Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
2002-09-11
2004-01-27
Duda, Rina I. (Department: 2834)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
C318S567000, C318S568120, C318S569000, C318S600000, C340S500000, C340S541000
Reexamination Certificate
active
06683432
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a safety circuit that monitors a number of sensors for intrusion of objects or people into the workspace of a robot and controls the drive power to the motion control system via an emergency-stop circuit.
BACKGROUND OF THE INVENTION
Safety switches or safety sensors serve for shutting off drive power to machinery when people or objects enter a designated work place zone. Typically, a safety switch is connected to the door or opening that provides access to the work place zone. The safety switch is typically tripped when the door is opened, shutting off drive power to the machinery. Devices of this type are used to prevent people or objects from entering the work place zone while the machine is in operation, decreasing the potential for injury and/or damage to the machinery. Other non-tactile-type intrusion sensors are infrared or ultrasonic, whose sensing zone could be a light curtain or fence, or it could be a quadrant or cone. Typically, drive power to machinery is removed when intrusion is detected, which requires a skilled operator to restart the machinery. Frequently occurring nuisance trips can defeat the advantages of having an automatic machine doing unattended or mundane tasks such as automated refueling for automobiles, because the store attendant is forced to frequently come outside to restart drive power. (It is generally accepted that a consumer is not qualified to restart drive power.)
In an industrial controls environment, presence sensing device initiation (PSDI) is a mode of operation where an intrusion sensor acts as a safeguarding device, but it is also used in a control configuration such that intrusions are monitored so that the “control starts a robot cycle when the sensing field is clear without the need of pressing any additional cycle enable or run buttons” (ANSI/RIA R15.06/1999). This is used to safeguard an operator who is feeding parts to a robot for processing. It is a mode of operation used to start motion for an imminent robot cycle. So far, it lacks sufficient details for implementation, specifically regarding inhibiting motion during the operator's intrusion.
There are a number of patents in this field including U.S. Pat. Nos. 4,263,647; 5,451,879; 4,616,216; 5,263,570; 4,912,384; 5,319,306; 5,278,454; 5,426,355; 4,481,449; 5,880,954; 4,818,866; 4,898,263; 5,280,622; 6,173,814; 4,437,089; 5,218,196; 5,408,089, all of which are incorporated herein by reference. Also incorporated herein by reference is U.S. Pat. No. 6,392,318 entitled “Programmable Emergency-Stop Circuit.”
All references cited herein are incorporated by reference in their entirety, to the extent not inconsistent with the explicit teachings set forth herein.
BRIEF SUMMARY OF THE INVENTION
The safety circuit of the subject invention provides a means for monitoring a number of sensors for intrusion of objects or people into the workspace of a robot, monitors the motion control system, and controls the drive power to the motion control system via an emergency-stop circuit. The safety circuit navigates between permitting the machine to move, inhibiting it for Level 2 Intrusions (precautionary type), and killing drive power for Level 1 Intrusions (serious type). Such navigation establishes a methodology for automated recovery from precautionary situations.
Now, there is a need for a machine to remove drive power when an intrusion incident becomes serious but to automatically recover from cleared precautionary intrusion incidents without requiring a skilled operator's deliberate action. There is a need to provide a framework for implementing this functionality.
At a minimum, such a machine consists of an emergency-stop circuit, at least one intrusion sensor, a safety circuit, and a motion control system that is responsible for effecting the motion to carry out the machine's function. When necessary to avoid the most hazardous situation, the safety circuit kills drive power by utilizing a control signal to the emergency-stop circuit, which in turn stops the flow of bulk power to the motion control system. The emergency-stop circuit also possesses a second, independent interface to start and stop this flow of bulk power.
Accordingly, it is the first object of the invention for the safety circuit take over parts of the motion control system from time to time with the purpose of stopping and disabling motion for each axis but permitting bulk power to remain flowing (HALT state), where the safety circuit subsequently releases control back to the motion control system sometime thereafter (ACTIVE state) so that productivity may resume.
To make further use of this, it is the second object of the invention to provide the safety circuit with at least one intrusion sensor, such that from the sum of all intrusion sensors, the safety circuit can determine the severity of a single or multiple intrusion incidents, where it decides whether the intrusion is severe or precautionary. Here, the safety circuit continues scrutiny for a precautionary intrusion incident in case it becomes severe.
To make further use of this, it is the third object of the invention for the safety circuit when in an ACTIVE state to take over when an intrusion incident occurs so that all axes are stopped (HALT state), to remain in the HALT state if any incident is precautionary but no incident is severe, to kill drive power when an incident is severe (KILLED state), and to release control back to the motion control system if all incidents clear thereby enabling automatic recovery (ACTIVE state). It is the further object of the invention for the safety circuit after entering the KILLED state to remain in the KILLED state until drive power is restarted (ACTIVE state) and while in the KILLED state to force drive power off when an intrusion is sensed and to not force drive power off after all intrusions have cleared. It is the further object of the invention for the safety circuit to enter a KILLED state when drive power is lost as sensed by the safety circuit (e.g. emergency-stop button utilized) or prior to the 1
st
energizing cycle after logic is first powered.
It is the fourth object of the present invention for the safety circuit to emit a visual and/or audible signal when in the HALT state to alert an intruder that productivity is halted.
It is the fifth object of the present invention to model the motion control system as a sensor in order to detect continuously that proper motion control is being conducted. Here, the complex motion control system is considered “potentially unsafe”, but the safety circuit's subsequent monitoring renders the overall system “safe”. When properly operating, the “sensor” reports status to demonstrate that the motion control system can definitely control, move, stop, disable, enable each axis of the machine and also definitely handle the case when an axis has a “motion control fault” (e.g. disabling feedback that stops motion when an axis exceeds an error limit or a limit switch trips due to accidental, controlled movement passed a positional limit).
It is the sixth object of the invention for the safety circuit to declare a “safety circuit fault” when uncertain of the proper operation of the motion control system or any other sensor such that a hazardous situation may exist. The safety circuit kills drive power and enters the ERROR state. While in the ERROR state, it continues to force drive power off, and it remains in the ERROR state until the fault is logged and corrected, if necessary, at which time it returns to the KILLED state.
When motion control system does have full control of the axes (ACTIVE state), a first scenario for risk assessment is in effect, which considers a person is safely outside the workspace of the machine but further considers he may enter the workspace at any time. During this time, normal machine movements and processing are carried out. Here, the assessment considers it hazardous when the safety circuit senses an uncertainty in the location, velocity, or force of an axis (e.g. bad sensor), d
Christine Q, McLeod of Beusse Brownlee Wolter Mora & Maire
Duda Rina I.
Eigenpoint Company
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