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Spin-off Technologies

During the development of a new device, we occasionally run into a limitation in existing technology which must be addressed in order to continue making progress on the primary development path. The solution to these secondary problems can be a significant departure from current technology. Here are a couple of examples of the technology advances that we at Active Signal have made to overcome technical problems encountered in our development work.

High speed LVDT position feedback

Problem: An existing hydraulic valve assembly with an integrated Linear Variable Displacement Transducer (LVDT) must be incorporated into a new application that requires position updates at a rate that exceeds the LVDT manufacturer recommended drive frequency. Driving the LVDT at a higher frequency is not an option since the manufacturer will not guarantee the linearity of the device beyond the stated drive frequency specifications. Traditional LVDT position resolution circuitry and algorithms typically provide position updates once every ten cycles of the LVDT drive frequency.

Solution: We developed a predictive algorithm which allows us to get accurate LVDT position updates at up to ten times per cycle of the LVDT drive frequency. This algorithm was incorporated into a dSPACE system which was used to successfully close a control loop around the hydraulic system being developed. This new system was capable of operating at many times the typical response frequency of a traditional hydraulic control system.

High speed electronic piston / valve synchronization

Problem: Synchronize, with 1 degree of angular resolution, a high speed hydraulic pump piston with a six port high speed rotary valve. Active Signal developed a Terfenol-D driven hydraulic pump as part of a DARPA Compact Hybrid Actuator Program (CHAP) program. The pump piston needed to operate at a cycle rate of 3000Hz in order to achieve a high energy density and a practical flow rate. To do this, the pump incorporated a high speed six port rotary valve (U.S. patent number 6,751,954). The required valve drive speed is 30,000rpm and is powered by a brushless DC motor. This means that the pump piston cycles 6 times per revolution of the valve. By using a 9 bit absolute magnetic encoder on the valve drive shaft we get a valve position accuracy of 0.7 degrees every 3.9 microseconds, but this only allows 4.2 degrees of piston to valve position accuracy.

Solution: Working with Mink Hollow Systems Inc. (Ashton, MD) we were able to develop a “virtual camshaft” that synchronized the piston and the valve using a LabVIEW™ hardware and software system. This allowed us to control the synchronization between valve porting and pump piston position with an accuracy of 1.05 degrees at full speed. This solution was described in an article written by Mink Hollow Systems which was published by National Instruments, and featured in another article by Design News.


If you are interested in further information concerning any of these technologies or, if you have encountered a technological hurdle or barrier in your project that requires a “unique” solution then perhaps we can be of assistance.