Patent Application
20190131752
The present invention relates to a technique for welding conductors to each other by ultrasonic vibration energy.
Ultrasonic welding methods of welding one conductor and the other conductor coated with synthetic resins have been proposed (for example, see Patent Literatures 1 and 2). According to the ultrasonic welding methods, at least the synthetic resin with which the one conductor is coated is first melt by the ultrasonic vibration energy of a horn with a welding target interposed between the horn and an anvil, and is removed from between the both conductors. Subsequently, the both conductors are welded to each other.
A method of realizing ultrasonic welding while preventing a variation in a welding strength of the both conductors caused due to a variation in the ultrasonic vibration energy has been proposed (for example, see Patent Literature 3). According to the method, a product of a voltage applied to a vibration element vibrating the horn and a current flowing in the vibration element is calculated as a work rate given to a welding target via the horn. Then, when a rate of change in the work rate becomes equal to or less than a first predetermined value, and subsequently becomes equal to or greater than a second predetermined value greater than the first predetermined value, the coating is determined to be removed from between the conductors.
Patent Literature 1: Japanese Patent Application Laid-Open No. 2000-263248
Patent Literature 2: Japanese Patent Application Laid-Open No. 2006-024590
Patent Literature 3: Japanese Patent No. 4456640
However, since there is a transitional period in which conductor welding starts and the coating removal further progresses, there is a possibility that it is difficult to determine whether the removing of the coating is completed based on a change in the work rate. Therefore, there is a possibility that, for example, the conductor is damaged due to excessive ultrasonic vibration energy in addition to the possibility that the welding strength of the conductor is insufficient due to small ultrasonic vibration energy.
Accordingly, an object of the invention is to provide a device and the like capable of improving quality of welding by improving estimation precision of coating removal completion of conductors which are ultrasonic welding targets.
According to an aspect of the invention, there is provided an ultrasonic welding device including: a horn that is vibrated by a piezoelectric element; an anvil that is disposed to face the horn; and a control device. A synthetic resin is melted to be removed from between one conductor and another conductor by displacing the horn in a superimposing direction of the one conductor and the other conductor while ultrasonically vibrating the horn in a state in which the one conductor and the other conductor superimposed via the synthetic resin are interposed by the horn and the anvil, and the one conductor and the other conductor are welded.
In the ultrasonic welding device according to the aspect of the invention, the control device includes a measurement element that measures, as a reference displacement amount, a displacement amount of the horn during a reference period which is at least a partial period of a period from the state in which the one conductor and the other conductor superimposed via the synthetic resin are interposed by the horn and the anvil, through a first stable state in which a displacement speed of the horn is stable in a first speed zone in a course in which the displacement speed increases, until a second stable state in which the displacement speed is stable in a second speed zone of a higher speed zone than the first speed zone, and an adjustment element that adjusts ultrasonic vibration energy of the horn so that the ultrasonic vibration energy of the horn decreases continuously or step by step during a period following the reference period as the reference displacement amount measured by the measurement element increases.
The “first stable state” is a state in which the displacement speed of the horn is stable in the first speed zone and corresponds to a state before start of or an early stage of melting and removal of the synthetic resin between the both conductors by the ultrasonic vibration energy of the horn. The “second stable state” is a state in which the displacement speed of the horn is stable in the second speed zone of a higher speed zone than the first speed zone and is equivalent to an ending stage or a state after end of the melting and removal of the synthetic resin between the both conductors.
The displacement amount of the horn during the period from start of the displacement of the horn for the welding of the one conductor and the other conductor, through the first stable state in the course in which the displacement speed increases to the second stable state indicates a progress situation of the melting and removal of the synthetic resin between the both conductors. Therefore, when the magnitude of the ultrasonic vibration energy of the horn is controlled based on the magnitude of the displacement amount (the reference displacement amount) of the horn during at least a partial period (the reference period) of the period, the magnitude of energy converted to the welding of both conductors is appropriately adjusted from the viewpoint of realizing sufficient welding strength by the welding of the both conductors.
(Configuration)
An ultrasonic welding device according to an embodiment of the invention, as illustrated in
The control device 20 includes a computer (which includes an arithmetic processing unit (CPU), a memory (a storage device) such as a ROM or a RAM, an I/O circuit, and the like). The control device 20 controls an operation of each of the lifting driving device 111 and the piezoelectric element 112. The control device 20 includes a measurement element 21 and an adjustment element 22. The elements 21 and 22 each include an arithmetic processing unit that reads a program and data necessary from the storage device and performs an arithmetic process to be described below according to the program and the data.
As welding targets by the ultrasonic welding device, for example, a first conductor C1 (one conductor) formed of metal for a flexible flat cable (FFC) and a second conductor C2 (the other conductor) formed of metal for a printed circuit board (PCB) are adopted. The FFC includes an insulating coating C0 formed of a synthetic resin that covers the first conductor C1 in addition to the first conductor C1. The PBC includes a board supporting the second conductor C2.
Only the single first conductor C1 is illustrated to facilitate the drawings, but the plurality of first conductors C1 arranged in parallel in the horizontal direction and extending in the vertical direction in the FFC is covered with the insulating coating C0 so that the first conductors C1 are electrically isolated from each other. Similarly, only the single second conductor C2 is illustrated, but the plurality of second conductors C2 is installed on a board in the PCB.
In addition to the conductors included in the FFC and the PCB, conductors included in the plurality of FFCs or conductors included in the FFC and a flexible printed circuit (FPC) may be considered to be welding targets.
(Method of Adjusting Ultrasonic Energy (First Embodiment))
An ultrasonic welding method will be described as a first embodiment of the invention realized by the ultrasonic welding device that has the foregoing configuration. First, as illustrated in
From this state, the horn 11 is displaced to approach the anvil 12 by the lifting driving device 111, and thus by applying a load in the vertical direction to the FFC and the PCB and by applying an alternating-current voltage with a high frequency to the piezoelectric element 112 to ultrasonically vibrate the horn 11 (in the horizontal direction in the drawing), the FFC and the PCB (or the first conductor C1 and the second conductor C2) start to be welded.
(Time Change Form of Displacement Amount of Horn)
Until welding of the first conductor C1 and the second conductor C2 is completed, a displacement amount Z of the horn 11 is changed in accordance with a function Z(t) of a time t simplified in, for example,
That is, the displacement amount Z of the horn 11 first increases at a relatively high speed during the early term of a first period [t11, t12], and subsequently increases at a relatively low speed. A “first stable state” in which a displacement speed v of the horn 11 is stable in a first speed zone during the late term (or the middle term and the late term) of the first period [t11, t12] is realized. The first speed zone is a speed zone that is defined by a lower limit and an upper limit of a slope of a curve line Z=Z(t) in the late term of the first period. A time change form of the displacement amount Z of the horn 11 during the first period [t11, t12] is in conformity with Relational Expression (1) below.
ε1(t)=(σ0/E){1−exp(−(t)/(η/E))} (1)
Relational Expression (1) approximately expresses a strain amount ε1(t) (equivalent to the displacement amount Z of the horn 11) of the insulating coating C0 formed of a synthetic resin when a constant external force σ0 is applied at time t=−0 in accordance with the Kelvin-Voigt model. In this model, elasticity and viscosity characteristics of the synthetic resin are expressed by a parallel spring (elastic coefficient: E) and a damper (attenuation coefficient: η).
In
The temperature of the FFC and the PCB at spots interposed between the horn 11 and the anvil 12 are locally increased by the ultrasonic vibration energy of the horn 11, and the insulating coating C0 of the FFC is locally melted. The melted insulating coating C0 (the synthetic resin) is gradually removed from between the horn 11 and the anvil 12 because of a load of the horn 11 and the anvil 12 in the vertical direction. At this time, the insulating coating C0 between the first conductor C1 and the second conductor C2 is also melted and is gradually removed from between the first conductor C1 and the second conductor C2. As illustrated in
Subsequently, the second conductor C2 abuts on the first conductor C1 while the second conductor C2 is plastically deformed. Frictional heat occurs in the abutting spots due to the ultrasonic vibration energy of the horn 11, an oxide film generated on the metal surface of each of the first conductor C1 and the second conductor C2 is removed, and an active surface (also referred to as a clean surface) is exposed to cause welding reaction (also referred to as solid phase welding).
When the solid phase welding reaction between the first conductor C1 and the second conductor C2 is in progress, a “second stable state” in which the displacement speed v of the horn 11 is stable in a second speed zone during the second period [t21, t22] is realized. The second speed zone is a speed zone that is defined by a lower limit and an upper limit of a slope of a curve line Z=Z(t) during the second period. A time change form of the displacement amount Z of the horn 11 during the second period [t21, t22] is consistent with Relational Expression (2) below.
ε2(t)=A·D·(σ0/G)n×t (2)
Relational Expression (2) approximately expresses a strain amount ε2(t) in a transient creep region of the first conductor C1 and the second conductor C2 formed of metal using a material constant A, a diffusion coefficient D, and a coefficient G of the metal.
In
(Method of Adjusting Ultrasonic Energy)
The measurement element 21 of the control device 20 measures a displacement amount Z (t12)−Z(t11) of the horn 11 during the “first period” serving as a “reference period” as a reference displacement amount ΔZ based on an output signal from a displacement amount sensor (not illustrated) according to the displacement amount Z of the horn 11 (STEP 102 of
It is determined whether the reference displacement amount ΔZ of the horn 11 is equal to or less than at (STEP 104 of
When the reference displacement amount ΔZ is determined to be equal to or less than at (YES in STEP 104 of
Then, after the welding reaction between the first conductor C1 and the second conductor C2 is completed, the horn 11 returns to the original position and the ultrasonic vibration is also stopped.
(Ultrasonic Welding Method (Second Embodiment))
An ultrasonic welding method will be described as a second embodiment of the invention realized by the ultrasonic welding device that has the foregoing configuration. Since the second embodiment is common to the first embodiment except for a method of controlling ultrasonic vibration energy, the common factors will not be described.
A displacement amount Z(t21)−Z(t11) of the horn 11 during a “first period” serving as a “reference period” and a “transition period” is measured as a reference displacement amount ΔZ (STEP 202 of
It is determined whether the reference displacement amount ΔZ of the horn 11 is equal to or less than a2 (STEP 204 of
When the reference displacement amount ΔZ is determined to be equal to or less than a2 (YES in STEP 204 of
Then, after the welding reaction between the first conductor C1 and the second conductor C2 is completed, the horn 11 returns to the original position and the ultrasonic vibration is also stopped.
(Ultrasonic Welding Method (Third Embodiment))
An ultrasonic welding method will be described as a third embodiment of the invention realized by the ultrasonic welding device that has the foregoing configuration. Since the third embodiment is common to the first embodiment except for a method of controlling ultrasonic vibration energy, the common factors will not be described.
A displacement amount of the horn 11 during a “reference period” is measured as a reference displacement amount ΔZ (STEP 302 of
It is determined whether the reference displacement amount ΔZ of the horn 11 is equal to or less than a3 (STEP 304 of
When the reference displacement amount ΔZ is determined to be equal to or less than a3 (YES in STEP 304 of
Then, after the welding reaction between the first conductor C1 and the second conductor C2 is completed, the horn 11 returns to the original position and the ultrasonic vibration is also stopped.
A displacement amount of the horn during a period from the state in which the FFC and the PCB are vertically interposed between the horn 11 and the anvil 12 through the first stable state in which the displacement speed v of the horn 11 increases (a state in which a displacement acceleration α=dv/dt=d2Z/dt2 is equal to or greater than 0) to the second stable state indicates a progress situation of melting and removal of the synthetic resin included in the insulating coating C0 between the both conductors C1 and C2. The fact that the displacement amount (the reference displacement amount ΔZ) of the horn 11 during at least a partial period (reference period) of the period is large suggests that elasticity and viscosity of the synthetic resin included in the insulating coating C0 during the period is low or the temperature is high and thus the ultrasonic vibration energy E of the horn 11 is relatively high.
Therefore, by performing control such that the ultrasonic vibration energy E of the horn 11 is relatively low when the reference displacement amount ΔZ is large, the excessive ultrasonic vibration energy E at the time of welding the both conductors C1 and C2 is prevented. Therefore, it is possible to reliably realize sufficient welding strength between the conductors C1 and C2. In contrast, by performing control such that the ultrasonic vibration energy E of the horn 11 is relatively high when the reference displacement amount ΔZ is small, the small ultrasonic vibration energy E at the time of welding the both conductors C1 and C2 is prevented. Therefore, it is possible to reliably realize sufficient welding strength between the conductors C1 and C2.
In the first to third embodiments, the ultrasonic vibration energy E is adjusted at three stages according to the magnitude of the reference displacement amount ΔZ. However, in another embodiment, the ultrasonic vibration energy E may be adjusted at two stages or at multiple stages equal to or greater than four stages according to the magnitude of the reference displacement amount ΔZ or may be adjusted continuously.
As the reference period, a period of another form such as, for example, a period [t11, t20] or a period [t12, t20] may be adopted as long as the reference period is at least a partial period of a period from a displacement starting time t=t11 of the horn 11 to an ending time t=t21 of the transition period from the first stable state to the second stable state.
In the first to third embodiments, the reference period may be set to start after the displacement amount Z from the displacement starting time t=t11 of the horn 11 reaches a predetermined amount Z0. In this case, the reference displacement amount ΔZ in each of the first to third embodiments may be substituted with ΔZ−Z0 and the ultrasonic vibration energy E may be adjusted according to the magnitude of the reference displacement amount after the substitution, as described above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-055915 | Mar 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/007658 | 2/28/2017 | WO | 00 |
