JPS6153944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oscillation circuit for ultrasonic plastic welding.

Conventional ultrasonic oscillation circuits used in ultrasonic welding equipment that weld plastic molded products using ultrasonic vibration are designed to supply a certain voltage and current to the vibrator in accordance with the load impedance during plastic welding. It had been. In addition, some models have a constant amplitude control function added to prevent the vibration of the vibrator and drop in amplitude during welding, but in the conventional type, the vibrator maintains a predetermined amplitude immediately after welding starts, as shown in Figure 1. It was supposed to be driven by the level.

On the other hand, the workpiece to be welded is usually provided with a rib-like protrusion on one side of the welding part in order to efficiently start welding, and the welding process gradually melts from this protrusion.
The structure is such that this rib completely melts when welding is finished, but this rib usually has a triangular cross section, and since it gradually melts from its apex, contact with the welding material is almost a linear contact at the beginning of welding, and it gradually melts. surface contact, and the area increases rapidly. In other words, even though the welding surface fluctuates considerably over time, the welding equipment is driven with a nearly constant amplitude, so the ultrasonic energy is not absorbed near the ribs immediately after welding starts, and the entire welded object is strongly It will be vibrated,
For this reason, some parts of the welded product may break at weak points, resulting in cracks, deformation, and melting in areas other than the ribs. To prevent this kind of situation, gradually increase the voltage applied to the vibrator.
It is possible to apply a low voltage at the beginning and then apply a higher voltage as the welding progresses.
Various devices have been proposed, but none have yet been effective.

An example of a conventionally used oscillation circuit is shown in the second example.
To explain based on the diagram, _A1 is the excitation stage amplifier,
A ₂ is a voltage amplifier that amplifies the output of this excitation stage amplifier A ₁ , and F ₁ is an output circuit connected to this power amplifier and sends the output to the ultrasonic transducer T ₁ . Oscillation is performed by feeding back the output signal from the output circuit _F1 to the excitation stage amplifier _A1 . Further, M ₀ is a power supply circuit that rectifies the alternating current supplied from the alternating current power source and supplies direct current to the excitation stage amplifier A ₁ .

This power supply circuit M ₀ was configured as follows. That is, the control output of the AC control section _M1 using a triax or thyristor is supplied to the power amplifier A2 via the rectifier circuit _M2 , and the control output of the AC control section _M1 is supplied to the power amplifier _A2 via the rectifier circuit M2. An ignition control oscillation circuit _M3 is connected to the gate via a switch St, and a power adjustment variable resistor _VR1 for adjusting the ignition time is further connected to this ignition control oscillation circuit _M3 . By adjusting this VR ₁ , the firing time of the firing control oscillation circuit _M3 is changed, and the conduction time of _M1 is changed.

According to this conventional oscillation circuit _M0 , when the switch St is turned on, the voltage _V1 applied to the power amplifier _A2 through the rectifier circuit _M2 is changed to the rectifier circuit _M2.
Although there is some delay due to the internal smoothing circuit, etc., the voltage rises almost instantaneously to a constant voltage, and V ₁ ',
Along with this, the applied voltage _{V 2 of} the ultrasonic oscillator T ₁ also becomes a waveform with a steep rise like V ₂ ', V ₂ '' in Fig. 4, as described above. This caused excessive melting of the welded object, causing cracks, and cracks. Therefore, the output voltage V ₁ of the power supply circuit M ₀ and the voltage applied to the ultrasonic transducer V ₂ are in a proportional relationship, and when the output voltage V ₁ is changed, the voltage applied to the ultrasonic transducer V ₂ changes accordingly. Taking this into consideration, a circuit was also proposed in which the output voltage V ₁ of the power supply circuit M ₀ is increased stepwise as shown in FIG.

In other words, a variable resistor is added to the ignition time control oscillator circuit _M3 .
The collector of transistor Q ₁ is connected through VR ₁ , and the base of transistor Q ₁ is connected to the positive terminal of DC power supply E ₀ through resistor R ₁ , switch S ₂ , and resistor R ₂ . A capacitor C1, one end of which is grounded _, is connected in parallel with this resistor _R1 between the switch _S2 and the resistor _R1 . Then, with the resistor R ₂ and capacitor C ₁ ,
It is designed to form a CR time constant circuit. Therefore, in this oscillation circuit, switch _S2 is turned on.
Then, capacitor C ₁ is first charged by the time constant of R ₂ C ₁ , and as a result, transistor Q ₁ gradually shifts to the ON region as shown in Figure 6, and becomes completely ON at time t ₁ . . In other words, the internal impedance between the collector and emitter from time t ₀ (when switch S ₂ is turned on) to time t ₁ is
This means that the CR curve has changed, and the variable resistance VR ₁
By inserting transistor Q ₁ in series with , the same effect as increasing or decreasing VR ₁ can be obtained. As a result, the output voltage V ₁ has a waveform as shown by the solid line in Figure 3, and the voltage applied to the ultrasonic transducer V ₂
has a waveform as shown by the solid line in FIG. However, even in this circuit, the voltage rises rapidly and is insufficient to prevent over-melting of the welded object at the initial stage of welding.

The present inventor provided two transistors and increased the voltage applied to the ultrasonic transducer in two stages by shifting the conduction timing of these transistors, and by applying low power in the early stage of welding and high power ultrasound energy in the latter stage. We have developed an ultrasonic oscillator circuit for plastic welding which supplies the welding material to the object to be welded, and hereby propose it as the present invention.

The configuration will be explained below based on an embodiment of the present invention shown in FIG.

A ₁ is the excitation stage amplifier, A ₂ is this excitation stage amplifier A ₁
A power amplifier that amplifies the output of , F ₁ is an output circuit that is connected to this power amplifier and sends the output to the ultrasonic transducer T ₁ , and as in the conventional device, this output circuit
Oscillation is performed by feedback of the output signal from _F1 to the excitation stage amplifier _A1 . Further, Ma is a power supply circuit that rectifies the alternating current supplied from the alternating current power source and supplies direct current to the power amplifier _A2 . This power supply circuit Ma is configured as follows.

That is, using a triax or thyristor
The control output of the AC control unit _M1 is supplied to the power amplifier _A2 via the rectifier circuit _M2 ,
Further, a firing control oscillation circuit _M3 is connected to the gate of this AC control section _M1 , and a power adjustment variable resistor _VR1 for adjusting the firing time is connected to this firing control oscillation circuit _M3 . The collectors of a pair of transistors Q ₁ and Q ₂ are connected in parallel to this variable resistor VR ₁ . Note that the collector of the transistor _Q1 is connected to a variable resistor via a resistor _R4 .
It is connected to VR ₁ and its emitter is grounded. The base is also connected to a switch _S2 via a resistor _R1 . This switch _S2 selectively connects to the ground or the DC power supply _E0 ; when it is turned on, the base of the transistor _Q1 and the DC power supply _E0 are connected, and when it is turned off, the base is grounded. It is becoming more and more common. Also, a resistor R ₁ is connected between the DC power source E ₀ and the switch S ₂ , and a capacitor C ₁ is connected between the switch S ₂ and the base of the transistor Q ₁ and grounded in parallel with this base.
is provided, and this capacitor C ₁ and resistor
_R1 forms a CR time constant circuit. At the same time, the base of transistor Q ₂ is connected via resistor R ₁ to switch S ₃ , which selectively connects to ground or to DC power supply E _{0, and there is no connection between DC power supply E 0 and} switch S ₃ . Between the switch S ₂ and the base of the transistor _{Q 1} , there is a capacitor _{C 2} with one end grounded in parallel with the base of the resistor R ₁ .
It forms a time constant circuit. The switch _S3 is turned on and off by a timer B.

Next, to explain the operation of this ultrasonic oscillation circuit,
When the ultrasonic activation switch _S2 is turned on, the transistor _Q1 is gradually turned on with the time constant of _R2 and _C1 , conduction occurs between the emitter and the collector, and current begins to flow. Next, at predetermined intervals, the ultrasonic start switch _S3 is turned on at time _t2 by a command from timer B, and the transistor is gradually turned on with the time constants _R6 and _C2 .
Q ₂ turns on.

As a result, the voltage VCE ₂ becomes t ₀ as shown in FIG.
to _t2 is determined by the operation of transistor _Q1 , and _VCE3 is determined by resistor _R4 . Therefore, when the switch _S3 is turned on at time _t2 due to the operation of the timer B, _VCE2 becomes OV from _t2 to _t4 due to the effect of the transistor _Q2 . As a result, the voltage of _V1 has a waveform as shown in FIG. 9, and the amplitude of the vibrator has a waveform as shown in FIG.

As described above, the ultrasonic oscillator circuit of the present invention can apply voltages to the vibrator by differentiating them into preheating time, welding time, preheating voltage, and welding voltage level by changing the applied voltage, thereby preventing cracks, deformation, etc. It has the excellent effect of preventing failures and efficiently performing precision plastic welding.

[Brief explanation of the drawing]

Figure 1 is a diagram of the amplitude waveform of a vibrator driven by a conventional oscillator, Figure 2 is a block diagram of a conventional oscillation circuit, and Figure 3 is a diagram of a conventional device.
Figure 4 is a voltage waveform diagram of V ₁ , Figure 4 is a voltage waveform diagram of V ₂ , Figure 5 is a block diaphragm of an oscillation circuit using conventional transistors, Figure 6 is the VCE voltage of the transistor used in the device shown in Figure 5. FIG. 7 is a block diagram of the oscillation circuit according to the present invention, FIG. 8 is a voltage waveform diagram of VCE ₂ of transistors Q ₁ and Q ₂ in the device according to the present invention, and FIG. 9 is a voltage waveform of V ₁ thereof. 10 are amplitude waveform diagrams of a vibrator driven by an oscillator.

Claims (1)

[Claims] 1 The voltage supplied to the ultrasonic vibrator is divided into two stages, and the voltage at the start of welding is lower than the second half,
An oscillation circuit for ultrasonic plastic welding characterized by controlling the amplitude of a vibrator by providing an oscillation circuit that switches after a certain period of time and outputs high output in the latter half.