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Digital Shaker Vibration Controller - A Historical View(二)

Oct 19, 2017

First Generation VCS Inventors

One of the earliest digital VCS’s was developed by a Hewlett Packard engineers in the mid-1970s. HP researched many different close-loop control algorithms, using one of the earliest FFT-based signal analyzer systems, the HP5451. The HP5451 analyzer was based on an HP2100 mini-computer, which had very limited memory and computational resources. The HP engineers used various clever methods in trying to tackle the physical world that in general requires a few kilohertz of real-time bandwidth to control effectively. Two engineers, Ron Potter and Peter Moseley made many of the earliest contributions to the early generation controllers. 

After HP successfully tested the control algorithms with the HP5451, a dedicated VCS (the HP5427) was commercially produced in the late 1970’s.  It utilized the same computer architecture as the HP5451, but was packaged in a single bay of hardware, and dedicated to vibration control alone.  

Time Data Corporation, which later became a division of General Radio (GenRad), was also an early developer of a VCS product.  In the early 70s, two engineers at Time Data, Edwin Sloane and Charles Heizman, were granted a patent for random vibration control.  The GenRad GR25xx standalone control system was probably the most successful controller sold during the late 1980’s.  A GenRad VCS is shown below. 

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The vibration control group at the Structural Test Products (STP) Division of GenRad was later sold to the Spectral Dynamics corporation. Dr. Marcos Underwood, chief engineer for the GenRad controller, focused more on “error” control instead of the proportional control which was used by HP. Another Spectral Dynamics engineer, Tony Keller, also made many contributions to controller development in the early days. GenRad used Digital Equipment PDP-series mini-computers are the hardware platforms in their series of VCS’s. Beginning in the early 1980s, LMS (Leuven Measurement Systems, a Belgian company) worked together with HP to provide the vibration control software for HP’s new Paragon FFT analyzer hardware. LMS’s relationship with HP was similar to Microsoft’s relationship with IBM and the PC. Like Microsoft, LMS profited by selling only software that ran on the HP hardware. Other players of earlier generation VCS were Ling Electronics, MB Dynamics, and Schlumberger. The first generation VCS’s sold in the range of $80k to $200k, but they were very sophisticated and difficult to operate. However, most of the control algorithms in use today were developed during the 1970’s and early 1980’s. Also, the MIL810 testing standard, which sets the most comprehensive procedure of environmental testing including vibration test, was also established in this period.

Second Generation PC-Based VCS

In the early 1990’s, the IBM-PC began to gain popularity in industrial applications. Many companies started to use the PC as the platform for data acquisition and dynamic signal analysis. Sri Welaratna and Dave Snyder, two former HP engineers, founded a company called Data Physics and developed one of the first PC-based VCS’s. The Lansmont Corporation initiated a developmental program in collaboration with Data Physics which resulted in the production of the Lansmont TTVI controller and the DP540. This early DOS based controller had an impressive and flexible graphic user interface for that time period. The DP540 used multiple ISA plug-in DSP cards to the PC. Each card had several DSPs and A/D or D/A converters. Dr. James Zhuge was a key member of the Data Physics development team at that time. The product was very successful in the marketplace. 

In the same time frame as the DP540 (and later the Windows-based DP550) several other vendors released their own PC-based VCS; Puma from Spectral Dynamics, DVC from UniDyn, and VWin from Unholtz-Dickie.  

The second generation of VCS’s took advantage of the low price and graphics of the PC together with the signal processing power of dedicated DSPs. The usability and the performance of these products were greatly enhanced compared to their predecessors.  

The continuous drop in price throughout the 1990’s made VCS more affordable for commercial applications such as electronics and packaging testing. In addition, the market size for VCS increased moderately year by year. 

A shortcoming of second generation VCS’s was that they were heavily dependent on the performance of the PC. This was because the control loop relied on both the PC CPU and the PC plug-in cards that were installed in the PC. Many of the controllers mentioned above used the ISA bus which restricted the loop-time of the controller due to interrupts and the bus traffic bandwidth of the PC.  Even when a PCI bus was used, the PC CPU still played a significant role in the control process. In addition, the analog performance of the plug-in cards was limited due to interference from the PC’s physical and electrical environment. 

LMS and another company, m+p Corporation, continued to build software only VCS solutions using the HP Paragon or newer VXI hardware, and the UNIX operating system. They targeted mainly high-end customers where simultaneous data acquisition was also required during the test. 

Third Generation VCS - PC-Tethered

In 1996 Dactron Inc., founded by Joseph Driscoll (the Lansmont CEO) and Dr. James Zhuge, decided to pursue the next generation VCS. They recognized technical shortcomings in the existing technology and identified opportunities for improvement. The Dactron LASER series was developed as a next generation series of VCS products. The PC was still used, but it was viewed as a peripheral of the VCS instead of the center of it.  

In this new controller design, the control loop did not utilize the PC. With this strategy a much faster loop-time could be achieved. Many new algorithms were realized in the controller by taking advantage of floating point DSP chips. Justin Tang, the hardware manager at Dactron, designed the controller hardware, and George Ma, senior software engineer, designed the Windows software.  

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The LASER was the first VCS product that used multiple floating point DSP processors, 24-bit delta/sigma A/D converters and the PCI and USB technology. The original software was based on the native Microsoft MFC. This new signal processing technology and architecture allowed the system to perform many more functions while still maintaining its ease-of-use. In 2001 Dactron was acquired by LDS (Ling Data Systems), the world’s largest ED shaker manufacturer at that time. LDS has subsequently been merged with B&K (Bruel & Kjaer), a leading noise and vibration equipment vendor.  

After Dactron released the LASER and the Comet, other companies including VRC (Vibration Research Corporation) and DP introduced new generations of VCS’s using this same architecture with the control loop independent of the PC.  

Fourth Generation VCS - Networked

In 2010 Crystal Instruments, founded by Dr. James Zhuge, announced the release of Spider-81, the next generation of vibration control systems. The Spider-81 takes full advantage of the most modern signal processing algorithms and hardware plus the latest in software technology.  

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Spider-81 is the first network-based vibration control system that integrates the IEEE 1588 time synchronization technology into its design. The base module can be configured with 4 or 8 response channels, but the channel count can be expanded up to 1024 channels. This VCS design features very high reliability, high measurement accuracy, high control loop performance and ease-of use. Spider-81 is equipped with multiple drive output channels, bright LCD, digital I/O interface, internal backup battery and a RUN/Stop button. Spider-81 uses an Ethernet connection. 

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