Design and characteristic research of a novel electromechanical-hydraulic hybrid actuator with two transmission mechanisms

Abstract

Servo-hydraulic actuators (SHAs) are widely used in mechanical equipment to drive heavy-duty mechanisms. However, their energy efficiency is low, and their motion characteristics are inevitably affected by uncertain nonlinearities. Electromechanical actuators (EMAs) possess superior energy efficiency and motion characteristics. However, they cannot easily drive heavy-duty mechanisms because of weak bearing capacity. This study proposes and designs a novel electromechanical-hydraulic hybrid actuator (EMHA) that integrates the advantages of EMA and SHA. EMHA mainly features two transmission mechanisms. The piston of the hydraulic transmission mechanism and the ball screw pair of the electromechanical transmission mechanism are mechanically fixed together through screw bolts, realizing the integration of two types of transmission mechanisms. The control scheme of the electromechanical transmission mechanism is used for motion control, and the hydraulic transmission mechanism is used for power assistance. Then, the mathematical model, structure, and parameter design of the new EMHA are studied. Finally, the EMHA prototype and test platform are manufactured. The test results prove that the EMHA has good working characteristics and high energy efficiency. Compared with the valve-controlled hydraulic cylinder system, EMHA exhibits a velocity tracking error and energy consumption reduced by 49.7% and 54%, respectively, under the same working conditions.

Graphical abstract

Keywords

electromechanical-hydraulic hybrid actuator (EMHA) / integration / transmission mechanisms / power assistance / energy efficiency / working characteristics

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Nomenclature

Abbreviations
EHA	Electro-hydrostatic actuator
EMA	Electromechanical actuator
EMHA	Electromechanical-hydraulic hybrid actuator
SHA	Servo-hydraulic actuator
Variables
A1, A2	Effective action areas of the EMHA rodless and rod chamber pressure, respectively
B	Rotational viscous friction coefficient
c	System viscous damping coefficient
d	Outer diameter of the piston rod
dc	Outer diameter of the cylinder barrel
ds	Diameter of the lead screw
d1, d2	Diameters of the piston and piston rod, respectively
De	Servo motor width
Dz1	Wheelbase between the servo motor and the lead screw
Dz2	Wheelbase between the driving gear and the driven gear
Fe	Electromechanical transmission mechanism force
FE	Output force of EMA
FER	Radial force of the driving rod of EMA
Ff	Interference force including friction
Fh	Hydraulic transmission mechanism force
FH	Output force of SHA
FHR	Radial force of the driving rod of SHA
FL	Load force
Fsum	Total output force
id	Stator current of the d axis
iq	Stator current of the q axis
I	Current of the electrical unit
J1, J2	Moments of inertia of the servo motor rotor and reducer, respectively
Je	Moment of inertia driven by the electrical unit
JL	Equivalent moment of inertia of the load
Js	Moment of inertia of the lead screw
k	Reducer reduction ratio
l	Lead of the screw transmission pair
LE	Arm distance of the EMA output force
LH	Arm distance of the SHA output force
Ls	Equivalent inductance
m	Gear module
mh	Hydraulic oil mass
ml	Load mass
ms	Lead screw mass
n	Rotation speed of the servo motor
ns	Rotation speed of the lead screw
N	Number of the pole pairs
p1, p2	Pressures of the EMHA rodless and rod chamber, respectively
Ph	Driving power of the hydraulic cylinder
R	Stator resistance
T	Torque amplified through the reducer
Tadd	Additional torque of the distributed linear drive system
TL	Equivalent load torque of the servo motor
ud	Stator voltage of the d axis
uq	Stator voltage of the q axis
U	Voltage of electrical unit
v	Velocity of EMHA
vs	Linear speed of the lead screw rotation
x	Displacement of EMHA
z1, z2, z3	Numbers of the driving teeth, transition teeth, and driven teeth, respectively
α	Rotation angle of the servo motor
ψ	Flux linkage amplitude of the rotor permanent magnet
η1, η2	Efficiency of the mechanical and hydraulic transmission mechanism, respectively
θ	A certain angle
θE	Angle between the load force of the EMA driving rod and axis
θH	Angle between the load force of the SHA driving rod and axis

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant Nos. 51875385 and 51805349).

RIGHTS & PERMISSIONS

2023 Higher Education Press