WO1993023919A9 - Numerically controlled electric driving system with energy recovery function - Google Patents

Abstract

According to the invention, a numerically controlled electric motor driving system is provided including a control mechanism for energy recovery. The system includes a motor with an outer rare-earth metal made magnetic pole rotor (3) which is covered by a protecting ring (6). A stator coil (2) is provided connected to an adjustable inverted electric source (7) which passes through a high output digital switch set (9) and a filter set (10) to connect with a DC load (11). The DC load (11) controls the adjustable inverted electric source (7) and the digital switch source (9). The programmable control (8) is connected to the inverted electric source for changing the conventional AC or DC current into frequency and phase adjusted AC current output. By controlling the frequency and phase output of the inverted electric source, the rotation speed, acceleration and rotation direction of the rotor (3) can be managed. This provides the ability to recover energy and in the case of restored potential energy (raised elevator with load greater than counterbalance, lowered elevator with load less than counterbalance, raised crane with load greater than counterbalance etc.) whereby potential energy changes into mechanical energy and through the motor comes 3-phase AC current output.

Description

NUMERICALLY CONTROLLED ELECTRIC DRIVING SYSTEM WITH ENERGY RECOVERY FUNCTION

TECHNICAL FIELD OF THE INVENTION

This invention is about a numerically-controlled electric driving system which enables energy recovery through its reverse process.

BACKGROUND ART OF THE INVENTION

State of the art motor-driven machines divide into two main groups: induction and excitor. Since the operation theory and manufacturing process of induction motor-driven machines is very simple, there is a broad application in the manufacturing industry. The excitor has a more complicated structure, low accuracy of control and high maintenance expense. Both do not use numerically-controlled systems. Having a simple structure, higher efficiency that enables adjustment to various working conditions improvement (such as Chinese Patent application no. CN92100001.4) have been creased as a result. The unit described in Chinese Patent application no. CN92100001.4 can numerically control moving parameters such as speed, acceleration, direction,

torque and path for the pulled object. However, during the working process,

at the time the lifting facilities obtain energy to work (that is lifting cargo) from the supply current, a large portion of input energy is stored in machine parts in the form of potential energy. This process is called energy storage process.

And during the reverse process (that is landing cargo), the stored energy is not used properly. In traditional installations, a braking system is equipped to change potential energy to heat by the method of mechanical friction. The heat is dissipated through the air. This conventional method wastes lots of energy, and also the braking system easily breaks down.

SUMMARY AND OBJECTS OF THE INVENTION

It is an object of the invention to provide a numerically controlled electric motor driving system including energy recovery functions which system uses conventional components.

According to the invention, numerically controlled electric motor driving system is provided including a control mechanism for energy recovery. The system includes a motor with an outer rare-earth metal made magnetic pole rotor which is covered by a protecting ring. A stator coil is provided connected to an adjustable inverted electric source which passes through a high output digital switch set and a filter set to connect with a DC load. The DC load controls the adjustable inverted electric source and the digital switch source. The programmable control is connected to the inverted electric source for changing the conventional AC or DC current into frequency and phase adjusted

AC current output. By controlling the frequency and phase output of the inverted electric source, the rotation speed acceleration rotation direction of the

rotor can be managed. This provides the ability to recovery energy and in the case of restored potential energy (raised elevator with load greater than counter balance, lowered elevator with load less than counter balance, raised crane with load greater than counter balance etc.) whereby potential energy changes into mechanical energy and through the motor comes 3-phase AC current output. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a schematic cross-sectional view of a motor connected to other components forming the electric driving system of the invention; and Figure 2 is a cross-sectional view taken in an axial direction showing a motor structure used in the system according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings and in particular to Figure 1, the invention comprises an energy recovery numerically controlled electric driving system including a stator 1, stator coil 2, rotor 3 and rotor bearing 4. The outer part

of rotor 3 has rare-earth metal-made magnetic pole which is covered by

protecting ring 6. Outside the stator coil 2, there is an adjustable inverted electric source 7 which passes through a high-output digital switch set 9 and wave filter set 10 to connect with DC load 11, with the function of controlling the adjustable inverted electric source 7 and digital switch set 9.

Fig. 2 shows the cutaway view of the motor structure.

The stator 1, stator coil 2, rotor 3 and rotor bearing 4 make up the exchange system from electric energy to mechanical energy. Its purpose is the same as synchronous motor: a rare-earth-metal-made magnetic pole 5 is outside the rotor in order to make the rotor magneto. The AC current passes through the stator coil 2 to create a rotating magnetic field which works with magneto field to rotate rotor 3 in order to create a torque output. The rotation speed of the rotor has the same rotation speed caused by AC current. This invention uses the adjustable inverted electric source 7 to feed stator coil 2 and change the conventional AC or DC current into frequency and phase adjusted AC current output. Besides the control of frequency and phase adjustment, it can control the current demand. Through controlling frequency and phase output of the adjustable inverted electric source 7, the rotation speed, acceleration and rotation direction of rotor 3 can be managed. The rotor 3 output current can be adjusted through controlling output current of the adjustable inverted electric motor. Furthermore, the programmable controller 8 integrates the current and torque output of the adjustable inverted electric source for

controlling processing path.

As a conclusion, through the method of numerical control, the programmable controller 8 provides the ability to control the output such as rotation speed, acceleration, rotation speed, direction, torque and path on a

real time basis. This invention can be used with a crane. During the lifting process, the crane uses data obtained by the programmable controller (based on the working conditions and output requirements during the operation) to control rotation, acceleration, direction, torque and path throug the instructions of the adjustable inverted electric source. When the crane lands the cargo during the reverse process, a portion of potential energy changes into mechanical energy that passes through motor to become three-phase DC current. In other words, during the reverse process, the mechanical energy (formed by stator, stator coil, rotor and rotor supports) and electric energy exchange unit are in the working state of classical synchronous motor and so the three-phase AC current output exists in its lines. Then the three-phase AC current enters the adjustable inverted electric source 7 in which the three-phase doubleway rectifier bridge changes AC current into DC current. That DC current passes through the high-output digital switch set 9 and wave filter set

10 to reach a DC current load 11 for doing work. The purpose of the high- output digital switch set 9 is closing the connection when doing work and opening it during the reverse process. After the three-phase AC current changes into the DC current, the DC current can be transformed back into AC

current inside the adjustable inverted electric source, then sent back to the power supply. AU these procedures are controlled and coordinated by the programmable controller 8. The programmable controller's 8 control strategy and requirements are stored in its memory chip. Another way is using other computing systems to order control requirements which are passing through the programmable controller 8 to control the adjustable inverted electric source 7 and digital switch set 9. Therefore, the N.C. operation of the N.C. electric pulling system with energy recovery function is achieved. The rare-earth-magneto-made magnetic pole 5 has several separate stable pieces or can be one round piece. The magnetic pole 5 is covered by a protecting ring that is made of strong paramagnetic materials for standing high¬ speed rotation. The rotor is made of ferromagnetic materials (such as steel sheets, glass alloy and etc.) to have good magnetic conductivity. During the normal reverse process of doing external work, the potential energy is changed by the motor and its control systems to AC or DC current to do work. Besides saving unnecessary consumption and wearing out machine parts, this function increases the efficiency of energy consumption so that decreasing maintenance duty.

This model's adjustable inverted electric source 7 can use the Fuji Gl series inverters or the device described in Chinese patent no. CN90202757 or CN90203323 (Chinese Patents CN90202757 and CN90203323 are hereby incorporated by reference). There is no special technical requirement for this invention. The programmable controller 8 can be the controller for conventional industrial process or industrial control computer. Also, it can be the central computer or other control systems. Through the standard industrial control process, the programmable controller 8 controls the sensors and controlling mechanisms for the purpose of collecting data and controlling by the method of divided-time and divided-place.

Claims

WHAT IS CLAIMED IS:

1. A numerically controlled electric driving system including control for energy recovery, comprising: an numerically controlled motor including a stator, a coil and a rotor; adjustable inverted electric source connected to said coil for changing

AC or DC current into frequency and phase adjusted AC current output: a DC load connected to said adjustable inverted electric source via an output digital switch set and wave filter set; and programmable controller means connected to said adjusted inverted electric source for controlling frequency and phase output of said adjustable inverted source to control rotation speed, acceleration and rotation direction of said rotor.