Electricity: motive power systems – Braking – 'spotting' or adjustment of braking controller during coasting
Reexamination Certificate
2000-03-21
2001-09-18
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Braking
'spotting' or adjustment of braking controller during coasting
C318S362000, C318S364000, C318S368000, C318S374000, C318S379000
Reexamination Certificate
active
06291951
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to a control circuit for a servo-motor D.C. holding brake.
II. Description of the Prior Art
Industrial manufacturing facilities, such as an automotive assembly plant, utilize electric servo-motors to drive some high inertia loads. For example, such electric motors are utilized to drive turrets, framing systems, and the like.
For safety reasons, these servo-motors are equipped with a “holding brake” to prevent any free motion of the system, when the servo-motor controller is disabled. Otherwise, such electric servo-motors could provide free movement of their load and potentially injure the manufacturing equipment, the manufactured item or even maintenance persons working on it.
There have been a number of previously known electric brakes for braking the electric servo-motor in the event of a power failure. Such electric brakes typically include a pair of input terminals which are connected to the power source which also powers the electric motor. Typically, a rectifier as well as a voltage reduction circuit is conventionally interposed between the power supply for the electric motor and the brake input terminals on the electric brake.
These previously known electric brakes maintain the brake in a released condition as long as the power input to the brake is greater than a preset threshold voltage, for example 5-6 volts. However, in the event of a power failure, the voltage input to the brake terminals for the electric brake falls below the preset voltage immediately thus causing the brake to activate and stop the motor.
Although these previously known electric holding brakes have proven effective for stopping the motors in the event of a power failure, in many cases, the load being moved by the electric motor is extremely massive. In these cases, the immediate braking action of the electric motor can result in extremely high torque and other stress imposed on both the motor holding brake as well as the load being moved by the motor. Such excessive forces in some cases are sufficient to not only damage, but also destroy the holding brake and/or transmission.
SUMMARY OF THE PRESENT INVENTION
The present invention provides a holding brake control circuit which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the holding brake control circuit includes a pair of output terminals which are connected to the brake terminals of the electric brake. Similarly, the control circuit includes a pair of power input terminals which are connected to the electric power source and this power source has a voltage greater than the preset voltage necessary to maintain the electric brake in a released condition.
One or more capacitors are connected in parallel with the input terminals so that, during normal operation, the power source both charges and maintains the capacitor in a charged condition.
The control circuit further includes a voltage regulator having input terminals and output terminals. The input terminals are connected in parallel with the capacitor while the output terminals from the voltage regulator are connected in parallel with the brake input terminals.
The voltage regulator is preferably a low drop out voltage regulator such as an NTE 1952 voltage regulator. Furthermore, the regulated voltage output from the voltage regulator is equal to or greater than the voltage necessary to maintain the electric brake in a released condition.
In operation, during normal operation the power supply charges the capacitor and, after charging, maintains the capacitors in a charged condition. Consequently, the voltage input to the voltage regulator is substantially the same, or slightly lower than, the voltage of the power supply. Furthermore, after charging the capacitors, the supply voltage is effectively electronically connected to the brake terminals thus maintaining the electric brake in a released condition.
In the event of a power failure, however, the charging voltage to the capacitors terminates, and the capacitor discharges its accumulated charge through the voltage regulator. In doing so, the charge from the capacitor is able to maintain the output voltage from the voltage regulator to the electric brake at or above the voltage necessary to maintain the electric brake in a released condition for a period of time, e.g. 20 seconds. This relatively long time delay between the time of power failure and the actuation of the electric brake allows the load previously driven by the servo-motor to slow down so that, at the time of brake actuation, the stresses and torque imposed on the motor and load are minimized.
REFERENCES:
patent: 4030007 (1977-06-01), Price et al.
patent: 4348625 (1982-09-01), Sharp
patent: 4754211 (1988-06-01), Karjalainen
patent: 5814956 (1998-09-01), Kono et al.
patent: 6078156 (2000-06-01), Spurr
patent: 6084365 (2000-07-01), Anderson et al.
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Leykin Rita
Nappi Robert E.
Valiant Machine & Tool Inc.
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