US20020121408A1

US20020121408A1 - Control for a pumping system used in association with a machine tool fluid circuit

Info

Publication number: US20020121408A1
Application number: US09/797,010
Authority: US
Inventors: James Youngers
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-03-01
Filing date: 2001-03-01
Publication date: 2002-09-05

Abstract

Output of a fluid supply unit in a fluid circuit associated with a machine tool is controlled by operating a pump motor at a constant speed, maximum in the preferred form of the invention, during the entire fluid supply operation and varying the connection between the motor and a pump to vary the flow conditions, such as flow rate, pressure or the like of fluid being supplied. Pump output is directly related to the degree of coupling in one form of the invention. Accuracy of fluid output response is improved over prior art systems by locating a flow characteristic sensor immediately adjacent to the output of the pump and controlling volume adjacent to the pump output and the flow characteristic sensor so changes in flow conditions are rapidly located adjacent to the flow characteristic sensor.

Description

BACKGROUND OF THE INVENTION

Many machine tools, such as cutting or drilling tools, or the like, require a supply of machining fluid to the work area during a machining operation. The fluid often must pass through small openings in which flow rates may require high pressures. Furthermore, the flow rate of the machining fluid is often subject to change. Still further, one fluid circuit may often supply several machines each of which can have a changing demand. Coupling this with the pressure demands often associated with modem machine tools creates system requirements that are often stringent and difficult to accurately and efficiently satisfy.

One system that has been used in the past includes a variable volume, variable pressure coolant system for use in association with machine tools. Various forms of these systems exist, and include variable speed motors as well as systems that vary flow rate by varying a state condition of the fluid, such as varying the pressure of the flowing fluid.

While somewhat effective, the prior art designs have drawbacks that vitiate the efficiency and effectiveness thereof.

For example, in some modem machining operations, demand for machining fluid can rapidly change. That is, machining fluid flow rates can rapidly increase or decrease, and the machining fluid supply system must react to such changes in a timely, yet accurate manner. Systems that rely on changing the speed of a motor driving a fluid supply pump to change fluid flow rates can decrease motor life and can be wasteful of energy, and may not be accurate or rapid enough to meet the demands of modem technology. Systems that rely on changing flow parameters may be very slow to react to the change in demand, especially when changes are associated with electronically controlled machine tools.

Hence, there is a need for a flow circuit associated with supplying machining fluid to a machine tool during a machining operation which can rapidly yet accurately react to demands and changes in demands for machining fluid. Still further, there is a need for such a system that is energy efficient and does not place an undue amount of stress on any motor used in the system.

Yet another drawback to prior art systems is their tendency to over- or under-shoot the targeted demand requirement. As discussed above, many modern machine tools are electronically controlled. As such, demand can change at speeds associated with electronics; to wit: milliseconds. Such rapid demand changes can place extreme demands on the fluid system to rapidly change.

As is well known, mechanical equipment has inertia which often causes such equipment to have a delay time in reacting to a change in demand and then to overshoot the demand requirement. The delay time slows response time and the overshoot creates a requirement to either slow the equipment or to account for the overshoot possibility by cycling the equipment. This may create either a slow system response time or an overshoot situation or an undershoot situation or both which can, in some extreme cases, create an unstable condition in the flow circuit. At best, such equipment response is wasteful, inaccurate and slow to establish an accurate flow rate, and at worst, it can damage the equipment or the system.

Therefore, there is a need for a flow circuit associated with supplying machining fluid to a machine tool during a machining operation which can rapidly yet accurately react to demands and changes in demands for machining fluid while substantially reducing the possibility of overshooting or undershooting the demand requirement.

The prior art also contains machine tool fluid circuits which include a pump motor controlled by a computer. A flow parameter sensor, such as a pressure transducer, is coupled to a computer which is connected to a pump motor and to a control unit to regulate machining fluid flow.

The computer controlled system has advantages over the just-described systems; however, it also has certain drawbacks including a requirement that the pump motor speed be changed to react to fluid system demands. As discussed above, mechanical devices, such as motors, have inertia and may be slow to react and may tend to over or under shoot the demand requirement. As also discussed above, drawbacks may adversely affect flow accuracy and/or stability.

The inventor has discovered that in addition to the above-discussed reasons an additional reason for inaccurate response to changing flow rate demand is caused by the physical characteristics of the system itself. That is, flow conduit lengths, shapes and conditions may affect the time the flow system takes to react to a change in demand of the machine tool system as well as the manner of that reaction. The physical characteristics of the system may influence the time it takes for a flow condition associated with changed flow conditions to reach a sensor measuring flow parameters and which is being used in the circuit controlling the fluid supply. This time must be accounted for in the control system. Accounting for time lapses between a changed supply and reading that changed supply may be inaccurate and may be subject to several influences that cannot be accounted for in an initial design for the systems controlling the fluid flow of the system.

For example, there may be some distance between an outlet for a fluid supply in the machining fluid flow circuit and a sensor measuring a flow parameter. The parameter being measured often travels at the speed of the fluid flow and thus may take some time to reach the sensor. This delay time can be considerable if there is a great distance between the sensor and the supply outlet, and can be affected by turns in the conduit fluidically connecting the sensor and the supply outlet. This delay adds a factor that must be considered in designing the fluid circuit and the control circuits associated therewith, and as such may lead to inaccuracies.

Therefore, there is a need for a flow circuit associated with supplying machining fluid to a machine tool during a machining operation which is not unduly influenced by system physical characteristics.

SUMMARY OF THE INVENTION

The above-discussed disadvantages and drawbacks are overcome by a fluid system associated with supplying machining fluid to a machine tool in which a pump motor is continuously operated at its maximum speed and the coupling between the motor and its associated pump is changed to vary pump operation in response to fluid system requirements. The preferred form of coupling is magnetic, but, as will be understood from the teaching of this disclosure, other coupling forms can also be used.

In this manner, since the motor is being operated at its maximum all the time, and the only element that must be varied in response to system fluid demand changes is a coupling, time delays associated with elements such as motor speed changes are avoided and pump output can change rapidly. Still further, other of the above-mentioned drawbacks associated with motor speed changes are avoided.

Furthermore, the system embodying the present invention includes a flow control element, such as an orifice, positioned immediately adjacent to the outlet of the fluid supply system and the sensor used to sense flow conditions is also located immediately adjacent to the fluid supply system outlet. The orifice controls flow and flow perturbations and ensures that changes in flow conditions are nearly immediately sensed by the flow condition sensor which is located closely adjacent to the fluid supply outlet for the flow system. Thus, the inaccuracies associated with sensors that are spaced from the supply source are avoided.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the general art of machine tools, and to the particular field of machine tools that include application of a fluent medium to the work area or work product.

OBJECTS AND ADVANTAGES OF THE INVENTION

It is a main object of the present invention to provide a flow circuit associated with supplying machining fluid to a machine tool during a machining operation which can rapidly yet accurately react to demands and changes in demands for machining fluid.

It is another object of the present invention to provide a flow circuit associated with supplying machining fluid to a machine tool during a machining operation which can rapidly yet accurately react to demands and changes in demands for machining fluid.

It is another object of the present invention to provide a flow circuit associated with supplying machining fluid to a machine tool during a machining operation which is no t subject to flow perturbations associated with the physical system located between the flow supply outlet and a sensor used to control that flow supply.

Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.

The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the overall system embodying the present invention for supplying machining fluid to a machine tool. [0023]
FIG. 2 is a block diagram showing one form of the coupling used to variably couple a constant speed motor to a pump in the system of the present invention. [0024]
FIG. 3 shows a coupling of the present invention variably coupling a constant speed motor to a pump to vary the pump output. [0025]
FIG. 4 is a block diagram showing another form of the variable coupling of the present invention. [0026]
FIG. 5 shows a fluid flow control and monitoring system embodying the present invention in which changes in fluid flow parameters are quickly sensed and are not unduly affected by fluid system physical characteristics. [0027]

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. [0028]
As above discussed, many of the problems associated with the prior art are overcome by the system embodying the present invention which operates a pump-driving motor at maximum speed throughout a fluid supplying cycle and varies the pump output in response to changes in demand placed on the fluid supply circuit. This is accomplished by coupling the pump motor to the pump using a variable coupling that is controlled according to the demand placed on the fluid supply circuit whereby the coupling is movable between a coupling position coupling the constant speed motor to the pump in a manner that drives the pump in relation to the maximum speed of the motor and an uncoupled position at which the pump is de-coupled from the motor and thus is idle, with the coupling being variable for varying the degree of coupling between the motor and the pump so the speed of operation of the pump is a function of the degree of coupling between the motor and the pump. [0029]
This is illustrated in FIG. 1 with [0030] system 10 including a constant speed motor 12 variably coupled to a pump 14 by a coupling 16 that is variable and controlled. The control is electrically coupled to a fluid supply system control unit 18 that is also connected to a fluid supply circuit 20 associated with a machine tool (not shown). In FIG. 1, fluid connections are indicated by full lines and electrical connections are indicated by dotted lines.
As discussed above, coupling [0031] 16 is variable between a condition in which the pump is fully coupled to the constant speed motor and a condition in which the pump is completely de-coupled from the motor and does not operate even though the motor is still operating at maximum speed, as well as all conditions in between with the pump operation being a function of the degree of coupling between the motor and the pump. For example, the greater the coupling, the closer the pump will operate to that operation associated with a fully coupled motor and pump (i.e., one hundred percent pump operation).
One form of such a coupling is indicated in FIGS. 2 and 3 as being a [0032] magnetic coupling 26. Magnetic coupling 26 includes a torque tube assembly 32 attached to a hub 34 on an output shaft of motor 12 that always operates at full speed. The motor can start under no-load. A fixed DC coil 36 is attached to a stator which is attached to a main casing 40. When coil 36 is energized, a magnetic flux is established traveling through the stator, casing, torque tube and polewheel 42. Polewheel 42 is fixed to inner end 44 of pump shaft 46. As the magnetic flux passes through the torque tube, the polewheel is attracted to the torque tube. This causes the pump shaft to rotate. A built-in tacho generator 48 provides a linear speed signal to the control unit 18, allowing a closed loop control system to regulate the speed of the pump. One form of magnetic coupling is produced by Torspec, Inc.
As can be seen, by varying the current through [0033] coil 36, the degree of coupling between pump 14 and motor 12 can be varied. As will also be understood, since this coupling is magnetic, the degree of coupling can be changed with speeds associated with electronic speeds. This allows the pump to react to changes in demand from the machine tool fluid system at speeds approximating those of the machine tool demand changes.
While the magnetic coupling is the preferred form of the coupling unit, other forms can be used. These additional forms can include a [0034] hydraulic unit 50 shown in FIG. 4 which includes a hydraulic pump 52 coupled to a hydraulic motor 54 to drive the motor in accordance with pressure from the hydraulic pump. The pressure of the hydraulic pump is controlled by control unit 18 with hydraulic motor 52 also being connected to control unit 18 in a closed loop control system. Operation of the hydraulic pump/hydraulic motor unit is known to those skilled in the art, and will thus not be discussed.
While two types of variable coupling have been disclosed, the coupling can also be comprised of variable pulley drives, clutch drives, chain drives, gear box drives, transmission drives, electrical connections as well as electrical clutch or transmission drives. The exact connection of these couplings between [0035] motor 12 and pump 14 will be understood by those skilled in the art.
As was discussed above, the inventor has discovered that one reason for inaccurate response to changing flow rate demand is caused by the physical characteristics of the system itself. Thus, the present invention controls flow adjacent to the outlet of the pump in a manner such that system physical characteristics will not unduly affect control of the pump. This objective is achieved by arranging the fluid system such that changes in pump output are sensed by the appropriate sensors as quickly as possible after the changed flow condition occurs at the pump outlet. [0036]
This objective is achieved by two structural features of the present invention. First, as shown in FIG. 5, a flow condition sensor, such as a [0037] pressure sensor 60, is positioned closely adjacent to output 62 of pump 14. The close positioning of the flow condition sensor to the pump output will permit the changes in pump output to be very quickly located at the flow characteristic sensor.
However, this is not sufficient to ensure that the flow characteristic sensor senses the exact condition. If there is a large volume adjacent to the sensor, this volume will affect the value of the condition sensed. Thus, the present invention incorporates a second element to reduce the volume adjacent to the pump output and the flow characteristic sensor. In the preferred form of the invention, this second element is a [0038] flow orifice 64 located on the downstream side of the flow characteristic sensor and closely adjacent thereto. The flow orifice is sized to control flow in a manner that confines pressure changes to the area immediate to the pump output and the flow characteristic sensor, yet ultimately permits flow in conduit 66 fluidically connecting pump output 62 to machine tool fluid circuit 20.
In the preferred form of the invention, [0039] orifice 64 has a flow diameter of between 0.125 inch and 0.200 inch, and the flow characteristic sensor is a pressure transducer, WIKA Model No. 8341219 electrically connected to control unit 18 via wires 68. The preferred form of the invention uses a tee connection 70 to couple the pressure transducer and the orifice to the pump output. However, these elements could be directly fluidically connected to the pump output without the tee connection if desired. The tee connection simply permits matching conduit sizes.
It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown. [0040]

Claims

What is claimed and desired to be secured by Letters Patent is as follows:

1. A variable volume and pressure fluid supply system for use with a machine tool comprising:

a motor which operates at a constant speed;

a pump fluidically connected to a fluid circuit of machining fluid used in a machine tool;

a controlled coupling connecting said motor to said pump, said coupling including

a first element connected to said motor to be operated by said motor at the speed of the motor,

a second element connected to said pump to operate said pump, and

a coupling means movable between a coupling position coupling said first element to said second element in a manner that drives said second element at a speed that essentially matches the speed of said motor and an uncoupled position at which said first and second elements are de-coupled from each other, said coupling means having means for varying the degree of coupling between said first and second elements so the speed of operation of said pump is a function of the degree of coupling between said first and second elements.

2. The fluid supply system defined in claim 1 wherein said coupling means includes a magnetic element that is controlled by a magnetic field associated with said magnetic element with an increase in magnetic field strength increasing the speed of the pump toward the speed of the motor.

3. The fluid supply system defined in claim 1 wherein said coupling means includes a hydraulic motor and a hydraulic pump with an increase in hydraulic pump pressure increasing the speed of said pump toward the speed of said motor.

4. The fluid supply system defined in claim 1 further including a fluid pressure sensor positioned in the output line of said pump.

5. The fluid supply system defined in claim 4 further including a fluid flow control element positioned in the output line of said pump upstream of a fluidic connection between said pump and the fluid circuit.

6. The fluid supply system defined in claim 5 wherein said fluid flow control element includes a flow orifice.

7. A method of supplying machining fluid to a machine tool comprising:

using a pump, pumping machining fluid to a machine tool based on demand of the machine tool;

driving the pump using a motor;

operating the motor at maximum speed for essentially the entire pumping step;

variably coupling the motor to the pump; and

varying the coupling between the pump and the motor to vary the flow of the machining fluid to the machine tool.

8. The method defined in claim 7 wherein the step of varying the coupling between the pump and the motor includes varying the a magnetic force associated with the coupling.

9. The method defined in claim 7 further including a step of using an orifice to control flow out of the pump.

10. The method defined in claim 9 further including positioning a flow sensor immediately adjacent to the outlet of the pump and immediately adjacent to the orifice.