as the head of the surface inspection device for the disk substrate, the validity / invalidity of the sensor can be grasped in real time.
Efficient measurement is possible.

[Embodiment] An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram centering on a contact detection circuit when a disconnection detection circuit for a piezoelectric element according to the present invention is applied to a head of a magnetic disk surface inspection apparatus, and FIG. 2 is the entire magnetic disk surface inspection apparatus. It is a typical block diagram.

In FIG. 2, reference numeral 1 denotes a magnetic disk substrate (hereinafter referred to as a measured disk) to be tested, which is chucked by a spindle 2a of a spindle motor 2. Reference numeral 3 denotes a head for detecting contact by a sensor of a piezoelectric element, which is arranged above the surface of the measured disk 1 so as to face the surface, and air generated therein as the measured disk 1 rotates. Surface up.

The head 3 is supported by the carriage 4 and reciprocates in the radial direction on the surface of the measured disk 1 in response to the reciprocating movement of the carriage 4. The carriage 4 is moved by the carriage motor 5, and the carriage 4 is pitch-fed. The carriage motor 5 is a stepping motor and rotates a predetermined amount in a direction selected according to a drive signal from the carriage drive circuit 6. Reference numeral 7 denotes a spindle drive circuit which receives a control signal for designating the number of revolutions of the measured disk 1 from the surface inspection processing device 10.

Here, in the rotation control state of the measured disk 1,
The output of the head 3 is input to the contact detection circuit 8 to detect the level of the input signal to detect the contact state, and the detection signal is sent to the surface inspection processing circuit 10 as surface inspection data. The surface inspection processing circuit 10 is a microprocessor 10a.
And interface with memory 10b and D / A converter 1
0c, etc., receives a signal indicating the inspection condition from the keyboard 11 and activates a predetermined program on the memory 10b to execute the surface inspection process. Then, a control signal designating the number of revolutions is sent to the spindle drive circuit 7 via the interface 10c.

Further, the surface inspection processing circuit 10 sends a carriage drive signal corresponding to the operating condition of the carriage to the carriage drive circuit 6.
And the position of the head 3 is sequentially fed by pitch. Then, the contact signal detected by the head 3 is obtained from the contact detection circuit 10, and the presence or absence of contact is stored in the memory 10b by a flag or the like together with the position information corresponding to the position on the measured disk 1 at the currently designated height. To go.

As a result, the surface inspection data of the measured disk 1 is obtained.

Reference numeral 9 denotes a head disconnection detection circuit, which receives a signal from the head 3, detects a head disconnection, and sends the signal to the surface inspection processing apparatus 10. Upon receiving the disconnection detection signal from the head disconnection detection circuit 8, the surface inspection processing device 10 accepts it as an interrupt signal, activates the disconnection processing program, and starts disconnection processing.

As the disconnection treatment, an alarm is displayed on a display (not shown) connected to the surface treatment device 10,
After finishing the surface inspection, the head replacement instruction is displayed.

As shown in FIG. 1, the head disconnection detection circuit 9 includes an amplifier 91 whose input side is connected to the head 3, an average value voltage output circuit 92 which receives its output, and a comparison which receives the output of this average value voltage output circuit 92. It is composed of a comparator 93 as a circuit, and generates a disconnection detection signal at the output of the comparator 93. The reference voltage of the comparator 93 is supplied by the potentiometer 94.

Here, the average value voltage output circuit 92 is composed of a voltage doubler rectifier circuit and an operational amplifier that amplifies a rectified signal, and is a circuit that rectifies a noise signal and generates its average value (rms).

The equivalent circuit of the piezoelectric element of the head 3 is shown as 90 in FIG. 1, and is composed of a capacitance Ca, a resistance R, and a stray capacitance Cs generated by wiring or the like. Here, as the capacitance Ca, about 400 pF to 500 pF is the capacitance of the head for surface inspection, and the value of the resistance R is about 100 kΩ to 150 kΩ. The stray capacitance Cs is about 25PF.

Here, the value of resistance noise due to thermal disturbance generated in the input-added portion is calculated by the following equation.

However, K is the Boltzmann constant, T is the absolute temperature, B is the bandwidth, R is the resistance value, and C is the total capacitance.

 The noise generated in the amplifier 91 is calculated by the following equation.

However, en is the noise value of the input transistor noise resistance of the amplifier.

From the equation, the noise value appearing as the input of the amplifier 91 is Here, if the amplification factor of the amplifier 91 is about 56 dB, the noise value EOUT generated as the output of the amplifier 91 is EOUT = En × 630.

Therefore, when we examine the concrete numerical values according to, it becomes as follows.

K = 1.38 × 10 ^-23 , T = 300 ° K B = 300kHz, Cs = 25 × 10 ^-12 F Ca = 450 × 10 ^-12 F, R = 120 kΩ en = 4 × 10 ^-9 V Here, head 3 When the line is disconnected, the load on the input side of the amplifier 91 is only the stray capacitance Cs in the equivalent circuit 90 in FIG.

Under such conditions, when actually measured,
Following the formula and comparing the calculated theoretical values, the following table is obtained.

However, the unitless value is μV, and the EOUT meter shows Eo
It is the calculated value of ut.

From this table, it can be determined whether or not the head 3 is in the disconnection state by setting the detection reference level at the intermediate level between the actually measured value and the calculated value.

Therefore, if the value of the potentiometer 94, which is the reference value of the comparator, is set in the range of, for example, 4.0 mV to 5.5 mV, it becomes possible to detect the disconnection state of the head 3.

Note that the head 3 generates a vibration signal similar to noise even when it comes into contact with a protrusion, and therefore, if there is a contact detection signal from the contact detection circuit 8 among the disconnection detection signals of the comparator 93, it is invalidated. Should be processed as follows.
Such an invalid circuit may be provided inside the head disconnection detection circuit 9 as a circuit that receives a contact detection signal from the contact detection circuit 8 and blocks output, or may be determined by the surface inspection processing device 10 as an invalid circuit. Good.

As described above, in the embodiments, the description is centered on the surface inspection of the magnetic disk substrate, but the present invention can be applied not only to optical disk substrates, but also to disconnection detection circuits for various disk surface inspections. The present invention can be applied to other general piezoelectric element disconnection detection.

[Effects of the Invention] As can be understood from the above description, in the present invention, since the disconnection state of the piezoelectric element can be determined by noise, whether the sensor is always effective when the piezoelectric element is used as a sensor or the like. It will be possible to monitor whether or not. Therefore, for example, in the case where the disconnection has a large influence on the inspection, such as the head of a disk substrate surface inspection device, the validity / invalidity of the sensor can be grasped in real time, and efficient measurement is possible. Become.

[Brief description of drawings]

FIG. 1 is a block diagram centering on a contact detection circuit when a disconnection detection circuit for a piezoelectric element according to the present invention is applied to a head of a magnetic disk surface inspection apparatus, and FIG. 2 is the entire magnetic disk surface inspection apparatus. It is a typical block diagram. 1 ... Disk to be measured, 2 ... Spindle motor, 2a ... Spindle, 3 ... Head, 4 ... Carriage, 5 ... Carriage motor, 6 ... Carriage drive circuit, 7 ... Spindle drive circuit, 8 ... Contact detection circuit, 9 ... Head disconnection Detection circuit, 10
… Surface inspection processing circuit, 10a… Microprocessor, 10b…
Memory, 10c ... Interface, 11 ... Keyboard, 90 ...
Head equivalent circuit, 91 ... Amplifier, 92 ... Average value voltage output circuit, 93 ... Comparator.

Claims (2)

[Claims] 1. An amplifier circuit for amplifying a noise component of a piezoelectric element, a rectifier circuit for rectifying an output of the amplifier circuit, and a comparison circuit for comparing an output signal of the rectifier circuit or an amplified signal thereof with a reference value. A disconnection detection circuit for a piezoelectric element, comprising: detecting a disconnection of the piezoelectric element when a rectified value of a noise component is a predetermined value or more. 2. The piezoelectric element is mounted on a head of a surface inspection device as a sensor, and the rectifier circuit is a voltage doubler rectifier circuit,
The disconnection detection circuit for a piezoelectric element according to claim 1, wherein the rectified value is amplified by an operational amplifier and supplied to a comparison circuit.