Adaptive Control Firmware

Adaptive Control is a cutting edge technology that significantly improves the dynamic load control performance of an apparatus, leading to increased testing precision.

The GDS Adaptive Control firmware algorithm automatically adjusts the control gain values based on the observed specimen stiffness, removing the need for the user to enter a specimen stiffness value prior to the test.  This has the additional advantage of ensuring specimen stiffness changes during a test are also dealt with correctly. An example of this is observed during liquefaction testing, in which the specimen stiffness reduces considerably as the soil liquefies. When testing using an apparatus running GDS Adaptive Control, the firmware automatically optimises the control gains' values based on variations in soil stiffness as a cyclic test stage progresses, enabling a consistent loading amplitude to be applied to the test specimen.

This marks a significant improvement over traditional PID closed-loop systems which, especially when testing multiple specimens of varying stiffness, require the user to re-tune the system before each dynamic cyclic test as well as risk under-performance when specimen stiffness changes during loading. 

The loading system within a dynamic apparatus (whether open or closed-loop feedback) is controlled by the device's firmware. The firmware communicates with the loading system, and is typically programmed by the apparatus manufacturer. GDS have updated their dynamic control firmware to include Adaptive Control for the Advanced Dynamic Triaxial Testing System (DYNTTS), Dynamic Hollow Cylinder Apparatus (DYNHCA) and  Electromechanical Dynamic Cyclic Simple Shear Device (EMDCSS) as standard.

Key featuresBenefits to the user
The requirement for specimen-specific tuning before each test is eliminated:
Adaptive control systems automatically adjust their gains' values based on specimen response. This can speed up the cycling testing of soils and eliminate user error when tuning the apparatus specifically for each specimen.
The loading control system has variable gains, which are automatically optimised based on current specimen stiffness:Apparatus performance is significantly improved as specimen stiffness changes during dynamic cyclic loading. This results in a consistent loading amplitude being applied to soil specimens, even when large strains are applied.
Specimen-specific tuning may still be accessed for Adaptive Control if required:Enables specimens with stiffness noticeably different from those the apparatuses were tuned for to be cyclically tested using Adaptive Control.
DYNTTS & HCA can be switched easily between PID only and Adaptive Control options:The user has the flexibility to control using both Adaptive Control or traditional PID if required.

Graphs Comparing Adaptive Control Vs PID Performance

Below graphs show results from 2 deviator stress controlled tests of +/- 25kPa on identically prepared sand specimens.  One set of results uses PID only, the other set using GDS Adaptive Control.

PID Only Performance Graph

Adaptive Control Performance Graph

Note the reduction in deviator stress (i.e., the applied axial load) in blue occurring as the loading progresses past cycle number 20. Here the PID gains are fixed, so as the specimen softens the loading actuator does not move far enough to mobilise the targeted deviator stress amplitude of 25 kPa, and so full load during failure is not maintained. The axial strain applied to the specimen can be seen in orange, and does not exceed a double amplitude value of approximately 6 %.

Here the loading system correctly maintains the targeted deviator stress in blue as the test progresses up to cycle number 20. Here the PID gains are varied by the adaptive control firmware code, which works to reach the loading amplitude as the specimen softens. Note, in this test the double amplitude axial strain exceeds 20 % as the specimen fails, with the load target still being maintained, which is exactly how the test should have proceeded.

Products Available with Adaptive Control

To read an extended information document on Adaptive Control and to see the testing conducted but GDS download the PDF document here.

Adaptive Control Information and Test Data.