Data processing: generic control systems or specific application – Specific application – apparatus or process – Robot control
Reexamination Certificate
1998-09-01
2001-08-28
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Robot control
C700S101000, C700S102000, C700S111000, C700S121000, C318S568100, C318S568120, C318S568160, C318S568210, C414S217000, C414S227000, C414S730000, C414S941000, C235S462150, C235S375000, C438S220000, C438S231000
Reexamination Certificate
active
06282459
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the detection of physical interference during transport of an article and, more specifically, to a structure and method for detection of robot handling errors.
BACKGROUND OF THE INVENTION
Robotic devices are used in many processes for transport of articles in predetermined paths. For instance, robots are used in semiconductor manufacturing to perform tasks such as selecting semiconductor wafers from carrier cassettes, placing them in process chambers, moving them between process chambers, and placing them back into cassettes for transport to a subsequent operation. These robots must operate at very high speeds to assure that tool throughput is not limited by wafer transport, but must also place wafers at their desired location within fractions of a millimeter in three-dimensional space. Because of these requirements, robots used in semiconductor manufacturing are taught the locations for picking up, transporting, and depositing wafers, and are expected to consistently maneuver precisely among those locations repeatedly for months at a time.
If wafers are misplaced by even a small amount, several handling errors are possible. These errors may become evident by some type of physical interference during wafer transport. The wafer may scrape or hit a tool or cassette surface, resulting in either broken wafers or scratched wafer surfaces that ruin any chips at the scratched location. In addition, the robot may cause impact collisions between the wafer and tool surfaces that are too slight to break wafers, but are sufficient to nick the wafer edge. These nicked wafers are then highly likely to break during high-stress process steps such as the polish or heat treatment steps. Finally, the robot itself may be the source of physical interference via rubbing at a joint or on a tool surface, resulting in elevated levels of foreign material particulate matter that may lead to decreased wafer yield and lower productivity.
No real-time method is available to determine if misaligned wafer placement is causing scratches or collisions, or to determine if the robot is rubbing against a surface and causing particulate generation. Periodic foreign material checks will not catch an intermittent problem or find a problem that is just beginning. Because often the same type of robot is used on multiple types of process tools, it is difficult to determine which robot is responsible once a problem has been identified. This difficulty is exacerbated if the problem is intermittent.
Several systems are known for sensing or preventing robot handling errors, including the use of force sensors, strain gauges, or limit switches on the robot arm. Such systems are capable of detecting large or forceful collisions. They cannot detect, however, the very slight physical interference produced by gently scratching or nicking the wafer on a tool surface, or by rubbing at the robot joints.
It is also known to mount active acoustic or light-radiation devices on robots to actively generate a “visual” map of the robot environment, from which the robot makes navigation decisions and avoids collisions. Such systems require a great deal of resources dedicated to active monitoring and mapping. They still may not detect slight physical interference, however, such as rubbing of parts of the robot not within the field of “vision.”
The use of magnetic fields created by placing magnetic strips in the robot arm and in the tool area, and using a field sensor to detect abnormalities in a previously characterized field pattern, has also been used to sense collisions. Such a pattern may not detect slight physical interference between wafers and work surfaces, however, because the relationship between the robot and the tool may be essentially the same for a non-interfering motion and a slight interfering motion. Also, the specific set-up required for mapping every robot motion and every robot geometry is time-consuming and expensive.
In view of the shortcomings of the known systems, there remains a need for an improved structure and method for detection of robot handling errors.
SUMMARY OF THE INVENTION
To meet this and other needs, and in view of its purposes, the present invention provides a method and associated system for using an acoustic sensor, such as an accelerometer, to detect the acoustic signal produced by physical interference with desired transport of an article being moved by a transport device through a predetermined path, such as a wafer being handled by a robot in a workstation. Specifically, the present invention provides a method for detecting physical interference with desired transport of an article, the method comprising:
a) detecting with an acoustic sensor an operative acoustic signal representing a structure-borne sound pattern of the article during transport; and
b) detecting the presence of physical interference based on the acoustic signal;
wherein the acoustic sensor is in structure-borne acoustic contact with the article at least during the physical interference.
The invention also comprises a method for detecting physical interference with desired transport of an article when the article is moved by a transport device through a predetermined path, the method comprising:
a) storing a reference acoustic signal;
b) detecting a subsequent operative acoustic signal representing the structure-borne sound pattern of an article during its transport through the predetermined path;
c) comparing the operative acoustic signal with the reference signal; and
d) detecting any differences between the reference signal and the operative signal and using the detected differences to determine the presence of interference during transport.
Step (a) may further comprise detecting a baseline acoustic signal representing the sound pattern generated during the transport of a sample article through the predetermined path without any physical interference and storing the baseline acoustic signal as the reference acoustic signal.
The method steps for detecting such physical interference may be performed by a system comprising:
a) a transport device adapted to transport the article through a predetermined path; and
b) an acoustic sensor capable of producing an acoustic signal indicative of the physical interference, wherein the acoustic sensor is in structure-borne acoustic contact with the article at least during the physical interference.
The present invention also comprises a program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to perform method steps for detecting physical interference with desired transport of an article when the article is moved by a transport device through a predetermined path, the method steps comprising:
a) inputting and storing a baseline acoustic signal representing the structure-borne sound pattern generated during the transport of a sample article through the predetermined path without any physical interference;
b) inputting a subsequent operative acoustic signal representing a structure-borne sound pattern of an article during its transport through the predetermined path;
c) comparing the operative acoustic signal with the baseline signal; and
d) detecting any differences between the baseline signal and the operative signal and using the detected differences to identify the physical interference.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.
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Wang et al., an Automated Loading and Unloading System for a Maglev wa
Ballantine Arne W.
Fisch Emily E.
Warren Ronald A.
Cuchlinski Jr. William A.
International Business Machines - Corporation
Leas, Agent James M.
Marc McDieunel
Ratner & Prestia
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