Development of an intuitive user interface for a hydraulic backhoe

This paper describes the development of an intuitive user interface for controlling a hydraulic backhoe, a piece of excavating equipment with a digging bucket on the end of a two-part articulated arm typically mounted on the back of a tractor or front-end loader. Controlling a backhoe requires a highly trained operator to control several hydraulic actuators simultaneously with fine inverse kinematic mapping. With this work, we propose a novel joystick configuration with hybrid cylindrical coordinate and independent bucket control, in which each joystick can execute horizontal and vertical movements of the backhoe. For this, a robotic controller scheme with a joystick rate control has been developed. The proposed method allows an operator to control the hydraulic backhoe intuitively and operate complex motions smoothly with no constraints. The suggested joystick scheme has several advantages compared to Cartesian coordinated control methods as follows; 1) independent horizontal and vertical motion control 2) more natural and intuitive for excavator works 3) less complicated and expensive 4) closer to conventional joystick operation mode and 5) easy return to standard mode by software. A virtual simulator and an actual backhoe test bed were developed to demonstrate the effectiveness of the proposed interface scheme. Preliminary user studies were performed for flattening and digging tasks using the virtual backhoe simulator interfaced to real joysticks. The results showed that the proposed intuitive interface facilitated faster and more precise operation than the conventional actuator control scheme. The controller was designed hierarchically to achieve the suggested joystick configuration control of the hydraulic backhoe system with electric joysticks. This included high-level control for rate control of the joystick, mid-level control for end-effector disturbance compensation, and low-level control for robust control of the hydraulic cylinders. The prototype backhoe with hydraulic control system had maximum position errors of 3 cm for vertical, horizontal, and slope movements with intuitive coordinate operations, making it more functional for performing various excavating tasks in natural and effective ways.