DD287828A5 - DEVICE FOR DETECTING THE POSITION DEVIATION OF LADDER RAILS OF A PCB TO A REFERENCE POSITION - Google Patents

Abstract

The invention relates to a device for determining the positional deviation of printed conductors of a printed circuit board with respect to a desired position, which is connected to the Bestückckkopf a printed circuit board automatic machines. According to the invention, a light source, two convex lenses, a beam splitter cube and another convex lens are arranged on an optical axis. On the outlet side of the beam splitter cube, a semiconductor receiver is mounted, which communicates with evaluation electronics. A mark as part of the PCB layout reflects the parallel, vertically incident light from the light source over the beam splitter cube onto the semiconductor receiver. Its signals are converted by the evaluation electronics into output voltages which determine the position of the mark in relation to the device. The device requires a minimum of hardware and software. Fig. 1 {determination; Correction; Position deviation; Actual position; Target position; Conductor tracks; Printed circuit board; convex lenses; Strahlenteilerwuerfel; Light source; Halbleiterempfaenger; evaluation; PCB layout}

Description

For this 2 pages drawings

Field of application of the invention

The invention relates to a device for determining the positional deviation of printed conductors of a printed circuit board with respect to a desired position, which is connected to the placement of a Leiterplattenbestückautomaten. With this device, it is possible to determine position deviation without great gerstetechnischen effort to subsequently perform position corrections can.

Characteristic of the known state of the art There are devices for the assembly of printed circuit boards with attachable components known after the so-called

»Pick and Place'-Prlnzlp aiboiten.

The components are removed from a mounting head by means of a vacuum pipette from a component memory and on

the printed circuit board positioned remotely.

The circuit board has special positioning holes, over which the circuit board by means of pins in the exact position Placement machine is fixed. Since the conductor pattern with respect to a defined desired position and consequently also to the Positioning holes may have considerable deviations in location, the exact alignment of the circuit board or

of the placement head opposite the conductor pattern a major problem in the assembly. This position correction requires a measuring system for determining the position deviation.

Internationally known are placement machines with Lagekorrektursystemen, either fixed part of the machine or

are available as accessories.

Corporate typefaces are known from the following optical correction systems:

(1) Company brochure Dy η a pert M PS 2 500

"High-speed SMD assembly" | 2 | Company brochure ZEVATECH

Assembly system PPM 7 (3) Company logo Siemens

SMD-Besiückautomat M S-90

In Dynapert [1] a device is described which uses CCD cameras to determine the position of correction marks at certain points of the oil image. After their deviation from the programmed target position, the computer determines a mean x-axis correction and rotation and transmits the appropriate control command »to the machine. With this so-called fiducial correction system, the component positioning at offset in the conductor pattern is tracked to an average value determined individually for each printed circuit board. This facility can be extended to a so-called pattern recognition system. A CCD camera compares the position of the component terminals with the length of the contact pads on the PCB before each assembly. The computer corrects the x- / y-coordinates of the positioning element and the rotation of the placement head, so that the component is placed in the correct position on the soldering surfaces. The average measuring cycle time is given as four seconds.

At ZEVATECH | 2 | an automatic correction of the conductor image offset by means of CCD camera and image processing computer is described. A so-called TLC station (Touchless Centering) is described for equipping higher-pole components jn. A CCD camera detects the position and geometry of the components opto-electronically. After the measurement, the component is picked up from the placement and equipped in the correct position with the highest precision in consideration of the measurement result. The average measurement cycle time is four seconds.

Siemens (3) uses a video position correction system. With a mounted on the placement CCD camera suitable Justierstrukturen be recognized on the circuit board and corrects the placement positions of the components accordingly. The sampling time per reference mark is 150 to 300 milliseconds.

The basis of the correction devices just described is the use of CCD cameras. The disadvantage here is in particular the relatively high hardness of hardware and software, the comparatively slow operating speed and the relatively high investment costs.

In addition, a corresponding image processing computer is used in all correction devices, which is not required for some applications.

Object of the invention

The Ziei of the invention is to provide a means for determining the positional deviation of printed conductors of a printed circuit board against a desired position available, with little effort on hardware and software and sufficient reliability.

Explanation of the essence of the invention The invention is based on the object, a device for determining the positional deviation of printed conductors of a To provide printed circuit board with respect to a desired position by means of an analog optical measuring system and evaluation electronics,

with high sensitivity and processing speed in a small design with low mass.

According to the invention, this object is achieved in that a light source, two convex lenses, a beam splitter cube and

another convex lens are arranged on an optical axis. It is on the exit side of the beam splitter cube a

Semiconductor receiver applied, which is connected via a connecting line with the transmitter in combination. Conveniently, said components are housed in a housing which fixed to a placement

a printed circuit board placement machine is arranged.

It is also possible for the semiconductor receiver to comprise a quadrant photodiode, a full-area photodiode, a circular Circular photodiode, a differential photodiode or a strip photodiode is. Instead of a beam splitter cube, a semitransparent mirror can also be used. A mark as part of the printed circuit board layout reflects the parallel, vertically incident light from the light source Beam splitter cube on the position sensitive semiconductor receiver and is displayed there. To the semiconductor receiver

is connected to a processing electronics, from whose output signals the position of the device is determined against the brand.

By means of the device according to the invention, it has become possible to deviate in the position of conductor tracks of a printed circuit board

high sensitivity and high processing speed. In this case, a minimum of hardware and software is required, with sufficient 2'usicherheitigkeit the device of the invention.

Ausfuhrungtbelsplel The invention will be explained in more detail using an exemplary embodiment. In the accompanying drawing show Fig. 1: the structure of the device; Fig. 2: the position of the device in the desired position; Fig. 3: the position of the device in actual position. 1, a light source 3, a convex lens 4, a Kovexlinue 5 is in a housing 1 on an optical axis 2 a Beam splitter cube collar arranged a convex lens 7. On the exit side 6.1 of the beam splitter cube 6, the softer

From a printed circuit board 8 reflected and β deflected in the beam splitter Wave rays exit, a semiconductor receiver in the form olner position sensitive quadrant photodiode 9 is applied. An evaluation 10 is connected via a

Lead 11 connected to the quadrant photodiode 9. The transmitter 10 may also be in the housing. 1

be housed.

The housed in the housing 1 device is connected to a placement of a Leiterplattenbestückautomaten, not shown

firmly attached, so that the optical axis 2 is perpendicular to the circuit board 8 and one applied to the circuit board 8

Mark 12 is sharply displayed on the quadrant photodiode 9. That of the light source 3 and the convex lenses 4; 5; 7 generated homogeneous radiation field is reflected by the circuit board 8. The mark 12 is imaged by the convex lens 7 and the beam splitter cube 6 on the quadrant photodiode 9,

wherein the beam splitter wafer 6 decouples the reflected light from the incident light.

The transmitter 10 v / delt the four output currents of the quadrant photodiode 9 so dsS the output voltages Ux

and Uy take the value zero when the geometric center of gravity of the quadrant photodiode 9 with the optical

Center of gravity of the resulting on the quadrant photodiode 9 image of the mark 12, then, if the optical Achsn 2 goes through the optical focus of the brand 12. To determine the positional deviation of the printed circuit board 8, the placement head, not shown, with the described Device brought to the nominal position of the mark 12. In this position the output voltages Ux and Uy are measured

(Figure 2). If the output voltages Ux or Uy are not equal to zero, the placement head is moved in the two coordinates until the output voltages assume the value zero (FIG. 3), the travel direction in the respective one

Coordinate from the sign of the corresponding output voltage is derivable. This on the control of the Placement head drives determinable travels Wi id the position deviations in x- and y-direction of the actual position compared to Target position of the brand 12 and thus the circuit board. 8

Claims (3)

1. A device for determining the positional deviation of printed conductors of a printed circuit board with respect to a desired position by means of an analog optical measuring system and an evaluation, characterized in that a light source (3), convex lenses (4; 5), a beam splitter cube (6), and a further convex lens (7) are arranged on an optical axis (2), that on the outlet side (6.1) of the beam splitter cube (6) a semiconductor receiver is aufgeiacht, which communicates via a connecting line with the evaluation electronics (10). 2. Device according to claim 1, characterized in that the components are housed in a housing (1) which is fixedly arranged on a placement of a Leiterplattenbestückautomaten. 3. Device according to claim 1 and 2, characterized in that the semiconductor receiver consists of a quadrant photodiode (9), a full-area photodiode, a differential photodiode, a strip photodiode or a circular circular photodiode.