Development of an Energy Saving Hydraulic Stepper Drive

Abstract

Stepper drives can realize quite precise, incremental motions without position sensors. Sensorless hydraulic motion control is strongly demanded by industry and, therefore, is an established idea in hydraulics for a while. Some concepts have been proposed in the past and a few of them have also been realized and applied in specific cases. But it is expected that digital hydraulics — due to its intrinsic discrete nature — can create new, more advantageous hydraulic versions of stepper drives. In this paper, a new stepper drive is presented and investigated. It creates the steps by fixed fluid quanta generated by a so called digital flow unit. That unit is realized by a hydraulic cylinder-piston unit which displaces a defined fluid quantum by each limited forward stroke of that piston. The unit is controlled by a fast switching valve which connects the piston areas alternately with the pressure-, tank- and output-line. The return motion is generated by a return spring. Energy saving is accomplished by storing the supply pressure surplus intermediately in the kinetic energy of the piston and converting that energy to displace part of the quantum to the consumer line without hydraulic energy from the supply line. Different detail concepts of this stepper drive are theoretically assessed. The transient behavior, the performance characteristics and the energy efficiency of a preferred concept are investigated by mathematical modeling and simulation. Furthermore, the main system parameters are identified and corresponding basic dimensioning rules are presented. In a second step, the influence of finite switching times of the valves, the hydraulic impedances of the various flow channels and of the dead volumes and the dynamical properties of the hydraulic cylinder attached to the device, are discussed.

Simulation Research of Hydraulic Stepper Drive Technology Based on High Speed On/Off Valves and Miniature Plunger Cylinders

“…According to Newton’s Second Law, the piston motion can be expressed as the following [ 20 , 30 ]: where , , , , , , and denote the piston position, the mass of the piston, the pressure in the chamber, the load pressure, the piston area, the spring rate, and the preload of the spring, respectively.…”

“…Gradl et al proposed a new energy-saving hydraulic stepper drive with a hydraulic plunger cylinder and 3/2-way valve. With the hydraulic steeper drive, the flow rate can be controlled rather directly by adjusting the switching frequency [ 20 ]. The high-speed valves are cheap and robust, and they have a rapid response.…”

Investigation on the characteristics of a high-frequency two-dimensional rotary valve generating fluid pulse width modulation wave

“…The control oil is dispersed into the full stroke discharge oil volume of the plunger cylinder through two two-position three-way directional valves, in order to achieve the control of the discharge and reset actions of the plunger [8]. Gradl et al also proposed a similar solution and focused on studying its energy-saving characteristics [9]. Perry Li et al…”

A Comparative Study of Two Common Pump-Controlled Hydraulic Circuits for Single-Rod Actuators

“…One significant solution to improve the efficiency of hydraulic circuits is to design a system with no metering valves [3]. These systems are controlled through the pump and are recognized as pump-controlled or throttle-less hydraulic circuits [4]. In these circuits, pumps are directly connected to actuators, to provide the exact amount of pressurized flow required to achieve the specified motion, which leads to significant power savings [5].…”