Previous research has shown that operator performance of industrial machines is superior with position control rather than rate control, except for large-workspace and dynamically slow manipulators, which includes most hydraulic machinery. This paper describes an investigation to determine why position control leads to better performance than rate control except for with dynamically slow manipulators, in an effort to increase operator performance of mobile hydraulic equipment. It examines why dynamically slow systems are an exception to the general rule, and proposes a human-machine interface (HMI), called command feedback, that leads to position control having superior performance, even in these exceptional situations.
Thirty participants performed five tasks six times using one of five HMIs. A rate and a position controller were used to manipulate a dynamically fast system and a dynamically slow system that was designed to mimic the motion of hydraulic cylinders. A new HMI that provided real-time position feedback to the operator of his/her commanded position was applied to the position controller for the dynamically slow system. Task performance was measured and comparisons were made between position and rate control. The addition of the real-time position feedback to the dynamically slow system resulted in nearly identical performance with both controllers. From these results we conclude that position control is more intuitive for fast systems when human operators do not have the physical capability to control the velocity well with rate control, and that the intuitiveness of rate control for dynamically slow systems results from the lack of position feedback because of the machine’s speed of response. Command feedback can be used to elevate operator performance of hydraulic machinery.