DESC:FIELD OF INVENTION

The present invention relates to a system for monitoring the coolant drain in a machine tool. In particular, the invention relates to a system for online monitoring of the coolant drain. More particularly, the invention relates to the coolant drain detection by flow control in a spindle motor failure on a machine tool.

BACKGROUND OF THE INVENTION

In any machine tool, high-pressure coolant is used for cooling the machine tool and for providing lubrication while machining. This coolant pressure is usually of the order of 25 bar, which is quite high and it often happens that this high-pressure coolant reaches the spindle motor of the machine tool. Here, due to improper sealing, it may enter the spindle motor and seriously damage it. For example, in horizontal multi-axis machining center, such as Makino a61 & Makino a61nx Production Machining Center, latest machine technologies are available which provide a higher level of productivity, accuracy and machine reliability for manufacturing parts, particularly, producing automotive parts. However, frequent spindle motor failures are observed due to the ingress of the high-pressure coolant inside the spindle motor.

PRIOR ART

In such horizontal machining centers, normally a high pressure coolant is used during machining operation for overall coolant application on machine for all the tools used in machining operations. A maximum coolant pressure used is about 25 bar. When tool is clamped, the tool holder is engaged in spindle by means of draw bar mechanism. The tool holder holds the coolant tube, which sit in place by means of special seals provided inside the draw bar. The machine manufacturer normally provides a fixed amount of coolant drain in the spindle mechanism to avoid coolant ingress into the spindle motor. On opening the drain, coolant goes to coolant tank by gravity. This is a normal phenomenon in the integrated spindle on horizontal machine centers.

DISADVANTAGES WITH THE PRIOR ART

At present, there is no control check provided for ascertaining the proper sealing or for checking the availability of coolant tubes provided on machine. Hence, there is leakage of high pressure coolant from the rotary coolant joints and due to human error, non-use of coolant tubes in tool holder creates excess coolant in a compartment and this leaked coolant enters inside the spindle motor and bearings. Further, same excess coolant flows through the drain to coolant tank.

The ingress of leaked coolant inside the spindle is a serious cause of spindle motor failure and leads to deterioration of the spindle motor and bearings.

Therefore, there is a need for improving the coolant supply and monitoring system in such machine tools, whereby the coolant drain in a machine tool is properly monitored, particularly by means of an online coolant drain monitoring system, whereby the coolant drain leakage is detected and controlled by a coolant flow control system for safeguarding the spindle motor in a machine tool.

OBJECTS OF THE INVENTION

Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:

An object of the present invention is to provide a coolant monitoring system for a machine tool used for mass production of machined components.

Another object of the present invention is to provide a coolant leakage monitoring system to detect any coolant leakage into spindle motor of a machine tool used for mass production of machined components.

Still another object of the present invention is to provide coolant leakage monitoring system working online to prevent any coolant leakage into spindle motor of a machine tool used for mass production of machined components.

Yet another object of the present invention is to provide an online coolant monitoring system in a machine tool manufacturing high volume machined components to avoid frequent spindle failure.

A still further object of the present invention is to provide an online coolant detecting and measuring system in a machine tool to precisely control the coolant flow therein.

Yet further object of the present invention is to provide online coolant detection and display system in a machine tool to indicate excessive coolant leakage to the spindle motor for immediately stopping machine tool for prevent spindle failure.

These and other objects and advantages of the present invention will become more apparent from the following description, when read with the accompanying figures of drawing, which are however not intended to limit the scope of the present invention in any way.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a coolant drain detection and measurement system fitted on the coolant flow circuit in a machine tool, the system comprising:

• a spindle provided with a plurality of sealing rings at predetermined locations thereon and also provided with a rotary joint at the one end and a coolant tube with a special coolant seal at the other end thereof;
• a three-port ejector assembly;
• a coolant spindle with the first end thereof connecting the coolant line to the ejector assembly and the second end thereof to a coolant tube provided with a special coolant seal;
• a coolant valve connected to the three-port ejector assembly at one end thereof and to the coolant tank bottom level at the other end thereof;
• an air-supply unit connected to a fist solenoid and via a coolant valve;
• a coolant tank; and
• a coolant drain detection and measurement system fitted between the coolant drain under the spindle and the coolant tank via a second solenoid.

Typically, the system comprises a compact programmable logic controller (PLC) with Human Machine Interface (HMI) and a low-flow sensor and a low-flow adaptor for determining the normal designed coolant leakage rate and the continuously monitoring the coolant draining from the machine spindle; wherein an alarm is issued by the system by glowing light emitting diodes (LEDs) or by sounding an alarm when the coolant leakage rate is determined to be three times the normal specified leakage rate, indicating the leakage of the coolant in the rotary joint .

Typically, a high precision coolant media flow transducer (SI 5004) is provided as the sensor positioned inside the moving slide of the machine.

Typically, an analog output of the transducer in the range of 4–20 mA is configured with the PLC mounted in an easily accessible area for easy and complete monitoring of the coolant flow rate and thereby any coolant leakage present in the spindle motor.

Typically, the sensor is configured for a coolant flow of 0-25 litre per minute.

Typically, the PLC supporting two analog inputs in a range of 0-20 mA and 0-10 V each, converts the output of the flow-sensor into a digital value for monitoring and programming of the coolant flow rate.

Typically, the resolution of the analog input is 14 bits provided with an embedded Human Machine Interface (HMI).

Typically, the sealing rings are provided at a predetermined position along the length of machine spindle and the first sealing ring is a rotating sealing ring and the second sealing ring is a fixed sealing ring.

Typically, one of the ports of the three-port ejector assembly is connected to the coolant tank via the coolant valve and the remaining one port each is connected to the spindle and pressure valve respectively.

In accordance with the present invention, there is also provided a method for online monitoring of the coolant drain for detecting coolant drainage into the spindle motor, the method comprises the steps of:

• continuously checking the coolant flow from the machine spindle and exiting through the coolant drain;

• comparing the coolant flow from the coolant drain with the normal coolant leakage rate to determine the spindle motor health;

• issuing an audible (sound) or visible (LEDs) alarm to the machine operator, if the coolant leakage rate is detected to be above three times the specified normal coolant leakage rate or if there is no coolant tube on the tool holder;

• stopping the machine the immediately once the alarm is detected; and

• detecting the location of the coolant leakage and repairing the same before restarting the machine.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be briefly described with reference to the accompanying drawings, wherein:

Figure 1 shows a perspective rear view of the conventional arrangement with a coolant gravity drain on the machine spindle of the machine tool, i.e. without any coolant leakage detection system;

Figure 2 shows a perspective view of the coolant drain detection and measurement system configured in accordance with the present invention on the machine spindle of the machine tool.

Figure 3 shows a schematic diagram of the in the coolant flow circuit of the machine tool configured with the innovative coolant drain detection and measurement system in accordance with the present invention.

Figure 4 shows a typical compact Unitronics V350 PLC with HMI and low-flow sensor incorporated in the coolant drain detection and measurement system in accordance with the present invention.

Figure 5 shows the displays generated by the device shown in Figure 4 showing actual coolant leakage into the spindle motor and the limits thereof for the machine operator’s use.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the following, the online coolant drain detection and measurement system for in accordance with the present invention will be described in more details with reference to the accompanying drawings without limiting the scope and ambit of the present invention in any way.

Figure 1 shows a perspective rear view of the conventional arrangement 50 having a coolant drain working by gravity as provided in the machine spindle of the horizontal axis machine tools. So, there is no provision for a coolant leakage detection and measurement system in this arrangement 50. This leads to frequent spindle motor failure because of excessive coolant leakage into the spindle motor.

Figure 2 shows a perspective view of the innovative coolant drain detection and measurement system 150 configured on the machine spindle of the machine tool. This incorporates a low-flow sensor and adaptor with a Unitronics Programmable Logic Control (PLC) for coolant flow detection and measurement, which displays the actual coolant leakage into the spindle motor and its limits for educating the machine operator to take timely action by stopping the machine to avoid any spindle motor failure in case of excessive coolant leakage into the spindle motor.

Figure 3 shows a schematic diagram of the in the coolant flow circuit of the machine tool configured with the innovative coolant drain detection and measurement system 150 configured in accordance with the present invention. The horizontal axis machine tool 100 includes a machine spindle 102, a rotary joint 104 at the one end thereof and a coolant tube 108 provided with a special coolant seal 110 at the other end thereof. A rotating sealing ring 112 and a fixed sealing ring 114 are provided at a predetermined position along the length of machine spindle 102. A coolant line 106 connects one end (right side end in this figure) of the coolant spindle 102 to an ejector assembly 118. One end of the coolant valve 124 is connected to an air unit 116 and the other end of the coolant valve 124 is connected to a solenoid SOL1306. One of the ports of the 3-port ejector assembly 118 is connected to the coolant tank 126 via the coolant valve 124, the other ports being connected to the spindle 102 and pressure valve P respectively. Since the machine manufacturers do not provide any such coolant drain and detection and measurement system, in order to avoid the spindle motor failure due to ingress of coolant inside spindle motor, the coolant drain leakage detection and measurement system 150 is configured in accordance with the present invention and suitably provided on the machine spindle cartridge. The system 150 is connected between the coolant drain 122 leading from the machine tool spindle 102 towards the coolant tank 126 via another solenoid SOL1309. The valve P is provided for measuring the coolant pressure in the coolant tank 126. The innovative coolant detection and measurement system 150 includes a low-flow sensor 120, an analog output 128 to PLC and a low-flow adaptor 130 inside the IMF 132. This system 150, for example uses a compact Unitronics V350 PLC with Human Machine Interface (HMI) and an IMF low-flow sensor 120 and a low-flow adaptor 130 for deciding the normal designed coolant leakage rate. The system 150 continuously checks the coolant draining from the machine spindle 102 and thereby ascertains the health of the spindle motor. If the coolant leakage rate is detected to be above (e.g. 3 times), which is the normal leakage rate specified by the machine manufacturer, an alarm is issued by the system 150 either by glowing LEDS or by sounding an alarm to the machine operator. This alarm provides an early signal to indicate that there is a leakage of coolant in the rotary joint 104 or shows the non-availability of the coolant tube 106 on the tool holder. As soon as the alarm is issued, the machine stops running. The fault is detected and repaired and only them the machine will be restarted. This helps in avoiding the expensive spindle motor replacement costing around INR 8.5 lacs. In case of a complete damage to the spindle cartridge, this cost may be as high as INR 17.5 lacs, which is a substantial cost to the organization, apart from loss of operating hours due to the long repair schedule of a defective spindle motor or replacement of the defective spindle cartridge. The coolant drain leakage detection and measurement system 150 configured in accordance with the present invention is very easy and cost-effective and thereby provides substantial cost savings.

Figure 4 shows a typical compact Unitronics V350 PLC with HMI and low-flow sensor incorporated in the coolant drain detection and measurement system in accordance with the present invention. This is provided with a high precision coolant media flow transducer SI 5004. The sensor is positioned inside the moving slide of the machine. For easy monitoring of the coolant leakage in the spindle motor, 4–20 mA analog output of the transducer is configured with the PLC or Controller mounted in an easily accessible area for complete monitoring of the coolant flow rate. The sensor can be configured for a coolant flow of 0-25 litre per minute. The Unitronics Vision 350 PLC converts the output of the above flow-sensor into a digital value for monitoring and programming purposes. This PLC supports 2 analog inputs of 0-20 mA and 0-10 V each. The resolution of the analog input being 14 bits (while a normal PLC provides only 10 bits resolution for analog input). Unitronics V 350 PLC comes with an embedded HMI (Human Machine Interface).

Figure 5 shows the displays generated by the device shown in Figure 4 showing actual coolant leakage into the spindle motor and the limits thereof for the machine operator’s use. It shows both the spindle coolant leakage and spindle coolant leakage limit in mL/min. It also indicates the “Dwell time for an Alarm”.

Implementation of the PLC with HMI:

The resolution in bits is the digital scale to which analog input can be converted. For example, in a PLC with a 14 bit analog input resolution, a 0-20 mA analog value can be converted into 2 ^14 = 16384. This means, a 0-20 mA scale will be converted into digital value of 0 to 16384.

Whereas, in a PLC with 10 bit resolution, the equivalent measurable scale would have been: 2^10= 1024. This means, a 0-20 mA scale will be converted into digital values of 0 to 1024 only. It is already known that higher resolution means more accurate readings.

Conversion factor:

Output of transducer = 4 to 20 mA

Input to transducer = 0 to 20 mA

So, for zero flow: Input = 4 mA.

Thus, the corresponding change in value/mA => 16384/20 = 819.2

For a 4 mA reading: 819.2 x 4 = 3276.8

Digital value for a 4 to 20 mA reading = 3276.8-16384.

A special adapter is made for low flow coolant leakage detection. By using this adapter, the flow transducer can detect coolant leakage in a range of 0 to 1 Litres per minute, so it will output 20 mA for a coolant leakage of 1 litre per minute.

Flow meter scale setting in HMI:

Digital value for a 4 to 20 mA reading = 3276.8-16384

Total range = 16384 - 3277(~3276.8) = 13107

So, the scale is set as 0 to 1000 ml/min.

Value for 1000 ml = 13107

Therefore, change in value for each ml/min change => 13107/1000= 13.1

This concept of On-line coolant drain detection and measurement system for integrated spindles motor was never used before on any machine. This system facilitates in providing an early alarm system to avoid the spindle motor failures frequently occurring on machines used for mass production of components, e.g. automotive components. This enhances the service life of the critical components of the machine tools by strengthening their predictive maintenance.

TECHNICAL ADVANTAGES & ECONOMIC SIGNIFICANCE

Some of the technical advantages of the On-line coolant drain detection and measurement system in accordance with the present invention used for integrated spindles motor on machine tools for manufacturing mass-production of machined components are as under:

• Avoids frequent spindle motor failures.
• Dispenses with spindle motor replacement costing around INR 8.5 lacs.
• Obviates substantial expenditures of the order of about INR 17.5 lacs in case of a complete damage to the spindle cartridge.
• Saves substantial costs due to the loss of operating hours of the machine.
• Helps in avoiding production delays due to time spent on spindle motor repair or for replacing the damaged spindle cartridge.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, shall be understood to implies including a described element, integer or method step, or group of elements, integers or method steps. However, it does not imply excluding any other element, integer or step, or group of elements, integers or method steps. In the claims and the description, the terms “containing” and “having” are used as linguistically neutral terminologies for the corresponding terms “comprising”.

The use of the expression “a”, “at least” or “at least one” shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention. Furthermore, the use of the term “one” shall not exclude the plurality of such features and components described.

The description provided herein is purely by way of example and illustration. The various features and advantageous details are explained with reference to this non-limiting embodiment in the above description in accordance with the present invention.

The descriptions of well-known components and manufacturing and processing techniques are consciously omitted in this specification, so as not to unnecessarily obscure the specification. In the previously detailed description, different features have been summarized for improving the conclusiveness of the representation in one or more examples.

However, it should be understood that the above description is merely illustrative, but not limiting under any circumstances. It helps in covering all alternatives, modifications and equivalents of the different features and exemplary embodiments. Many other examples are directly and immediately clear to the skilled person because of his/her professional knowledge in view of the above description.

Therefore, innumerable changes, variations, modifications, alterations may be made and/or integrations in terms of materials and method used may be devised to configure, manufacture and assemble various constituents, components, subassemblies and assemblies according to their size, shapes, orientations and interrelationships.

While considerable emphasis has been placed on the specific features of the preferred embodiment described here, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiments without departing from the principles of the invention.

These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

The exemplary embodiments were selected and described in order to be able to best represent the principles and their possible practical application underlying the invention. Thereby, the skilled persons can optimally modify and use the invention and its different exemplary embodiments with reference to the intended use. ,CLAIMS:We claim:

1. A coolant drain detection and measurement system fitted on the coolant flow circuit in a machine tool, the system comprising:

• a spindle provided with a plurality of sealing rings at predetermined locations thereon and also provided with a rotary joint at the one end and a coolant tube with a special coolant seal at the other end thereof;
• a three-port ejector assembly;
• a spindle with the first end thereof connecting the coolant line to the ejector assembly and the second end thereof connected to a coolant tube provided with a special coolant seal;
• a coolant valve connected to the three-port ejector assembly at one end thereof and to the coolant tank bottom level at the other end thereof;
• an air-supply unit connected to a fist solenoid and via a coolant valve;
• a coolant tank; and
• a coolant drain detection and measurement system fitted between the coolant drain under the spindle and the coolant tank via a second solenoid.

2. Coolant drain detection and measurement system as claimed in claim 1, the system comprises a compact programmable logic controller (PLC) with Human Machine Interface (HMI) and a low-flow sensor and a low-flow adaptor for determining the normal designed coolant leakage rate and the continuously monitoring the coolant draining from the machine spindle; wherein an alarm is issued by the system by glowing light emitting diodes (LEDs) or by sounding an alarm when the coolant leakage rate is determined to be three times the normal specified leakage rate, indicating the leakage of the coolant in the rotary joint .

3. Coolant drain detection and measurement system as claimed in claim 1, a high precision coolant media flow transducer (SI 5004) is provided as the sensor positioned inside the moving slide of the machine.

4. Coolant drain detection and measurement system as claimed in claim 3, an analog output of the transducer in the range of 4–20 mA is configured with the PLC mounted in an easily accessible area for easy and complete monitoring of the coolant flow rate and thereby any coolant leakage present in the spindle motor.

5. Coolant drain detection and measurement system as claimed in claim 4, wherein the sensor is configured for a coolant flow of 0-25 litre per minute.

6. Coolant drain detection and measurement system as claimed in claim 5, wherein the PLC supporting two analog inputs in a range of 0-20 mA and 0-10 V each, converts the output of the flow-sensor into a digital value for monitoring and programming of the coolant flow rate.

7. Coolant drain detection and measurement system as claimed in claim 6, wherein the resolution of the analog input is 14 bits provided with an embedded Human Machine Interface (HMI).

8. Coolant drain detection and measurement system as claimed in anyone of the claims 1 to 7, wherein the sealing rings are provided at a predetermined position along the length of machine spindle and the first sealing ring is a rotating sealing ring and the second sealing ring is a fixed sealing ring.

9. Coolant drain detection and measurement system as claimed in anyone of the claims 1 to 7, wherein one of the ports of the three-port ejector assembly is connected to the coolant tank via the coolant valve and the remaining one port each is connected to the spindle and pressure valve respectively.

10. A method for online monitoring of the coolant drain for detecting coolant drainage into the spindle motor, the method comprises the steps of:

• continuously checking the coolant flow from the machine spindle and exiting through the coolant drain;
• comparing the coolant flow from the coolant drain with the normal coolant leakage rate to determine the spindle motor health;

• issuing an audible (sound) or visible (LEDs) alarm to the machine operator, if the coolant leakage rate is detected to be above three times the specified normal coolant leakage rate or if there is no coolant tube on the tool holder;

• stopping the machine the immediately once the alarm is detected; and

• detecting the location of the coolant leakage and repairing the same before restarting the machine.

Dated: this 25th day of March, 2015. SANJAY KESHARWANI
APPLICANT’S PATENT AGENT