Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-06-14
2001-09-25
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S739000, C029S740000, C029S707000, C029SDIG004, C318S135000, C310S012060, C901S040000, C294S064200, C414S737000, C414S751100, C414S752100
Reexamination Certificate
active
06293006
ABSTRACT:
BACKGROUND
The present invention relates to an electronic component mounting method implemented in an automatic electronic component mounting apparatus.
Electronic component mounting apparatuses have been desired to be operated at a high speed and with high accuracy in recent years. A multi-functional component mounter equipped with a component transfer head movable in X and Y directions by means of an X-Y robot for picking up and mounting electronic components has been accordingly widespread in the market because of the flexibility of component supply modes, the abundance of component types that can be mounted, and high mounting precision due to simplicity of its construction.
At the moment, in an attempt to further accelerate the operation speed and to achieve even higher precision in the electronic component mounting apparatus, there are being developed X-Y robots which employ a linear motor, or component suction nozzles with an upward/downward drive mechanism which can be pressure controlled so as to adjust pressure when mounting components. For high-speed operation of such nozzles, there have been developed an upward/downward drive mechanism having a drive source, such as a rotary motor or air cylinder, and a ball screw or link mechanism combined with such drive source, or a voice coil motor (hereinafter referred to as VCM) having a shaft in the interior thereof, at the lower end of which a nozzle is attached uniformly or in operative connection so that the nozzle is directly driven upwards and downwards at a high speed.
One conventional electronic component mounting apparatus using this VCM will be described with reference to
FIG. 5
showing its system construction and
FIG. 6
which is a flow chart of control actions in the event of an abnormal condition.
In
FIG. 5
,
1
is a nozzle for picking up and mounting electronic components,
2
is a VCM having a shaft
8
for causing the nozzle
1
to move upwards and downwards,
3
is a position detector or a magnet scale for detecting the position of the VCM
2
in upward and downward directions,
4
is a VCM control unit for executing positioning control of the VCM
2
and torque control of same by varying the amount of electric current supplied to the VCM
2
,
5
is an input/output control unit for controlling suction/evacuation of the nozzle
1
and actions of a gripping device,
6
is a gripping device for preventing the fall of the nozzle
1
by holding the shaft
8
, and
7
is a system control unit for sending the positioning control instructions and torque control to the VCM control unit
4
.
Control of the electronic component apparatus described above will be explained with reference to FIG.
5
. VCM
2
is controlled by a servo loop including magnet scale
3
and VCM control unit
4
. In a servo lock state, the gripping device
6
is opened in accordance with the instruction from input/output control unit
5
. When performing picking up and mounting operations of electronic components, the VCM control unit
4
drives the VCM
2
towards a predetermined position in accordance with instructions from system control unit
7
, whereby the positioning of the nozzle
1
is achieved at a high speed.
In case the magnet scale
3
, which performs position detection of the VCM
2
, is disconnected and thereby positioning control by the VCM control unit
4
is impeded, control is effected as follows under order to keep the VCM
2
in control. Referring to
FIG. 6
, when disconnection is detected at step #
1
, the VCM control unit
4
outputs a braking signal to the input/output control unit
5
, upon which the input/output control unit
5
instructs the gripping device
6
to close at step #
2
, and at the same time (at step #
3
), the VCM control unit
4
cuts a drive power supply to the VCM
2
. By the above control, the upper end of the shaft
8
which is driven upwards and downwards within the VCM
2
is grasped by the gripping device
6
, and the nozzle
1
attached at the lower end of the shaft
8
is prevented from falling.
However, in the control method of electronic component mounting apparatus as described above, there exists a time lag between the points when the drive power supply to the VCM
2
is cut and when the gripping device
6
holds the shaft
8
. Since the sliding resistance between the shaft
8
driven upwards and downwards and the gripping device
6
is set as small as possible in this type of electronic component mounting apparatus because of the characteristics of VCM
2
, there is a problem that the nozzle
1
at the lower end of the shaft
8
free-falls during this time lag. This problem occurs whenever the positioning control of the VCM
2
is impeded by any failures such as power outage of the VCM control unit
4
, other than the case where the magnet scale
3
is disconnected.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide an electronic component mounting method by which installing of an electronic component at higher speed can be accomplished and a nozzle can be prevented from falling in the event of failures of the positioning control of a VCM.
To accomplish the above object, the present invention provides an electronic component mounting method implemented in an electronic component mounting apparatus comprising a nozzle for picking up and mounting an electronic component, a voice coil motor including a shaft for moving the nozzle upwards and downwards, a gripping device for preventing the nozzle from free-falling by holding the shaft of the voice coil motor, an input/output control unit for controlling suction/evacuation of the nozzle and the gripping device, a voice coil motor control unit for positioning control of the voice coil motor and torque control of same by varying the amount of electric current supplied to the voice coil motor, a system control unit for instructing the positioning control and torque control to the voice coil motor control unit, and a position detector for detecting the position of the voice coil motor in upward and downward directions, the electronic component mounting method including a step of constant current control wherein a constant amount of electric current is supplied for a constant period of time to the voice coil motor from the voice coil motor control unit, the constant amount of electric current being preliminarily set in the voice coil motor control unit, and under circumstances where the positioning control of the voice coil motor by the voice coil motor control unit is impeded, the positioning control is switched to said constant current control, and the shaft of the voice coil motor is held by the gripping device during the constant current control.
With the above mounting method, even if the positioning control of a voice coil motor (VCM) for picking up and mounting electronic components by the VCM control unit is impeded due to over-loading, disconnection of a position detector, or an unexpected power failure, the positioning control is switched to constant current control, wherein a constant amount of electric current, which is preliminarily set in the VCM control unit, is supplied to the VCM from the VCM control unit for a constant period of time, during which the shaft of the VCM connected to the nozzle is grasped a gripping device. It is thus ensured that the nozzle will not free-fall and the electronic component mounting apparatus itself or a substrate onto which mounting operation is made are duly protected.
It is preferable if an amount of electric current supplied under a normal servo lock state is constantly recorded, and electric current is supplied in accordance with the most updated value to the voice coil motor during the constant current control, whereby the nozzle can be prevented from falling by grasping it with a force in accordance with variation in weights of the VCM just before the occurrence of the failure, electronic component, and nozzle, or changes of driving mechanisms with age.
While novel features of the invention are set forth in the preceding, the inve
Nakao Osamu
Shiomi Akira
Takeda Takeshi
Chang Rick Kiltae
Jordan and Hamburg LLP
Matsushita Electric - Industrial Co., Ltd.
Young Lee
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