Emerson Process Management

DoctorKnow® Application Paper

Title:	Using PeakVue and an Automated Online System to Control Product Quality
Source/Author:	Bill Broussard
Product:	Online
Technology:	Online
Classification:	Advanced

Using
PeakVue
and an
Automated Online System
to
Control Product Quality

Bill Broussard

1.0 Introduction

Through the application of Predictive Maintenance (PDM) technologies, manufacturing processes have been effectively and efficiently improved. Vibration analysis has assisted engineers and technicians in detecting and diagnosing countless problems they have encountered with their machinery, including structural problems.

Automotive manufacturers have taken this to the next level. Any supplier of parts utilized in the manufacture of an automobile must meet the requirements of QS 9000. One of the many purposes for this certification is to insure that quality parts are manufactured. Insuring this quality has proven to be a challenge in many cases, such as the one presented in this paper.

A leading manufacturer of ventilation system actuators was tasked with improving the efficiency of their part certification process. This process required someone to sit and audibly listen to the actuators operate. If any noise was heard, the part was rejected. A scratch on a gear, a defective gear tooth, or other defects may cause this noise. As you can see, this is not a cost-effective method of qualifying the manufactured parts, nor is it efficient.

Seeking a solution to this problem, engineers at the plant were able to prove a correlation between the noise and vibration levels. Computational Systems, Inc. (CSI) was contacted and asked to provide a solution for this need. CSI installed a system that is able to measure the vibration level and "flag" the part as pass/fail in a matter of seconds. The purpose of this paper is to present this unique solution and perhaps provide insight into a problem that you may be encountering.

2.0 Background

Over the last decade, automobiles have become more and more complicated in their design. Actuators are used to control the dampers in your ventilation system. If there is a defect in the actuator, it is likely that this small noise can resonate throughout the ventilation system. This resonation causes a noise that is generally unacceptable by the owners of the automobile.

Looking at the design of the actuator, there are many places where a defect will generate an unacceptable noise. Providing the driving force for the actuator is a 12 VDC motor. On the motor shaft is a brass worm gear that interfaces with a helical gear that has 35 teeth. Gearmesh for this interface is 2000 RPM and the turning speed of the helical gear is 57.1 RPM. This interface is the main focus of the testing process. Since the actuator has a limited amount of travel in its application, only the worm gear and helical gear make a complete revolution during normal operations.

To maximize the production level of these actuators, the manufacturer is attempting to reduce the cycle time for each actuator to four seconds at each station in the line. The manufacturing process builds the actuators on a pallet piece-by-piece. Each pallet will hold two actuators. Attempting to keep within the four-second-cycle time per actuator, CSI had to be able to collect vibration data and process it within eight seconds. But wait, we must first subtract out the time it takes for pallet handling. This includes the movement of the pallet from a staging point into the vibration test cell, and then moving the pallet out of the test cell. Eight seconds is the maximum amount of time from one pallet being released from the staging point until the next pallet is released.

One other consideration must also be made. These actuators operate the ventilation dampers, and these dampers open and close. This means that the actuators operate in a clockwise and counter-clockwise direction. Therefore, testing must occur in both directions as well. This is due to the fact that a defect may be present on a gear tooth in one direction, but not in the other. Many of these actuators fail testing in one direction only.

3.0 Solution

Figure 1 3130 Online System with Relay Panel and Test Cell

CSI proposed the installation of a 3130 Online Monitoring system controlled by a set of relays (Figure 1). Once the pallet is in place in the vibration test cell, a power source is applied. When the motor is running, the Programmable Logic Circuit (PLC) tells the 3130 system when to begin collecting data. This communication process is controlled by a relay. Once the PLC sends a signal to the relay stating that the pallet is in place and power has been supplied, the relay changes state and sends a signal to the 3130 to begin data collection.

Figure 2 Relay Panel and PLC Circuits

Data collection is setup to capture data in both directions. To insure that there is enough time to capture all the required data, the analysis parameters are set so that a four-second data capture will occur. Actual settings are for a 400 Hz spectrum with 1600 lines of resolution. During the data collection, the PLC is programmed to stop the motor and reverse directions. By collecting four-seconds of data, we were able to insure that the actuator is tested in both directions with sufficient time to allow one complete revolution of the helical gear. Stopping the motor and reversing the direction does create a spike in the data, however, this spike is not of sufficient amplitude to cause any false failures. By performing a controlled reversal of direction, we are able to minimize the amplitude of the spike.

Capturing of the data is only the beginning of providing the full solution. Normal vibration data and analysis still does not reflect the defects in the actuator. All gears in the actuator are plastic, not metal. The only metal parts are the motor casing itself and the brass worm gear. CSI has patented a special processing method called PeakVue. PeakVue detects and processes stress waves in a fashion that no other technique can match. It has proven to be superior to demodulation and normal vibration techniques. PeakVue was originally designed to address the difficulties in accurately analyzing gear defects. This seemed like a logical choice for the actuator application. The only unknown was how well PeakVue would perform with all plastic gears. Throughout testing, PeakVue proved to be the perfect choice for this application.

Figure 3 Two general purpose accelerometers mounted in specially designed housings

Raw vibration signals are detected with two general-purpose accelerometers that have been mounted in a special housing (Figure 2). There are multiple purposes for the special housing. One is to provide protection for the sensors themselves. Another is to allow spring mounting of the sensors to insure they are not damaged when the actuator housing and sensor make contact. Pallets are raised into position for the vibration data collection. Raising the pallets minimizes the stress and strain that would be placed on the accelerometer cabling if the sensors were mounted on the moving part. A gimbal is included as a part of this housing insuring good contact with the surface of the actuator housing.

Outputs of the two accelerometers are then passed into two SPV 305 (Synchronous PeakVue) units. These units process the incoming data using the PeakVue process. The output of these units are then passed into a multiplexer board that will process two channels of data simultaneously. After all of this pre-processing, the final waveform is then processed and compared to the alarm level. For this application, we are only interested in the peak-to-peak value for the waveform. Spectral data does reveal good diagnostic data, but this application is simply a go/no go application.

Lastly, this process involves the flagging of the parts that have failed. If a part exceeds the preset alarm limit, an alarm is enunciated to an output relay. The state of the output relays is read by the PLC, and if an alarm is present on either channel, it will cause the associated part to be flagged as a "bad" actuator. Flagged parts will be removed further down the line as the pallet progresses.

4.0 Conclusion

Innovative thinking is often the solution to the challenging problems. By having the tools that were necessary, CSI was able to design and provide a complete and simple solution to the customers need. This system not only met the proposed concept, but far exceeded it. Certification testing for these actuators has now been made more efficient and effective.