The Challenge

To develop a system for measuring the various parameters of thin grinding wheels of different dimensions by providing an integrated, configurable and reliable test system in limited time and at very low cost. The automated test system measures the parameters like thickness, face run out, diameter run out and weight of the wheel.

The Solution

Using National Instruments LabVIEW™ 8.0 development environment, NI DAQmx, NI motion and other third party hardware provided a very flexible, reliable and powerful test system. The wheels of different dimensions were measured by adjusting the sensors to an exact measurement position using NI motion

Introduction

Our client, a leading manufacturer in grinding wheels needed an automated procedure of testing the wheels within a very short period of time to improve the quality of the wheels. The important parameters of the wheel needed to be measured were:

• Thickness of the wheel at three different positions
• Thickness variation throughout the wheel
• Face run out of the wheel
• Diameter run out of the wheel
• Weight of the wheel
• And some other derived parameters from the above measured parameters.

Three distance measurement sensors were used to measure the thickness, thickness variation, face run out and diameter run out of the wheel. The sensors were mounted on an “E” shaped mounting bracket surrounding the wheel and measuring thickness, face run out and diameter run out. The challenge was to adjust the position of the sensors to an exact measurement position of the wheels which were of different dimensions. Wheels were varying from three millimeter to eight millimeter of thickness. The middle sensor needed to measure the distance exactly from the center of the edge of the wheel.

We decided to build the system with National Instruments PCI 7334 2-axis motion controller card and PCI 6010 Data Acquisition card to acquire the data from three sensors and the load cell. The motion card was connected to two high torque stepper motors through an UMI 7764 interface. NI motion made it easy to adjust the sensor to an exact measurement position during the run time inspection. LabVIEW was the language of choice for programming the system due to its excellent graphical capabilities and tight integration with motion input outputs. The motion card’s Digital Inputs and Outputs (DIO) were used for the mechanical buttons and LED indicators.

System Design

The overall block diagram of the system is as shown in the figure below.

The wheels for testing were placed on a Wheel mounting shaft which is attached to an induction motor. This configuration is placed on the load cell. The stepper motors were connected to two Ball Screw Based Linear Slides. These slides are mounted one upon the other forming an XZ plane (horizontal and vertical). Vertical slide was mounted on the horizontal slide and the “E” shaped sensor mounting bracket was mounted on the vertical slide. The bore (inner) diameter of the wheels were of only two different dimensions hence the central wheel mounting shaft required only two steps, catering to all the various types of wheels being inspected.

The PCI 7332 motion card was used for the motion of the slides. During the time of inspection the vertical slide moves first then the horizontal slide. The distance measurement sensors proceeds to the measurement position as shown in figure 1. Complex interlocks were provided in the software so that the sensor does not hit the wheel and get damaged if a wrong wheel is placed. Once the measurement position is reached, the induction motor rotates the wheel on the shaft for one revolution. At this time all the sensors reading would be acquired through PCI 6010 DAQ card.

Software features

The two important features in the software were calibration of slides and the Inspection. During the calibration, operator would move the slide manually to the measurement and parking position and saves the position count of the vertical and horizontal slides to a file. This manual movement was provided with three mechanical buttons.

• Selector switch
• Left/Up
• Right/down

Selector switch would select which slide should be used for the movement (horizontal or vertical). Left/Up button would move the horizontal slide to left and vertical slide to upside. Similarly the Right/Down button is used to move right incase of horizontal slide and down incase of vertical slide. The saved position counts were used during the time of inspection of the wheel. The different types of wheels were named with an Item code and the corresponding calibrated counts of the slides were saved with this item code to the file.

The inspection flow is as give below

• User selects the Item code and opens the Inspection screen
• Slides move to their home position , which is the reference position for slides
• User initiates the start of inspection and slides move to their pre-calibrated parking position.
• User presses the Start (mechanical) button on the test bench. Slides move to the pre-calibrated measurement position. At the same, time interlocks are checked.
• Induction motor rotates the wheel for one revolution. Sensors acquire the data corresponding to the distance from the sensor to the wheel.
• Slides comeback to the parking position.
• System ready for the next wheel’s inspection.
• Next wheel can be placed on the shaft and the inspection can begin again by pressing the Start button on the bench and the sequence mentioned above is repeated

The distance between the top and the bottom sensors can be calibrated with a standard wheel of known thickness. With this known distance, the differential distance measured from the top and bottom sensors results in thickness of the wheel. Face run out is measured by the top sensor and diameter run out is measured by the middle sensor. All the data acquired is stored into a database which is used for the generation of report.

Conclusion

We were able to design and develop a test system that enabled our client to efficiently test the grinding wheels and provided the flexibility to configure/calibrate various kinds of wheels. NI LabVIEW development environment and the modularity extended by the NI motion equipped us in providing a flexible and reliable solution within a short duration of six weeks. Also the analyzed test reports were now ready available within minutes of completing a test, saving the customer valuable time and money compared to previous time consuming manual testing methods. The above solution reduced inspection time to one minute per lot which was ten to fifteen minutes of test previously. Also, the solution provided a centralized database for all the inspection results for analysis and tracing the items inspected, thereby increasing the production efficiency to a large extent.