April 2017 Archives

・ There are such products available that incorporate two sensors facing each other to ensure positioning with greater accuracy as a product design for increased processing data rate.

・ In this case, the sensors cost high and therefore, the designed assembly process may adopt temporary installation with fastening screws to prepare for possible reprocessing of any assembled products found insufficient in the accuracy of positioning in the assembly process (Fig.1).

・ In this production method, the components are fastened to each other with adhesive after proper accuracy is found to have been obtained by the temporary fastening with screws.

・ The positioning with use of fastening screws will inevitably cause factors for positioning errors as listed below (Fig.2).

(1) Deformation of parts caused by the rotational moment force generated by the tightening torque of fastening screws
(2) Variations in applied clamping force due to variations in friction resistance on the contact surface clamped by fastening screws
(3) Deformation caused by residual stress and its release of tightening torque

・ Those listed above in (1) through (3) will greatly depend on the number and arrangement of fastening screws.

・ One of the solutions to (1) and (3) includes tightening two fastening screws in opposite directions. Even in this case, the accuracy of positioning will be limited to a certain level due to differences in timing of tightening two screws and/or other factors (Fig.3).

Precautions

・ Even when tightening torque is controlled with a torque wrench, there are many other variable factors (e.g., parallelism between the surfaces to be fastened, friction resistance) involved and therefore variations in quality may not be totally eliminated, depending on the level of proficiency in the work.

-There is a thin stainless sheet with the characteristic of a flexible spring, having positioning holes provided by etching. (Figures1, 2).

-The etching process allows formation of precise reference holes for positioning on the hoop-shaped materials having a certain length for application of semiconductor processing.

-The reference positioning holes help ensure that the accuracy of pitch is consistently maintained at a high level. However, the shape of the reference positioning holes will inevitably suffer slight variations in the inside diameter and changes in the state of cross section of the inside diameter edge, which are caused by variations in the etching process (deterioration of etching solution, temperature, and other factors) (Figure 3).

-To avoid the effects of variations in the hole diameter, non-contact position alignment based on the image processing is most preferable, but this has a disadvantage of requiring high investment in equipment.

-Secure positioning based on the reference positioning holes may be attained using a proper fixture through selection of appropriate tip geometry of dowel pins and a design allowing the dowel pins to slide up and down (Figures4,5).

Precautions

-When dowel pins are used, the fixture reference plane and the bottom face of the etched sheet must be placed horizontally without any gap between them before positioning to other component parts.

・ In the case of liquid crystal display (LCD), eachelement 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.

From Vol. 284, we will introduce technical know-how and typical solutions that are specifically applicable to realizing automation and labor savings. The first topic refers to "Positioning" techniques.

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 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 [Figure51 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 minimize possible differences among individual operators in these tasks, standardization of the tasks is essential.