Brakes – Inertia of damping mass dissipates motion
Reexamination Certificate
1998-11-09
2001-10-02
Oberleitner, Robert J. (Department: 3613)
Brakes
Inertia of damping mass dissipates motion
C267S136000
Reexamination Certificate
active
06296093
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the area of active vibration control systems, and more particularly, to methods for reducing vibration in machines.
BACKGROUND OF THE INVENTION
Many machines with moving components are subject to vibration. For example, when a machine including a cantilevered beam moveable in space relative to a stationary frame (such as a gantry robot) is abruptly stopped and started, the beam will undergo transient vibrations due to its inertia and inherent flexibility. In cases where there is a machine tool mounted on the beam for performing useful work, vibration of the beam can be translated into unwanted vibration of the machine tool. This, of course, may be translated into poor work quality and/or having to slow the manufacturing process to allow time for such transient vibrations to settle.
Various methods have been used in an attempt to reduce vibration in machines having moveable components, such as robots. For example, joint sensors have been used to determine position and overshoot of the various drive motors and thereby the position and overshoot of robot arms. The drive motors are then appropriately driven by a feedback control method to attempt to minimize system vibration. Such systems which attempt to control vibration via actuation of the drive motors tend to be costly. Generally, this is because in order to achieve the responsiveness needed, very costly drive motors must be utilized. Moreover, these systems may not very effective because the response of the motors, in many cases, is not sufficient to control transient overshoot vibrations. Moreover, such systems may tend to wear significantly over time.
Several prior references are generally directed towards inertial actuators and controlling vibration in pipes or machines. For example, U.S. Pat. No. 5,209,326 to Harper entitled “Active Vibration Control” teaches attaching inertial actuators to a pipe
23
to control vibration caused by a vibrating diesel engine in communication with the pipe. The control utilized is a feedforward algorithm that takes a signal
31
from the diesel engine and signals from sensors
27
,
28
to produce output signals to drive inertial actuators
15
. U.S. Pat. No. 5,251,863 to Gossman et al. entitled “Active Force Cancellation System” teaches a system for controlling vibrations in machines whereby an inertial actuator
4
is secured to a flexible foundation
3
, collocated with a sensor
5
, and aligned along the line of action of the disturbance (the vibrating machinery
1
). U.S. Pat. No. to Stetson entitled “Self Tuning Motion/Vibration Supression System” teaches a sensor
32
and proof mass actuator
52
preferably collocated on a mast
26
. The proof mass actuator
52
is vibrated according to an “integrated motion energy signal” to maintain the integrated signal of the mast at a minimum. U.S. Pat. No. to Forward et al. describes “Wideband Electromagnetic Damping Of Vibrating Structures.” The system includes a sensor
201
for sensing vibration of the structure, a control system
202
and an inertial driver
203
for providing damping forces to damp vibration in the structure. The control utilizes the sum of velocity and acceleration as feedback. Accordingly, none of the above-mentioned patents are directed to systems where the vibrating component undergoes gross motions and transient vibrations resulting therefrom. U.S. Pat. No. 5,102,289 to Yokoshima et al. entitled “Damper Device For Precision Assembling Robot” teaches attaching a passive damper device at the end of the robot arm to absorb vibrations thereof. This systems however, is only effective at a singular frequency and is therefor inefficient in systems where the arm length changes. Moreover, even in systems with unchangeable length arms, the natural frequency of the system can change when the position of the tip of the arm moves in space. A paper given at the Fifth NASA/DOD Controls-Structures Interaction Technology Conference by Raymond Montgomery et al. entitled “Evaluation of Inertial Devices for the Control of Large, Flexible, Space-based Telerobotic Arms,” 1993, describes a system for controlling robot arm vibration by controlling a torque wheel having a reaction mass rotatably mounted thereon. However, such torque motors tend to be expensive, require sophisticated controls, and have a tendency to wear when subjected to such constantly reversing loading.
Therefore, there is a long felt, and unmet, need for a simple, rugged and cost effective vibration-damped machine and method where such machines include a beam moving in space relative to a stationary frame, thereby desirably increasing quality and/or manufacturing throughput.
SUMMARY OF THE INVENTION
In light of the advantages and drawbacks of the prior art, the present invention is a vibration-damped machine and method therefor. More particularly, the vibration-damped machine comprises a beam, such as a cantilever beam, being capable of gross movements in space relative to a stationary frame, means including a motor for causing the beam's gross movements in at least one direction; the gross movements tending to induce vibration into the beam, sensor means for providing at least one signal representative of the induced beam vibration, at least one beam mounted inertial actuator, and control means for receiving the signal and generating an output signal thereby actively driving the linear-acting inertial actuator at the appropriate phase, frequency and magnitude to damp the beam's induced vibration. In several embodiments, it is most preferable to mount both the work member and the linear-acting inertial actuator adjacent to an end of the beam. In those embodiments, the sensor means preferably includes an accelerometer substantially collocated with said at least one inertial actuator. Preferably also, a second sensor is provided which is spaced apart from said first sensor. The second sensor may be located on an intermediate frame member and provides a signal representative of the beam's gross motion.
In a pivoting robot embodiment, the sensor means includes a rotational sensor, and more preferably, also includes a linear sensor substantially collocated with the inertial actuator. The rotational signal from the rotational sensor is transformed into a signal representative of a gross velocity at a location of the linear sensor. The signal representative of gross velocity is subtracted from a signal derived from said linear sensor to generate a signal representing the beam's vibrational velocity. The work member may be a machine tool adapted to machine a work piece, such as in a gantry robot or horizontal milling machine, a fluid dispenser adapted to apply fluid, such as an adhesive, to a work piece such as in a adhesive dispensing machine, or a manipulator adapted to manipulate a work piece, such as in a robot.
According to the invention, vibration-damped machine may include a plurality of inertial actuators, which may be mounted orthogonal, each having a primary vibration axis for controlling multi-axis vibrations.
According to the invention, the control means further comprises an inertial damping control method which forces the linear-acting inertial actuator to behave as though the linear-acting inertial actuator were a damper attached to ground. Preferably, the control method is a function of a tuning mass and spring stiffness of the at least one inertial actuator.
According to the invention, a method is also provided for damping vibration in a machine having a beam being capable of gross motion in space relative to a stationary frame, means including a motor for causing the gross motion of the beam in at least one direction, the gross motion tending to induce vibration in the beam, and a work member mounted to the beam, the method comprising the steps of: providing at least one signal representative of the beam's induced vibration, mounting at least one linear-acting inertial actuator to the beam, processing the at least one signal and generating at least one output signal, and actively driving
Margolis Donald L.
Meyers Andrew D.
Norris Mark A.
Lord Corportion
Nguyen Xuan Lan
Oberleitner Robert J.
Wayland Randall S.
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