Electrical generator or motor structure – Dynamoelectric – Reciprocating
Reexamination Certificate
2000-09-13
2004-06-01
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Reciprocating
C310S017000, C388S937000, C029S039000, C029S02700R
Reexamination Certificate
active
06744155
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a motor, in particular a linear motor for a machine tool or a pump, wherein the movement of the motor can be controlled without requiring correction of the movement of a reaction section.
Workpieces or tools are moved in many machines in industrial production processes, with the movement taking place along fixed, predetermined axis tracks. The rate at which the machine operates depends essentially on the speed of the adjustment and transport movements. High axis speeds are thus desirable in order to achieve high machine productivities.
In most cases, the adjustment movements, which need to have a certain precision, are carried out by controlled electrical servo drives. In order to take account of the considerably more stringent requirements for accuracy and speed, direct drives have been increasingly used for many years for high-precision adjustment and transport movements. In direct drives, the feed or rotation force required for the movement is produced by a motor or a power converter and is introduced into the useful load without passing through any gearbox or mechanical transmissions. Appropriate servo motors and linear motors are available. The high accelerations and major jolts (rate of change of acceleration) which occur with rapid axis movements lead to vibration in the machine structures, and thus to negative influences on the processing results.
Like all motors, direct drives also have two mutually paired active surfaces, between which the drive force is built up as a consequence of the feed to the motor. The motor power or the motor torque is essentially proportional to the magnitude of the feed, or is linearized by suitable electronic distortion compensation. The feed side of the motor is referred to as the “active side”. As an example, a linear motor will be considered here, whose active section is also called the “primary section”. Both arrangements in which the active section is connected to the useful load and arrangements in which the passive section drives the useful load are in widespread use. That motor section which faces the useful load is referred to as the “output-drive side” of the motor. The side of the motor facing away from the useful load is referred to as the reaction side in the following text.
In order to transport the useful load as precisely as possible to the predetermined set positions, the actual position is detected by means of a position measurement system, and is supplied to a control unit. The position errors are evaluated here, and a calculated motor power is applied in order to accelerate the useful load so that the undesirable position error is reduced again. This process is referred to as control.
DE 23 54 947 discloses a linear motor which is based on vibration-damping bell elements and which is used in areas in which there is no requirement for high movement precision, for example for hoists, crane carriages, etc. This bearing ensures that the motor starts “smoothly”.
However, in machine construction, it is assumed that drive units which are intended to carry out precise and rapid movements need to make contact with their reference masses in as fixed (rigid) a manner as possible. It is therefore always desirable to couple the motor output-drive side to the useful load in as fixed a manner as possible and to couple the motor reaction side to the base in as hard a manner as possible. In order to achieve this, DE 297 18 566, for example, provides for the motor reaction side to be coupled to the base via a material providing a high level of vibration damping (considerably greater than that of steel). It is likewise of critical importance to connect the position sensors, which are part of the control system described above, to the reference bodies in as fixed a manner as possible, and with as little vibration as possible.
During dynamic movement processes, the predetermined route curves produce high momentum changes, which must be transmitted through the direct drive to the useful load. Since the momentum is maintained, the motor reaction side has to absorb the opposing momentum. This momentum is introduced directly into the base, owing to the hard connection. This leads to severe vibration of the machine reference body, for example the machine bed, which may have disadvantageous effects on the accuracies and surface quality of the processing.
The article “A Fast-Tool-Servo System based on electrodynamic and piezoelectric Actuators” (Annals of the German Academic Society for Production Engineering 2 (1996), no. 2 and CIRP Annals. Manufacturing technology 1 (1995)) proposes that the drive system in a processing machine be softly coupled to the base. However, the relative reference between the output-drive section and the reaction section is measured by the measurement system, by means of a linear tacho. The result of the measurement is then supplied to the control unit. This allows the control system to have direct access to the relative movement between the output-drive section (useful mass or tool) and the base, since the movement of the reaction section is superimposed on the movement of the output-drive section, relative to the fixed base. The movement of the reaction section must therefore be corrected numerically in the position data, for which reason the soft coupling of the drive system to the base must have a behavior which is constant and can be defined in absolute terms. Even very minor discrepancies in the coupling parameters lead to major errors in the useful load movement.
SUMMARY OF THE INVENTION
The invention is based on the object of providing a motor of this generic type for machine tools or the like, which is designed such that it can be controlled in a simple manner, particularly without requiring any numerical correction for the movement of the reaction section.
According to one aspect of the invention, the drive motor for a machine tool includes an output-drive section associated with a load, a reaction section which interacts with the output-drive section, a base for attaching the drive motor to the machine tool, a bearing apparatus disposed between the reaction section and the base, with the reaction section mounted on the bearing apparatus such that the reaction section performs a movement that opposes movement of the output-drive section, and a position sensing device for deriving data for position control of the drive motor, wherein the position sensing device determines position data of the output-drive section relative to the base.
The invention is based on the surprising knowledge that precise tool movement control is possible despite the reaction section being decoupled from the base. The consistent use of the characteristics of a direct drive according to the invention, namely power conversion, allows an additional degree of freedom to be derived from this, which allows the predetermined drive momentum to be transmitted to the useful load without the base being loaded by the unavoidable opposing momentum. The present invention makes use of the characteristic that a power converter, such as a synchronous motor with permanent-magnet excitation, converts the feed variable—in this case the current—into a drive force proportional to this feed variable, directly and without any delay. In the case of power converters, such as the synchronous electric motor which is used as an example here, the drive force is dependent essentially only on the feed variable. It is significant that the present position of the motor active surfaces with respect to one another and, above all, their present speed with respect to one another, have no significant influence on the motor power. In high-quality power converters, the position-dependent and speed-dependent influences on the motor power are negligible.
The power converter thus always provides a drive force which is dependent exclusively on the feed variable used at that time, for example the current, but not on the speed or the position of the motor active surfaces. If a drive axis is set up according to the invent
Aguirrechea J.
Feiereisen Henry M.
Mullins Burton S.
Siemens Aktiengesellschaft
LandOfFree
Momentum-decoupled direct drive does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Momentum-decoupled direct drive, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Momentum-decoupled direct drive will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3297452