Know-how on automation: Positioning technology

General description

One of the positioning techniques consists of magnifying the workpiece under a microscope for positioning and aligning the reference lines on the workpiece with the reference lines in an optical instrument (microscope in this case) (cursor lines in the eyepiece of the microscope). This is typically applicable to positioning of a magnetic sensor gap. In this method, the state of positioning becomes hard to see when the cursor lines in the microscope and the reference lines on the workpiece are aligned with each other. However, improvement in the design of cursor lines makes the state of positioning easier to identify even at higher magnifications.

Explanation

When the cursor lines in the microscope ([Figure1]) and the reference lines on the workpieces to be set in position are aligned with each other, the reference lines on the workpiece become covered with the cursor lines and thus become invisible, resulting in that it becomes hard to see the state of positioning ([Figure2]).

Then, typically, at a position with a small clearance left between the cursor lines in the microscope and the reference lines on the workpiece which are kept parallel to each other, the positioning is checked for proper state ([Figure3]).

In practice, however, this method makes it more difficult to identify the state of positioning in case where precise angular adjustment is needed (e.g., positioning of magnetic sensor) ([Figure4]).

As a solution to the case shown in [Figure4], improvement in design of cursor lines is recommended ([Figure5]).

The design of cursor lines shown in [Figure5] features ease of identification of both linear and angular positioning. Thus, it helps reduce the burden on the eyes in manual positioning under a high-power microscope or through a screen display.

Precautions

In the positioning based on the cursor lines, alignment between the cursor lines and the X- and Y-axes in the drive mechanism is critical, and setting of the origin of scale using gages and other tasks also become necessary. In order to minimise possible differences among individual operators in these tasks, standardisation of the tasks is essential.

In the case of liquid crystal display (LCD), each element is as small in size as several tens of µm. However, due to the large overall size, a huge number of elements of several tens of µm in size are arranged. In the case of the LCD shown in Fig.1, fine patterns at a pitch of several tens of µm are fabricated on the entire surface.

In the production technology for such fabrication, positioning with accuracy on the order of µm is essential for the X-Y table to arrange several hundred thousand to several millions of elements in a horizontal pattern.

A typical X-Y table is configured with robots moving in a straight line along the two (2) axes, X and Y.

In practice, however, the pulse generators adopted on the X- and Y-axes vary from the performance stated in the products-specifications. The differences in the timing of pulse generation appear in the form of accumulated errors in the repeatability of positioning accuracy on the order of µm (Fig.2, 3).

Even if individual errors are on the order of nm(nanometer), the extent of differences, when viewed with the human eye, looks like uneven irregularities, and thus the fabricated products may be defined unacceptable.

As a solution, such circuit design has been adopted that relies on one-pulse generator for controlling the pulse timing for all robots moving in a straight line for position alignment (Fig.4).

Precautions

In order to make the adopted solution effective, it is essential to control the accuracy of straight movement of the straight-line moving robots and the precision of the position alignment scales to the level equivalent to the required positioning accuracy.

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