Patent Application
20090093191
This invention relates to grinding machines, and in particular, to control circuits for grinding machines.
A grinding machine typically employs a grind wheel that is formed from an abrasive material or that has an abrasive material thereon. To perform a grinding operation, the grind wheel is generally caused to rotate via a motor. Once the grind wheel is rotating at a desired rate, the grind wheel contacts a workpiece to perform a grinding operation. Industrial grinding machines may have a variety of features such as a cover for the grind wheel to protect a user from contact with the grind wheel or from debris thrown off the workpiece by the grind wheel. Another common feature is a feed arm, which engages the workpiece and is used to advance the workpiece into contact with the grind wheel and, in some embodiments, to withdraw the workpiece from the grind wheel. By manipulating the feed arm, a user can grind a workpiece while keeping the user's hands away from the grind wheel.
Centerless grinding machines typically employ two wheels, a grind wheel and a regulating wheel, between which is disposed a work-support blade. In use, the grind wheel and the regulating wheel are both driven by respective motors, and a workpiece is disposed in position for grinding by being placed on the work-support blade and in contact with the grind wheel and the regulating wheel. In some centerless grinding machines, the grind wheel rotates in a fixed position, and the regulating wheel is mounted on a movable feed arm and is movable by means of a lead screw attached to the feed arm. The feed arm (and, therefore, the regulating wheel) is movable between an advanced position and a retracted position. In the advanced position, the regulating wheel engages a workpiece, causes the workpiece to engage the grind wheel, and controls the pressure and the difference in rotational speed between the grind wheel and the workpiece. In the retracted position, the regulating wheel permits the workpiece to disengage from the grind wheel and to be removed from the grinding machine. The regulating wheel may otherwise be moveable to facilitate removal of the workpiece from the grinding position, or to facilitate maintenance on the grind wheel, or for other reasons. Coolant, cutting fluid, or the like may be flowed to the grind wheel and/or to the regulating wheel to prevent overheating and/or to transport debris away from the grind wheel. A grinding machine may have several motors, including a hydraulic motor, which maintains an adequate pressure in a hydraulic system for creating a fluid film of oil for the grind wheels' hydrostatic bearings which creates a clearance between moving and stationary components; a coolant pump motor for pumping coolant to the grind wheel and/or to the regulating wheel; a grind wheel motor for driving the grind wheel; and a regulating wheel motor for driving the regulating wheel.
In some prior art grinding machines, once the grind wheel has been set in motion, the grind wheel is not stopped to load or unload workpieces. Similarly, in some prior art centerless grinding machines, once the grind wheel and the regulating wheel have been set in motion, they are not stopped to load or unload workpieces. Such grinding machines are initially energized by actuating a master power switch, and in some cases the grind wheel is caused to rotate by actuating the master power switch a second time, as long as the required hydraulic pressure has been reached for the hydraulic system.
Based on the foregoing, it is the general object of this invention to provide a control circuit for a grinding machine that improves upon prior art grinding machines.
The present invention resides in one aspect in a logic circuit for a grinding machine. The logic circuit includes inputs for a signal from a WHEEL START switch and for a sensor signal from each of one or more sensors selected from the group consisting of a feed arm sensor, a hydraulic pressure sensor, a wheel guard sensor, and a coolant sensor. Each said sensor providing a sensor signal that indicates a condition of the grinding machine. The logic circuit also includes an output for connection to a grind wheel motor. The logic circuit is configured to respond to actuation of the WHEEL START switch by initiating a WHEEL START logic operation that comprises initiating operation of the grind wheel motor after receiving a predetermined sensor signal from at least one of said one or more sensors.
The present invention resides in another aspect in a control circuit for operating a grinding machine. The control circuit includes a power-on switch, one or more sensors selected from the group consisting of a feed arm sensor, a hydraulic pressure sensor, a wheel guard sensor, and a coolant sensor, each said sensor providing a sensor signal that indicates a condition of the grinding machine, a WHEEL START switch, and a logic circuit. The logic circuit is configured to receive a signal from the WHEEL START switch and a sensor signal from said one or more sensor, and to generate a wheel start signal only when the signal from the first sensor satisfies a precondition to operating the grinding machine. The control circuit includes an output for connection to a grind wheel motor.
The present invention resides in another aspect in a grinding machine that comprises a control circuit, a grind wheel and a grind wheel motor that is responsive to the control circuit for operating the grind wheel, and a movable feed arm for advancing a workpiece to the grind wheel. There is a feed arm sensor for the feed arm, capable of generating a signal to indicate whether the feed arm has been retracted. The control circuit is responsive to the feed arm sensor, such that when the grinding machine is started, the control circuit does not initiate operation of the grind wheel motor or the regulating wheel motor unless the feed arm sensor indicates that the feed arm is retracted.
In a specific embodiment, the invention relates to a centerless grinding machine that comprises a control circuit, a grind wheel and a grind wheel motor that is responsive to the control circuit for operating the grind wheel, a movable feed arm, a regulating wheel on the feed arm, and a regulating wheel motor that is responsive to the control circuit, for operating the regulating wheel. The feed arm is movable between an advanced position, in which the regulating wheel can engage a workpiece and cause such workpiece to engage the grind wheel, and a retracted position, in which the regulating wheel permits said workpiece to disengage from the grind wheel. There is a feed arm sensor for the feed arm, capable of generating a signal to indicate whether the feed arm is in the retracted position, and the control circuit is responsive to the feed arm sensor. When the grinding machine is started, the control circuit does not initiate operation of the grind wheel motor or the regulating wheel motor unless the feed arm sensor indicates that the feed arm is in the retracted position.
This invention provides a control circuit for a grinding machine that incorporates several features that are not found in prior art grinding machines and that can be provided independently of each other, or in various combinations. The control circuit includes one or more sensors and switches, and the control circuit controls working components of the grinding machine such as the grind wheel motor. The control circuit includes a logic circuit that makes operation of one or more working components contingent upon receipt of predetermined signals from one or more of the sensors and/or switches.
A grinding machine that incorporates a control circuit as described herein is shown schematically in
The grinding machine 10 has a control circuit 70 (shown in
The control circuit 70 comprises a user-operable POWER ON switch 42 (
From a cold start, operation of the grinding machine 10 and the control circuit 70 begins with actuation of the POWER ON switch 42. A set-up period follows actuation of the POWER ON switch 42. During the set-up period, a user performs set-up tasks to prepare the grinding machine 10 for grinding. The set-up tasks may include actuating various switches and positioning the feed arm 24 and the wheel guard 26 as needed. For example, the user may set the COOLANT OPERATION selector switch 52 to the desired setting, and actuate the COOLANT switch 50. The WHEEL SELECTOR switch 56 is set to “BOTH” and the speed of the regulating wheel may be set as desired via the REGULATING WHEEL SPEED potentiometer 54. During the set-up period, the sensors generate signals indicating the condition of their associated components. After the set-up tasks have been performed, the WHEEL START switch 46 is actuated.
The control circuit 70 includes a logic circuit 62 (
After start-up, the logic circuit 62 permits ongoing operation of the grinding machine 10 even when the feed arm 24 moved out of the retracted position to advance the regulating wheel to the workpiece (not shown) and the signal from the feed arm sensor 28 is no longer being generated.
Optionally, either the WHEEL START logic operation or the ongoing operation of the grinding machine 10, or both, may be contingent on a signal from one or more other sensors and/or switches. For example, the start-up and/or ongoing operation of the grind wheel motor 12 and the regulating wheel motor 16 may be contingent on a signal from a hydraulic pressure sensor 30 that indicates that the pump of the hydraulic system is providing adequate fluid pressure. Other optional contingencies for start-up and/or ongoing operation may be whether the coolant pump 22 is providing adequate coolant pressure, as indicated by a coolant sensor 34, and/or whether the wheel guard 26 be in position to protect the user, as sensed by a wheel guard sensor 32.
Optionally, the control circuit 70 may be configured so that once the grind wheel 14 has begun operating, the control circuit will stop both the grind wheel and the regulating wheel 18 should a stop condition occur. The grind wheel 14, which generally has higher inertia and rotational velocity (RPM) than the regulating wheel 18, is preferably moderately braked to a stop. One stop condition is caused by actuation of a WHEEL STOP switch 48 by the user. Another possible stop condition occurs when the feed arm sensor 28 indicates that the feed arm 24 has returned to the retracted position. Stopping both the grind wheel 14 and the regulating wheel 18 is safer than stopping only one of them or allowing them to continue running while a workpiece is being loaded or unloaded. By providing a dynamic braking system as disclosed herein, improved safety is achieved without significant burden on the operator and without significant increase in production time. Other optional stop conditions may include loss of hydraulic pressure, loss of coolant pressure, untimely retraction of the wheel guard 26, etc., all as indicated by suitable sensors. To restart the wheels for the next grinding operation, the user must actuate the WHEEL START switch 46 again.
Optionally, the control circuit 70 is responsive to an EMERGENCY STOP switch 60. The EMERGENCY STOP switch 60 is easily operable by a user to quickly shut down the operation of the grinding machine 10. Upon actuation of the EMERGENCY STOP switch 60, the control circuit 70 may cut off power to any or all of the components of the grinding machine 10.
The control circuit 70 may optionally provide for automatic control of coolant, thereby reducing the chances of coolant flowing to a stopped wheel. Proper control of the coolant saves on operating costs by reducing electricity consumed, prolongs the use of the motor that drives the wheel, and reduces the quantity of mist expelled into the work environment.
In some embodiments, a control circuit 70 as described herein employs relays to abruptly send current to the grind wheel motor 12 and the regulating wheel motor 16, which causes frequent closing of the contacts in these motors. Alternatively, a “soft start” control, or a speed control, for the grind wheel motor may be employed. A soft start control would add slower “ramped up” starts for the grind wheel motor 12 and would produce less shock to the grind wheel motor and the grind wheel motor drive train than relays. Optionally, a “Variable Frequency Drive” (VFD) can be provided to allow the user to control the rotational speed of the regulating wheel 18 by manipulating the REG WHEEL SPEED potentiometer 54. The VFD (not shown) may also be wired and/or programmed to automatically change the rotational speed of the regulating wheel 18 to a preset value for dressing, as indicated when the WHEEL SELECTOR switch 56 is set to operate only the regulating wheel.
In a specific embodiment, the grinding machine 10 is equipped with a dynamic brake (not shown) that is responsive to the control circuit 70. Such dynamic brakes are known in the art and are commercially available, such as the Baldor™ BQ8 Dynamic Brake. For a normal (i.e., non-emergency) wheel stop, the dynamic brake allows for fairly quick stopping of the grind wheel 14, for safer part loading and unloading, without adversely affecting production time, or causing undue wear to the grinding machine 10. Optionally, the EMERGENGY STOP switch 60 may be wired directly to a specialized input on the dynamic brake to allow for a fast stop of both the grind wheel 14 and the regulating wheel 18 without need for a stop signal from the control circuit 70.
In a particular embodiment, the control circuit 70 includes one or more optional fault indicators that the control circuit will activate if selected sensors indicate a “fault condition”, i.e., a condition that does not conform to a pre-selected or preprogrammed parameter such as motor overloads, low hydraulic pressure, etc. The fault condition may be a stop condition and/or the absence of a condition contingent for the WHEEL START logic operation or contingent for ongoing operation of the grinding machine 10. A fault indicator may be visual or auditory in nature, e.g., the indicator may be a signal light (such as an LED) or a buzzer. The control circuit 70 may be programmed to halt the operation of the grinding machine 10 when a fault condition occurs. After attending to the fault condition, the user can actuate a FAULT RESET switch 58 to re-initiate the control circuit 70 and attempt to resume normal operation of the grinding machine 10. Optionally, a fault indicator (not shown) may be built into the FAULT RESET switch 58. Upon actuation of the FAULT RESET switch 58, the logic circuit 62 again executes the WHEEL START logic function before resuming operation of the grinding machine 10.
One embodiment of a control circuit 70 as described herein is shown in
An alternative control circuit 70a is shown in
In addition, in the control circuit 70a of
The logic circuit 62 is programmed to control the grinding machine components connected thereto (e.g., motors 12, 16, 20, 22) by issuing signals to those components according to a logic function based on the input signals received. One embodiment of such a logic function is depicted in
If, upon actuation of the WHEEL START switch 46, the WHEEL START logic function detects that one or more preconditions are not satisfied, a FAULT alert is provided to the user, who may then remedy the situation. For example, if the feed arm sensor 28 indicates that the feed arm 24 is not in the retracted position, the logic circuit 62 will not power the grind wheel motor 12 or the regulating wheel motor 16, and will instead generate a FAULT alert (e.g., the logic circuit 62 may illuminate a FAULT alert LED (not shown) that may be built into the FAULT RESET switch 58). After the user remedies the fault, the user actuates a FAULT RESET switch 58. The logic circuit 62 responds to the FAULT RESET switch 58 by re-executing the WHEEL START logic function.
Once the grinding machine 10 is in operation, the logic circuit 62 permits ongoing operation until a stop condition is sensed. When a stop condition is sensed, the operation of the grinding machine 10 is stopped (the grind wheel motor 12 and the regulating wheel motor 16 are de-energized and the appropriate brakes are applied to the grind wheel 14 and the regulating wheel 18). The logic circuit 62 may be configured or programmed to distinguish between routine stop conditions, which may be followed by the user actuating the WHEEL START switch again, and other fault-type stop conditions which lead to the generation of a FAULT alert. One routine stop condition may be movement of the feed arm 24 to the retracted position when a part is ready to be removed from the grinding machine 10. A fault-type stop condition may be a hazardous condition, for example, the retraction of the wheel guard 26 while the grind wheel 14 is being driven.
In alternative embodiments of the control circuit 70, the logic circuit 62 may comprise a logical hard-wired system instead of being programmable, although hard-wired systems take more time to construct, are more costly, harder to modify or upgrade, and are more difficult to troubleshoot than are programmable circuits. Also, an alternative control circuit for a grinding machine as described herein need not have all of the sensors and switches that are included in the illustrated control circuit 70. Instead, any one or more of the sensors and/or switches shown herein, and/or other sensors and/or switches, or any combination thereof, may be employed.
Furthermore, the control circuit 70 and method of operation described herein is applicable to various types of grinding machines and grinding processes, including so-called centerless plunge grind or in-feed grind operations, as well as grinding machines that are not centerless grinding machines. In some of such other grinding machines lack a regulating wheel, and have a feed arm that engages a workpiece and advances a workpiece into engagement with the grind wheel for grinding, instead of advancing a regulating wheel. However, such grinding machines can employ the other features (sensors, switches, control circuit, etc.) described herein for the centerless grinding machine 10.
The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. In addition, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
Although the invention has been described with reference to particular embodiments thereof, it will be understood by one of ordinary skill in the art, upon a reading and understanding of the foregoing disclosure, that numerous variations and alterations to the disclosed embodiments will fall within the spirit and scope of this invention and of the appended claims.
This application claims the benefit of U.S. provisional application No. 60/977,737 filed Oct. 5, 2007, which is hereby incorporated herein by reference, in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60977737 | Oct 2007 | US |
