There are cases where a hydraulic excavator does not perform the accurate digging operation due to the influence of the resistance force when the bucket tip contacts with the unknown object in the ground. To resolve this problem, we propose a method combining model predictive control and servo mechanism. Model predictive control with servo mechanism, which we call as MPCS, predicts the future motion and suppresses the influence of the unknown disturbance. Thus, MPCS can remove the influence of the resistance force owing to servo mechanism which increases the control input using the error integration. Moreover, it suppresses the deviation from the target shape owing to model predictive control which predicts the future motion and considers constraints when the resistance force has disappeared. In this paper, we consider constraints of the magnitude of the control input and the maximum discharge flow rate of the pump in MPCS. We show the effectiveness of MPCS through the experiment including collision with the unknown objects.
We introduce a new particle excitation control valve that is driven by a vibration of a different direction from the previous particle excitation control valve. Conventional small hydraulic servo valves have some disadvantages such as a complex structure and waste of hydraulic energy. As a way to solve these disadvantages, we study a hydraulic small control valve using a piezoelectric vibrator. We confirmed that the proposed control valve was operated with low viscosity fluid in our previous research. However, the control valve was not operated with high viscosity fluid, because a force required to open the valve is increased due to rising of the viscosity. In this paper, we fabricate a new prototype valve driven by the perpendicular vibration to the flow direction in order to achieve the operation of the valve with the common hydraulic oil, and evaluate the characteristics of the valve due to changing the valve seat shapes. As a result, we found that the taper angle of the valve seat has an optimum value. When the taper angle of the valve seat is 100°, the prototype valve was opened by the lower voltage than the other taper angles. In addition, when the silicone oil was used as the working fluid, with kinematic viscosity values of 30㎟/s, which is nearly equal to the kinematic viscosity of the common hydraulic oil, we have succeeded in opening the valve at 0.8MPa. Since the previous particle excitation valve cannot be opened in the high viscosity working fluid, these results indicate the possibility for operating the proposed valve with the common hydraulic oil.
In the previous report, a newly designed electro-magnetic proportional actuator composed of an armature and a stator with a cylindrical two-step pole to control oil hydraulic valve was suggested. This actuator generates a large thrust force. The principal of generating the force was explained in detail in the report, however, the characteristics of heat transfer and thrust force of the actuator, in the case of varying the outer size, have not been examined. In this study, when the size of the actuator is varied, the characteristics of heat transfer in the case of continuous energization and the thrust force are examined. As a result, the characteristic length of the actuator’s relationship with the electric power consumption, thrust force and working stroke became clear. A method in making diagrams on the relationship between the outer size and performances of the actuator is suggested. In conclusion, based on the request of performance values of the actuator, the outline of designs may be carried out easily using the above-mentioned relationships.
In this study, we proposed processing the inner surface of cylinder-like parts with a magnetic compound fluid (MCF). We determined the processing characteristics of material removal and the changes in surface roughness and shape accuracy. The processing tool was a round SUS bar with a permanent magnet inserted in it. Processing was performed by coaxial processing and eccentric processing. In the processing experiments, material removal and surface roughness were found to have peak values as the processing surface shear rate increased. An observation experiment was conducted to clarify the behavior of magnetic clusters during MCF processing. We clarified the shape and distribution of the clusters and the processing speeds at various rotation speeds of the processing tool. The magnetic clusters were found to expand with the existence region in material removal peak. Through the processing speed measurement experiment, it was clarified that the MCF exhibits elastic behavior during processing.