Patent Publication Number: US-2022235985-A1

Title: Cooling system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 110102483 filed in Taiwan (R.O.C.) on Jan. 22, 2021, the entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The disclosure relates to a cooling system, more particularly to a cooling system that can offer a gas of stable temperature. 
     BACKGROUND 
     In the field of machine tool, metal or other rigid materials can be machined by cutting, boring, grinding, shearing, or other forms of deformation. Using cutting tool at high rotational speed. Generally, machine tools employ some sort of tool that does the cutting or sharping to a workpiece. Regarding the boring or drilling machine tool, their cutting tools can be rotated at an extremely high speed, thus unwanted material can be removed from the workpiece during the relative movement between the workpiece and the cutting tool. However, during the machining process, high temperature often appears at the rotating shaft that rotates the cutting tool or the workpiece. This may lead to thermal expansion of the shaft or other material around, affecting the machining accuracy. 
     Thus, a refrigeration circulation is used to cool down the shaft of the machine tool. In the typical refrigeration circulation, the cooling capability is adjusted by regulating the frequency of the compressor, and the shaft or other high-temperature materials can be cooled using cooled fluid. When the cooling requirement is lowered, the frequency of the compressor is decreased as well. When the frequency of the compressor is decreased to the minimum frequency, the compressor is turned off but only will be turned on as long as there is a cooling requirement again. 
     This type of operation results in repeatedly turning on and off the compressor, thus the temperature of the cooled fluid is unstable. As a result, the shaft temperature of the machine tool becomes unstable, affecting the machining accuracy. 
     SUMMARY 
     Accordingly, the present disclosure provides a cooling system that can avoid repeatedly turning on and off the compressor so as to offer cooling gas of stable temperature to machine tool and therefore improve the machining accuracy. 
     One embodiment of the disclosure provides a cooling system configured for cooling a machine tool. The machine tool has a machine temperature. The cooling system comprises a gas source, a refrigeration circulation, a fan, and a controller. The gas source is configured for providing a gas. The refrigeration circulation comprises a heat exchanger, a compressor, a condenser, and an expansion valve. The heat exchanger is in fluid communication with the gas source and is configured to cool the gas down to a target temperature and to provide the gas to the machine tool. The compressor has an operation frequency. The fan is configured to cool the condenser and has a rotation speed. The controller is connected to the compressor and the fan. When a target temperature difference that is equal to the machine temperature minus the target temperature is smaller than a threshold temperature difference, the controller keeps the operation frequency at a minimum frequency and sets the rotation speed to be smaller than a maximum rotation speed. 
     According to the cooling system as discussed in the above embodiments of the disclosure, when the target temperature difference is smaller than the threshold temperature difference, the operation frequency of the compressor is maintained at the minimum frequency and the rotation speed of the fan is set to be smaller than the maximum rotation speed, such that the compressor is able to continuously operate without being turned off. Also, the reduction of the rotation speed of the fan can make the cooling system more applicable to smaller target temperature difference. Therefore, the cooled gas will have a stable temperature, and the temperature of the machine tool will be stable as well, improving the machining accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become better understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not intending to limit the present disclosure and wherein: 
         FIG. 1  is a block diagram of a cooling system according to one embodiment of the disclosure; and 
         FIG. 2  is a flow chart showing the operation of the cooling system in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. 
     Referring to  FIG. 1 , there is shown a block diagram of a cooling system according to one embodiment of the disclosure. 
     The cooling system  1  is able to cool down a machine tool  9 , where the machine tool  9  has a machine temperature T m . In this embodiment, the cooling system  1  includes a gas source  2 , a refrigeration circulation  3 , a fan  4 , a controller  5 , a pressure regulator valve  6  and a supplying module  7 , but the disclosure is not limited thereto. The cooling system in another embodiment may omit the pressure regulator valve  6 . 
     In this embodiment, the gas source  2  is provided to offer a gas (e.g., air). The refrigeration circulation  3  includes a heat exchanger  31 , a compressor  32 , a condenser  33 , and an expansion valve  34 . A suitable coolant is flowing in the refrigeration circulation  3 . The compressor  32  has an operation frequency F c  during operation. The fan  4  is to help move unwanted heat away from the condenser  33 . The fan  4  has a rotation speed R f  during operation. 
     In this embodiment, the heat exchanger  31  has a first pipe  311  and a second pipe  312  that are in thermal contact with each other. The first pipe  311  is in fluid communication with the gas source  2  so as to cool the gas down to a target temperature T a . The second pipe  312  is in fluid communication with the compressor  32  and the expansion valve  34 , where the coolant flows through the second pipe  312 . 
     In this embodiment, the controller  5  is electrically connected to the compressor  32  and the fan  4 . The controller  5  is able to control the operation frequency F c  of the compressor  32  and the rotation speed R f  of the fan  4 . 
     In this embodiment, the pressure regulator valve  6  is connected to the first pipe  311  of the heat exchanger  31 . The controller  5  is connected to the pressure regulator valve  6 . The controller  5  is able to control the pressure regulator valve  6  in order to regulate the pressure of the gas to a target pressure P t . The first pipe  311  is able to provide the cooled gas to the pressure regulator valve  6  and the supplying module  7  so as to offer it to the machine tool  9 , but the disclosure is not limited thereto. In other embodiments, the heat exchanger  31  may directly provide the cooled gas to the machine tool  9 . 
     In this embodiment, the supplying module  7  includes a storage tank  71 , a pump  72 , a mixing valve  73 , and a throttle valve  74 . The storage tank  71  is configured to store a lubricating fluid. The pump  72  is connected to the storage tank  71 . The pump  72  is to pump the lubricating fluid out of the storage tank  71 . The mixing valve  73  is connected to the first pipe  311  of the heat exchanger  31  via the pressure regulator valve  6 . In addition, the mixing valve  73  is connected to the pump  72 . The throttle valve  74  is connected to the mixing valve  73 . The controller  5  is electrically connected to the pump  72  so as to control the pump  72 , such that the lubricating fluid can be provided to the mixing valve  73  at specific time interval I. The mixing valve  73  is al be to mix the gas coming from the heat exchanger  31  and the lubricating fluid coming from the pump  72 . The throttle valve  74  is able to provide the machine tool  9  with the mixture of the gas and the lubricating fluid. In this embodiment, the mixing valve  73  is connected to the heat exchanger  31  via the pressure regulator valve  6 , but the disclosure is not limited thereto. In other embodiments, the mixing valve  73  may be directly connected to the heat exchanger  31 . 
     Referring to  FIGS. 1 and 2 , there is shown a flow chart of the operation of the cooling system  1 . The operation of the cooling system  1  may contain the following steps: 
     In step S 01 , the cooling system  1  is in stand-by mode. In this mode, the compressor  32  of the refrigeration circulation  3  and the fan  4  were turned off by the controller  5 . In addition, by the controller  5 , the target pressure P t  is set at a predetermined minimum value using the pressure regulator valve  6 . Also, the controller  5  sets the specific time interval I to a predetermined maximum value for the later process of pumping the lubricating fluid out of the storage tank  71  and offering it to the mixing valve  73 . The cooled gas and the lubricating fluid is mixed by the mixing valve  73 . The throttle valve  74 , as discussed above, is able to offer the mixture of the gas and the lubricating fluid to the machine tool  9 . In one embodiment, the predetermined minimum value of the target pressure P t  may be 1.5 bar, and the predetermined maximum value of the specific time interval I may be 180 seconds. 
     Then, in step S 02 , the machine tool  9  outputs a signal related to shaft rotation speed R m . The controller  5  receives the signal of the shaft rotation speed R m . 
     Then, in step S 03 , the controller  5  determines whether the shaft rotation speed R m  is zero (i.e., determining whether R m =0). When the controller  5  determines that the shaft rotation speed R m  is zero (i.e., R m =0), the operation goes back to step S 01 . This result means that the machine tool  9  is not in operation, and the cooling system  1  is still in stand-by mode. On the other hand, when the controller  5  determines that the shaft rotation speed R m  is not zero (i.e., R m ≠0), then step S 04  is performed. Note that the value of the rotation speed is always in positive value, thus when R m ≠0, meaning R m &gt;0. 
     In step S 04 , the machine tool  9  outputs signals related to the shaft rotation speed R m , shaft load L, and the machine temperature T m . When the controller  5  determines that the shaft rotation speed R m  is not zero (i.e., R m &gt;0), the controller  5  receives the signals of the shaft load L and the machine temperature T m  of the machine tool  9 . In this embodiment, the controller  5  is able to repeatedly receive the signal of the shaft rotation speed R m  so as to timely detect the condition of the machine tool  9 , but the disclosure is not limited thereto. In other embodiments, the controller  5  may not repeatedly receive the signal of the shaft rotation speed R m . 
     Then, in step S 05 , the controller  5  calculates target temperature difference ΔT and target temperature T a  according to the signal of the shaft rotation speed R m , the shaft load L, and the machine temperature T m . The shaft rotation speed R m  is positively proportional to the target temperature difference ΔT. The shaft load L is positively proportional to the target temperature difference ΔT. In specific, the target temperature difference ΔT satisfies the following relations: ΔT=aR m   2 +bR m +cR m L, wherein ΔT denotes the target temperature difference, a, b, c denote positive coefficients, R m  denotes the shaft rotation speed, L denotes the shaft load. In addition, the target temperature difference ΔT is equal to the machine temperature T m  minus the target temperature T a . That is, T a =T m −ΔT. In one embodiment, a=4×10 −8 , b=2×10 −8 , c=5×10 −8 . The target temperature difference ΔT, machine temperature T m  and the target temperature T a  are measured in degrees Celsius(° C.). The shaft rotation speed R m  is measured in RPM (revolutions per minute). The shaft load L (%) is equal to the current output power of the machine tool  9  divided by predetermined maximum output power. 
     Then, in step S 06 , the controller  5  determines whether the target temperature difference ΔT is equal to a threshold temperature difference ΔT t  (i.e., determining whether ΔT=ΔT t ). When the controller  5  determines that the target temperature difference ΔT is equal to the threshold temperature difference ΔT t  (i.e., ΔT=ΔT t ), then step S 07  is performed. On the other hand, when the controller  5  determines that the target temperature difference ΔT is not equal to the threshold temperature difference ΔT t  (i.e., ΔT≠ΔT t ), then step S 08  is performed. 
     In step S 07 , the target temperature difference ΔT is equal to the threshold temperature difference ΔT t  (i.e., ΔT=ΔT t ), the controller  5  sets the operation frequency F c  of the compressor  32  at the minimum frequency F a  (i.e., controlling the compressor  32  by setting F c =F ct ), and the controller  5  sets the rotation speed R f  of the fan  4  at maximum rotation speed R ft  (i.e., controlling the fan  4  by setting R f =R ft ). In one embodiment, the minimum frequency F ct  may be 35 Hz (i.e., F ct =35 Hz), but the disclosure is not limited thereto. In other embodiments, the minimum frequency F ct  may be adjusted according to the type of the compressor  32 . 
     In step S 08 , the target temperature difference ΔT is not equal to the threshold temperature difference ΔT t  (i.e., ΔT≠ΔT t ), the controller  5  determines whether the target temperature difference ΔT is greater than the threshold temperature difference ΔT t  (i.e., determining whether ΔT&gt;ΔT t ). When the controller  5  determines that the target temperature difference ΔT is greater than the threshold temperature difference ΔT t  (i.e., ΔT&gt;ΔT t ), then step S 09  is performed. On the other hand, when the controller determines that the target temperature difference ΔT is neither greater than nor equal to the threshold temperature difference ΔT t  (i.e., ΔT&lt;ΔT t ), then step S 10  is performed. 
     In step S 09 , the target temperature difference ΔT is greater than the threshold temperature difference ΔT t  (i.e., ΔT&gt;ΔT t ), the controller  5  sets the operation frequency F c  of the compressor  32  to be larger than the minimum frequency F a  (i.e., controlling the compressor  32  by setting F c &gt;F ct ), and sets the rotation speed R f  of the fan  4  at the maximum rotation speed R ft  (i.e., controlling the fan  4  by maintaining R f =R ft ). The operation frequency F c  is positively proportional to the target temperature difference ΔT (i.e., controlling the compressor in a way of keeping the operation frequency F c  to be proportional to the target temperature difference ΔT). 
     In step S 10 , the target temperature difference ΔT is smaller than the threshold temperature difference ΔT t  (i.e., ΔT&lt;ΔT t ), the controller  5  sets the operation frequency F c  of the compressor  32  at the minimum frequency F a  (i.e., controlling the compressor  32  by maintaining F c =F ct ), and sets the rotation speed R f  of the fan  4  to be smaller than the maximum rotation speed R ft  (i.e., controlling the fan  4  by setting R f &lt;R ft ). The rotation speed R f  is positively proportional to the target temperature difference ΔT (i.e., controlling the fan  4  in a way of keeping the rotation speed R f  to be proportional to the target temperature difference ΔT). By doing so, when the target temperature difference ΔT is smaller than the threshold temperature difference ΔT t , the compressor  32  is able to continuously operate without being turned off; that is, there is no need to repeatedly turn on and off the compressor  32 . Accordingly, the coolant flowing through the second pipe  312  of the heat exchanger  31  will have a stable temperature. 
     Step S 11  is performed after steps S 07 , S 09  or S 10 . In step S 11 , the heat exchanger  31  cools the gas coming from the gas source  2 . In specific, the coolant flowing through the second pipe  312  of the heat exchanger  31  is able to absorb heat contained in the first pipe  311  of the heat exchanger  31 . This can reduce the temperature of the gas down to the target temperature T a . Due to the stability of the coolant flowing over the second pipe  312 , the coolant is able to stably cool the gas within the first pipe  311 , such that the cooled gas will have a stable temperature as well. 
     Also, the controller  5  calculates the target pressure P t  according to the shaft rotation speed R m  and the shaft load L. The shaft rotation speed R m  is positively proportional to the target pressure P t . The shaft load L is positively proportional to the target pressure P t . The target pressure P t  satisfies the following relation: P t =dR m   2 +eR m +fL+g, where P t  denotes target pressure, d, e, f, g denote positive coefficients. In one embodiment, d=3×10 −9 , e=1×10 −5 , f=0.005, g=1.5. The target pressure P t  is measured in bar. The shaft rotation speed R m  is measured in RPM. The shaft load L (%) is equal to the current output power of the machine tool  9  divided by predetermined maximum output power. The controller  5  controls the pressure regulator valve  6  to set the pressure of the gas to be the target pressure P t . In one embodiment, 1.5 bar≤P t ≤4.0 bar. 
     Further, the controller  5  calculates the specific time interval I according to the shaft rotation speed R m  and the shaft load L. The shaft rotation speed R m  is positively proportional to the specific time interval I, while the shaft load L is negatively proportional to the specific time interval I. The specific time interval I satisfies the following relation: I=hR m   2 +iR m −jL+k, where I denotes specific time interval, h, i, j, k denote positive coefficients. In one embodiment, h=1×10 −7 , i=6×10 −4 , j=0.4, k=100. The specific time interval I is measured in second. The shaft rotation speed R m  is measured in RPM. The shaft load L (%) is equal to the current output power of the machine tool  9  divided by predetermined maximum output power. The controller  5  controls the supplying module  7  so as to supply the mixture of the gas and the lubricating fluid to the machine tool  9  at specific time interval I. In specific, the controller  5  controls the pump  72  so as to provide the lubricating fluid to the mixing valve  73  at the specific time interval I, the mixing valve  73  mixes the cooled gas and the lubricating fluid, and then the throttle valve  74  offers the mixture of the gas and the lubricating fluid to the machine tool  9 . Due to the stability of the cooled gas, the mixture of the gas and the lubricating fluid will have a stable temperature as well, making the temperature of the machine tool  9  stable and helping improve the machining accuracy  9 . 
     In this embodiment, the controller  5  calculates the target pressure P t  and the specific time interval I during step S 11 , but the disclosure is not limited thereto. In other embodiments, the controller  5  may calculate the target pressure P t  and the specific time interval I during any one of the steps from S 05 -S 10 . 
     Lastly, step S 12  is performed after step S 11 , in step S 12 , the controller  5  determines whether the cooling system  1  is turned off. When the controller  5  determines that the cooling system  1  is turned off, the operation of the cooling system  1  is stopped. On the other hand, when the controller  5  determines that the cooling system  1  is still on, then the operation goes back to step S 02 . 
     According to the cooling system as discussed in the above embodiments of the disclosure, when the target temperature difference is smaller than the threshold temperature difference, the operation frequency of the compressor is maintained at the minimum frequency and the rotation speed of the fan is set to be smaller than the maximum rotation speed, such that the compressor is able to continuously operate without being turned off. Also, the reduction of the rotation speed of the fan can make the cooling system more applicable to smaller target temperature difference. Therefore, the cooled gas will have a stable temperature, and the temperature of the machine tool will be stable as well, improving the machining accuracy. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure. It is intended that the specification and examples be considered as exemplary embodiments only, with a scope of the disclosure being indicated by the following claims and their equivalents.