1. Field of the Invention
The present invention relates to a vibration measurement method and apparatus and in particular, to a method and an apparatus for identifying a vibration state of an object to be measured, i.e., a vibrating object by using the Doppler effect of laser light (beam).
The present invention can be applied to experiments for automobile production. More specifically, the present invention can be applied engine vibration analysis, body vibration transfer analysis, noise in the body, muffler vibration analysis, and the like. Since the vibration measurement apparatus according to the present invention is non-contact type capable of accurately measuring a small region, the apparatus can be preferably applied for detecting a tool breakage such as a drill. As will be detailed later, the present invention can be applied to a junction failure in a production technology. Furthermore, the present invention can be applied to a plant vibration using a motor, and maintenance of a water pipe and gas pipe for detecting leakage. Moreover, the present invention can be applied even to agriculture. A large fruit such as a watermelon can be knocked, so that resultant sound is detected to determine sweetness of the watermelon without cutting the watermelon. Hereinafter, "the object to be measured" includes an object, from an engine to watermelon, whose vibration is detected by the present invention.
2. Description of the Related Art
Conventionally, for analyzing a vibration state of an object to be measured, an acceleration pickup is attached to the object, which is knocked to vibrate, so as to analyze the acceleration pickup. However, in this case the acceleration pickup is in contact with the object to be measured. Accordingly, it is impossible to measure vibration if the object to be measured is very small or at a high temperature. Moreover, the contact type measurement with a pickup affects the vibration measurement.
As a non-contact type vibration measurement method, there is an apparatus for measuring vibration using a laser with the Doppler effect. For example, Japanese Patent Publication (unexamined) 10-9943 filed by the same applicant as the present invention discloses a vibration measurement method applying a laser light and the reflected light and oscillating light are mixed so as to detect Doppler frequency contained in the reflected light, thus enabling to measure the vibration frequency. This will be referred to as a self-mixing method.
Excluding the self-mixing type, the conventional vibration measurement apparatus mix the oscillating light with the reflected light externally using an expensive and accurate optical element. Accordingly, a space is required for allocating the element. This results in an expensive and heavy apparatus. In contrast to this, the self-mixing type, oscillation light is mixed with the reflected light using a laser resonator (laser diode). Thus, the self-mixing type enables to measure a vibration frequency at a low cost, with a small-size and small-weight apparatus without requiring the expensive optical system used in the non self-mixing type.
As a method for detecting a vibration information from a resultant beat wave generated in the self-mixing type, there are some methods: a method to obtain a vibration information from counting the beat waves and converting it into a vibration displacement; a method for differentiating a beat wave to obtain a vibration speed information and identifying a turning point of the vibrating plane to obtain the direction of the vibration displacement; and others. These methods count beat waves during the vibration plane advance direction is changed (turned).
However, the aforementioned methods require a beat wave extraction and a complicated calculation procedure. Furthermore, in the method counting the beat waves, the object displacement is determined by .lambda./2 of the laser light and cannot detect the vibration state changing by less than .lambda./2.
Moreover, the conventional method requires a number of calculation processes to identify the vibration state and it is difficult to assure response speed for real time measurement.
Next, explanation will be given on applications of the conventional example. A wire bonding apparatus for connecting a silicon chip and a lead frame using weight, heat, and supersonic vibration of about 60 kHz. The bonding apparatus repeated moves so that wire bonding is performed on a number of chips on a fixed table.
Conventionally, the bonding quality test has been performed by indirect inspection for electric conductivity and pulling test as well as the ultrasonic wave oscillator impedance change, and a fine change of pressurizing state. For example, there is a method using a non-contact type laser oscillation meter such as argon and helium-neon for use apart from the bonding apparatus.
However, in a conventional example for checking the wire bonding, there is a case when checking by current application may be impossible because of the IC internal circuit configuration. Moreover, the pulling test may break the bonding and is performed as a sampling inspection after bonding is complete. Accordingly, it is impossible to immediately stop the wire bonding apparatus when a junction failure is detected.
In a case of the impedance change, vibration state change of a tip (horn) of a resonator is detected at the root of the horn and accordingly, it is impossible to accurately detect the vibration state change due to the junction state change. Moreover, in pickup of pressurizing state, a piezoelectric element set on the fixed table of the silicon chips cannot accurately detect the vibration state of the horn. In a case of non-contact type laser vibration meter using argon or helium-neon, it is difficult to fix the laser head because of its large size and weight and cannot follow the bonding apparatus during operation.
Thus, in the conventional junction inspection systems for the wire bonding apparatus cannot move together with the wire bonding apparatus, i.e., cannot inspect at real time.