PCBA Tech - About SMT chip processing sensor system

A variety of sensors are installed in the SMT placement machine, such as pressure sensors, negative pressure sensors and position sensors. These sensors constantly monitor the operation status of the placement machine during operation. The more sensor applications, the higher the level of intelligence of the machine.

1) Pressure sensor

The pressure system of the placement machine includes various air red working pressures and vacuum generators. These generators have certain requirements for air pressure. When the pressure is lower than the pressure specified by the equipment, the machine cannot operate normally. The pressure sensor always monitors the pressure changes. Once the machine is abnormal, it will promptly alarm and remind the operator to deal with it in time.

2) Negative pressure sensor

The suction nozzle on the placement head sucks the components by negative pressure, which is composed of a negative pressure generator and a vacuum sensor. When the negative pressure is not enough, the components will not be sucked. When the feeder has no components or the components are stuck on the feeder and cannot be sucked, the suction nozzle will not suck the components. The occurrence of these conditions will affect the normal operation of the machine. Work. The negative pressure sensor always monitors the change of negative pressure. When the component cannot be sucked or cannot be sucked, it can alarm in time to remind the operator to replace the feeder in time or check whether the suction nozzle and the negative pressure hose are blocked.

3) Position sensor

PCB transmission and positioning include PCB counting, placement head and workbench real-time monitoring, auxiliary mechanism movement, etc., all have strict requirements on positions, which are realized by various forms of position sensors. On the front track, there are generally two sensors. The sensor at the PCB entrance mainly detects whether the PCB is imported. Once the PCB is detected, the conveyor belt on the front track will run. If there is a PCB waiting or being attached to the middle track Then, the PCB at the entrance moves to the second sensor position of the front track and stops. After waiting for the PCB on the middle track to be exported, it is transferred to the middle track for placement. If there is a PCB waiting at the second sensor position of the front track, even if the sensor at the PCB entrance detects that there is a PCB, the conveyor belt on the front track will stop running and be in a waiting state. The sensor on the middle track mainly detects whether there is a PCB waiting to be mounted. If a PCB is detected, the placement program will quickly run, and the components will be mounted to various positions on the PCB according to the instructions. After the components on the PCB are assembled, they are quickly imported to the back-end track, and the conveyor belt on the back-end track will run to export the mounted PCB to the next process. If PCB blockage occurs at the exit of the rear track, even if the PCB on the middle track is mounted, the PCB will not be exported. During the placement process of the placement machine, the placement head moves at high speed along the% axis and the y axis. In order to prevent the placement head from hitting the arm of the machine, there are two limits in the X axis and y axis directions of the placement machine. Position sensor, once the placement head reaches the limit sensor, the machine will immediately stop running. It can be seen that the limit sensor mainly protects the placement head.

LED lighting patch processing 009

4) Image sensor

The real-time display of the working status of the placement machine mainly uses a CCD image sensor, which can collect various required image signals, including the position of the PCB, the size of the components, and through computer analysis and processing, so that the placement head can complete the adjustment and placement Work.

5) Laser sensor

Laser has now been widely used in placement machines, it can help determine the coplanarity of device pins. When the device under test runs to the monitoring position of the laser sensor, the beam emitted by the laser illuminates the IC pin and is reflected on the laser reader. If the reflected beam is the same as the emitted beam, the coplanarity of the device is qualified; when When they are not the same, the device leads to deformation, which makes the emitted light beam longer, and the laser sensor recognizes that the device leads are defective. In the same way, the laser sensor can also identify the height of the device, which can shorten the production preparation time.

6) Area sensor

When the placement machine is working, for the safe operation of the placement head, sensors are usually installed in the movement area of the placement head, and the operating space is monitored by the photoelectric principle to prevent damage from foreign objects.

7) SMD head pressure sensor

With the improvement of the speed and accuracy of the placement head, the intelligence requirements for the placement of the components on the PCB of the placement head are getting higher and higher. This is the commonly referred to as the "z-axis soft landing" function, which uses pressure sensors and servos. The load characteristics of the motor are realized. When the component is placed on the PCB, it will be vibrated at the moment, and its vibrating force can be transmitted to the control system in time, and then fed back to the placement head through the adjustment of the control system, so as to realize the z-axis soft landing function. When the placement head with this function is working, it feels smooth and light. If you observe further, the depth of the solder paste immersed when the components are placed on the PCB circuit board is roughly the same, which prevents tombstones during subsequent soldering. Welding defects such as, misalignment and flying pieces are also very beneficial.