A system for sending vernier digital gauge values into quality control reports and automatically calculating Cpk for automotive parts manufacturers in Thailand.

How the brief came about

The challenge in this case was to get values measured by digital vernier calipers directly into the quality report and have the system calculate the statistical values. Previously, QC staff measured workpieces with digital vernier calipers, wrote the values on a paper form, then calculated Cpk and other values themselves before issuing the report.

When figures have to be written down and calculated by hand, the same set of figures passes through people's hands several times, and each pass is a chance to misread or miscalculate. The customer, an automotive parts manufacturer in Thailand, therefore wanted reports that receive values from measuring tools and do the calculations themselves.

Requirements and constraints

The system had to work with Mitutoyo digital vernier calipers and the factory's server without connecting to the internet. The main requirements and constraints are as follows.

• Installed on the factory's Siemens industrial server (IPC), running Windows 10, and operating on the internal LAN only.
• Receive values from Mitutoyo digital vernier calipers both by cable through InGauge USB and wirelessly through U-WAVE.
• The report header must automatically pull in the part number, the date and the preset upper and lower specification limits (USL/LSL).
• Charts can be viewed by day shift, night shift or the whole day, and by part number.
• Calculate Cpk for each measuring point against the 1.33 criterion, and calculate control limits (UCL/LCL) from the whole month's data for use in the following month.
• Points out of specification (NG) must allow problem details to be recorded, and administrators must be able to specify users and report download permissions.
• Sending email from the system must wait until the factory's IT department enables the internal email server (SMTP).

How do vernier caliper values get into the report?

Vernier caliper values reach the report through a signal transceiver connected to the caliper, then go straight into the fields of the report page in the web app. QC staff still measure workpieces following the same procedure, but do not have to type or write down the values themselves. The vernier caliper can send values in 2 ways: through the wired InGauge USB signal converter, or through Mitutoyo's U-WAVE wireless transmitter.

The job requirement was a web app on the factory's server working offline on the internal LAN. Machines on the same LAN can therefore open the report page in a web browser. The system's workflow is as follows.

1. 1

   Measure the workpiece and send the value to the system

   QC staff measure the workpiece with a Mitutoyo digital vernier caliper, then send the value to the system through the InGauge USB signal converter or by pressing the button on the U-WAVE wireless transmitter attached to the caliper.

2. 2

   Select a machine from the overview layout page

   The overview layout page (Quality Layout) shows the production line layout and can be filtered to show only the lines you need. Users click a machine that has a report page to open that machine's report.

3. 3

   Values fill the report table automatically

   Measured values are arranged in the table in measuring-point order. The system immediately totals the results and finds the average of each set, and puts the part number, date and USL/LSL values in the report header.

4. 4

   Draw control charts and calculate Cpk

   The system draws X̄-R control charts (average and range) by shift and part number, calculates Cpk for each measuring point, then shows the status against the 1.33 criterion.

5. 5

   Record problems and manage permissions

   Points out of specification (NG) can have problem details recorded. Administrators use the Line Management page to manage users and approve report download permissions.

Deliverables

We delivered the QC report web app with 10 sets of InGauge USB, 10 tablets and 1 wireless router to an automotive parts manufacturer in Thailand in January 2021. The delivered items are as follows.

• Quality reporting web app, installed on 1 Siemens IPC server at the factory
• Overview layout page (Quality Layout) showing 33 production lines, and report pages for machines connected to vernier calipers, starting with machines in one production area of the factory
• Report pages with a table of measured values, X̄-R control charts, Cpk status, monthly control limits and problem recording for NG points
• Line Management page for managing users and report download permissions
• Equipment: 10 sets of InGauge USB, 10 tablets and 1 wireless router
• User manual and acceptance documents (Exit Criteria)

What was adjusted and added to the system after delivery?

After delivery, we adjusted the system following the customer's change requests (Change Requirement) several times in 2021. The main topics were shift times, separating genuinely defective parts from the chart, and managing users and report download permissions. We also moved some of the code from PHP without a framework to Laravel. The sequence of work is as follows.

1. 2020: Project started; web app and report pages developed
2. January 2021: Delivered the system, equipment, user manual and acceptance documents
3. 2021: Adjusted shift times, added a tick box to keep genuinely defective parts out of chart plotting, added management of users and secondary administrators (Sub Admin), and added report download permission requests
4. 2021: Project closed as completed work

Results confirmed from the delivery and project closure

The confirmed results are that we delivered the system with acceptance documents in January 2021 and closed the project as completed work in 2021. After delivery, QC staff can send vernier caliper values directly into the report and the system calculates Cpk, with no need to write values on paper.

This case has no measured business figures, so we report only the results backed by documents.

What we learned

The key principles from this work are to capture values at the source, separate specification limits from control limits, and agree early on any work that relies on the factory's IT systems. The details of each are as follows.

• Capture values at the source, then have every calculation use the same set of values. When the measuring tool sends values directly into the report, the table, chart and Cpk come from the same set of figures, with no need to copy them across several times.
• Separate specification limits from control limits. USL/LSL are specifications set per part number, whereas UCL/LCL are calculated from actual data of the previous month. The system must show these two values separately, and it must be clearly agreed which data goes into the chart, such as shift time boundaries and genuinely defective parts that should not be plotted.
• Functions that rely on the factory's IT systems must be agreed with the IT department from the start. In this work, sending email from the system had to wait for the IT department to enable internal SMTP.

How this approach can apply to your factory

If your factory already uses digital measuring tools but still writes values on paper, you can use the same approach as this case: send values from the measuring tools directly into the report, and let the system calculate the control charts and Cpk. What needs adjusting is the report form, the measuring points and the way the measuring tools connect, depending on the models you use.

• Start with a frequently used form that has clear measuring points. Once the formulas and report page are settled, expand to other machines and lines.
• Define the system administrators and the user permission approval sequence from the start.