Patent Publication Number: US-2023135223-A1

Title: Linear transmission device with capability of real-time monitoring of amount of lubricant

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a linear transmission device, and more particularly, to a linear transmission device with capability of real-time monitoring of an amount of a lubricant. 
     2. Description of the Prior Art 
     Linear transmission devices, such as ball screws or linear guideways, are widely applied in various machines that require precise movement due to their excellent mechanical transmission efficiency. However, elements of the linear transmission devices need sufficient lubrication, or the service life of the linear transmission devices tends to be shortened due to the wear caused by the frictions between the elements. 
     Taiwan patent with Pat. No. I359237 discloses a lubricant sensor apparatus for a ball screw, wherein a nut is externally connected with two wires. The two wires constitute a circuit to conduct electricity. The two wires bring contact resistance through the nut, balls and a screw. When the grease on the balls uses up, the circuit to conduct electricity will be able to form an open circuit so as to activate an alarm device, which reminds the user to pour or replace lubricant. However, the peripheral apparatus of the aforementioned patent is more complicated, and the detection mechanism thereof tends to be affected by working environment, such as cutting fluid and chips, and is not accurate. 
     US patent with U.S. Pat. No. 6,216,821 B1 discloses a lubricating apparatus for a ball screw, wherein a polymer member containing a lubricant is capable of slidably contacting with an outer diameter portion of a screw shaft, which can prevent the lubricant attached to thread grooves of the screw shaft from being scraped off, such that the lubricant can be efficiently maintained in the thread grooves of the screw shaft. However, the aforementioned patent lacks a detecting and feedback mechanism for the remaining amount of the lubricant. When the remaining amount of the lubricant is insufficient or the lubricant is about to exhaust, users cannot know immediately, which is unfavorable for maintenance. 
     As the applied industries of the linear transmission devices, such as semiconductor or automation industries, have entered or are moving towards the field of unmanned factories, how to effectively monitor the amount of the lubricant of the linear transmission devices in an unmanned environment and arrange the maintenance timely to avoid the service life of the linear transmission devices being shortened due to insufficient lubrication has become the goal of relevant industries. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of the present disclosure, a linear transmission device with capability of real-time monitoring of an amount of a lubricant includes a long shaft, a moving part, a lubricating device and a detecting module. The moving part is movably disposed on the long shaft along an axial direction of the long shaft. The lubricating device includes a shell and an oil containing unit. The shell is fixed on one end of the moving part and formed with a first accommodating space. The oil containing unit is disposed in the first accommodating space and configured to provide the lubricant to an outer surface of the long shaft. The detecting module includes a temperature sensing unit and a control unit. The temperature sensing unit is disposed on the shell and adjacent to the oil containing unit. The temperature sensing unit is configured to detect a current temperature of the oil containing unit. The control unit is connected with the temperature sensing unit. The control unit is configured to: receive the current temperature; calculate a remaining amount of the lubricant of the oil containing unit based on the current temperature and an oil releasing model; and output the remaining amount. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a three-dimensional diagram showing a linear transmission device according to one embodiment of the present disclosure. 
         FIG.  2    is an exploded diagram showing the linear transmission device of  FIG.  1   . 
         FIG.  3    is a partial cross-sectional view of the linear transmission device of  FIG.  1   . 
         FIG.  4    is an exploded diagram showing a lubricating device of  FIG.  1   . 
         FIG.  5    is a functional block diagram of a detecting module and a signal receiving unit according to one embodiment of the present disclosure. 
         FIG.  6    is a flow chart of a control unit monitoring an amount of a lubricant. 
         FIG.  7    is a flow chart of establishing an oil releasing model according to one embodiment of the present disclosure. 
         FIG.  8    is a flow chart of calculating an oil releasing rate per unit time of an oil containing unit corresponding to each of reference temperatures according to one embodiment of the present disclosure. 
         FIG.  9    is a diagram showing a relationship between the reference temperatures and the oil releasing rates. 
         FIG.  10    is an exploded diagram showing a lubricating device according to another embodiment of the present disclosure. 
         FIG.  11    is a three-dimensional diagram showing a linear transmission device according to another embodiment of the present disclosure. 
         FIG.  12    is an exploded diagram showing a lubricating device of  FIG.  11   . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of the embodiments, reference is made to the accompanying drawings which form a part thereof, and in which is shown by way of illustration specific embodiments in which the disclosure may be practiced. In this regard, directional terminology, such as top, bottom, left, right, front or back, is used with reference to the orientation of the Figure (s) being described. The components of the present disclosure can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. In addition, identical components or similar numeral references are used for identical components or similar components in the following embodiments. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
     Please refer to  FIG.  1    to  FIG.  5   .  FIG.  1    is a three-dimensional diagram showing a linear transmission device  10  according to one embodiment of the present disclosure.  FIG.  2    is an exploded diagram showing the linear transmission device  10  of  FIG.  1   .  FIG.  3    is a partial cross-sectional view of the linear transmission device  10  of  FIG.  1   .  FIG.  4    is an exploded diagram showing a lubricating device  130  of  FIG.  1   .  FIG.  5    is a functional block diagram of a detecting module  200  and a signal receiving unit  230  according to one embodiment of the present disclosure. The linear transmission device  10  includes a long shaft  110 , a moving part  120 , two lubricating devices  130  and a detecting module  200 . The linear transmission device  10  can selectively include a plurality of balls  160 , two circulating elements  170  and an electronic device  240 . 
     As shown in  FIG.  1    and  FIG.  2   , in the embodiment, the linear transmission device  10  is a ball screw, the long shaft  110  is a screw shaft, and the moving part  120  is a nut. An outer surface  111  of the long shaft  110  is formed with a plurality of outer thread grooves  112 . The moving part  120  is movably disposed on the long shaft  110  along an axial direction A of the long shaft  110 . An inner surface  121  of the moving part  120  is formed with a plurality of inner thread grooves  122 . The inner thread grooves  122  and the outer thread grooves  112  together form a load path to cooperate with the circulating elements  170 , such that the balls  160  can circulate in the load path and the circulating elements  170 . In other embodiment, the linear transmission device  10  can be, but is not limited to, a linear guideway or a ball spline. For example, when the linear transmission device  10  is the linear guideway, the long shaft  110  can be a sliding rail, and the moving part  120  can be a sliding block; when the linear transmission device  10  is the ball spline, the long shaft  110  can be a spline shaft, and the moving part  120  can be a spline nut. 
     As shown in  FIG.  3    and  FIG.  4   , the two lubricating devices  130  are fixedly disposed on two ends of the moving part  120 , respectively. Each of the lubricating devices  130  includes a shell  140  and an oil containing unit  150 . The shell  140  is fixed on one end of the moving part  120  and formed with a first accommodating space  143 . In the embodiment, the shell  140  includes a first shell  141  and a second shell  142 . The first shell  141  is formed with a first through hole  145  and an annular groove  146 . The first through hole  145  is inserted by the long shaft  110 . The annular groove  146  surrounds the first through hole  145 . The second shell  142  is assembled with the first shell  141 , such that the first accommodating space  143  is formed between the first shell  141  and the second shell  142 . The second shell  142  is formed with a second through hole  147  to be inserted by the long shaft  110 . 
     The oil containing unit  150  is disposed in the first accommodating space  143  and configured to provide the lubricant to the outer surface  111  of the long shaft  110 . In the embodiment, the oil containing unit  150  includes a solid lubricating material  151  and a guiding part  152 . The solid lubricating material  151  can include the lubricant and a carrier (such as polymer, synthetic resin, teflon or paraffin wax) to carry the lubricant. The guiding part  152  can be made of a material capable of absorbing the lubricant, such as sponge or wool felt. The solid lubricating material  151  is disposed in the annular groove  146 . The guiding part  152  is adjacent to the solid lubricating material  151  and closes the annular groove  146 . The lubricant released from the solid lubricating material  151  is transferred to the outer surface  111  of the long shaft  110  through the guiding part  152 . In the embodiment, the guiding part  152  also functions as an oil seal. 
     As shown in  FIG.  3   ,  FIG.  4    and  FIG.  5   , the detecting module  200  includes temperature sensing units  210  and a control unit  220 . Each of the temperature sensing units  210  is disposed on the shell  140  and adjacent to the oil containing unit  150 . The temperature sensing unit  210  is configured to detect a current temperature of the oil containing unit  150 . In the embodiment, a number of the temperature sensing units  210  is two, which is corresponding to a number of the lubricating devices  130 . The two temperature sensing units  210  are disposed in the shells  140  of the two lubricating devices  130 , respectively. The two temperature sensing units  210  are configured to detect the current temperatures of the two oil containing units  150 . That is, the linear transmission device  10  according to the present disclosure can separately monitor remaining amounts of the lubricant of multiple oil containing units  150 . The aforementioned “each of the temperature sensing units  210  is disposed on the shell  140  and adjacent to the oil containing unit  150 ” refers that each of the temperature sensing units  210  can be disposed on an outer surface the shell  140 , on an inner surface the shell  140  or in the first accommodating space  143  (that is, the temperature sensing unit  210  can be fixed on other elements instead of being fixed on the shell  140 , and the position where the temperature sensing unit  210  disposed is close to the oil containing unit  150 . When the position where the temperature sensing unit  210  disposed is closer to the oil containing unit  150 , the temperature detected by the temperature sensing unit  210  is closer to the actual temperature of the oil containing unit  150 . In the embodiment, each of the temperature sensing units  210  is disposed in the first accommodating space  143  and is disposed on the solid lubricating material  151 . Specifically, the temperature sensing unit  210  is disposed between the groove bottom  146   a  of the annular groove  146  and the solid lubricating material  151 , one surface of the temperature sensing unit  210  faces the groove bottom  146   a , and another surface of the temperature sensing unit  210  faces the solid lubricating material  151 . 
     As shown in  FIG.  5   , the control unit  220  is connected with the temperature sensing unit  210 . The control unit  220  can be connected with the temperature sensing unit  210  in a wired manner or wireless manner. The control unit  220  has capability of calculation. The control unit  220  can be, but is not limited to, a central processing unit (CPU) or an electronic device including a CPU, such as a computer or a mobile phone. Please also refer to  FIG.  1   . In the embodiment, the linear transmission device  10  includes an electronic device  240 . The electronic device  240  is disposed on the shell  140  of the lubricating device  130 . The control unit  220  is disposed inside the electronic device  240 . The electronic device  240  can further include a signal receiving unit  230 . In the embodiment, the signal receiving unit  230  is a display screen. The signal receiving unit  230  is connected with the control unit  220 . The signal receiving unit  230  can be connected with the control unit  220  in a wired manner or wireless manner. The signal receiving unit  230  is configured to receive and display the signal transmitted from the control unit  220 , such as the remaining amount of the lubricant or a warning signal. As such, the worker located around the linear transmission device  10  can monitor the amount of the lubricant of the linear transmission device  10  by the signal displayed by the signal receiving unit  230 . In other embodiment, the control unit  220  and the signal receiving unit  230  can be remote devices. The control unit  220  and the signal receiving unit  230  can be integrated in a same electronic device, can be disposed in different electronic devices, or can be independent electronic devices. For example, the linear transmission device  10  can be disposed in a machine located in a factory, the control unit  220  and the signal receiving unit  230  can be integrated in a computer located in the office, such that the worker can remotely monitor the linear transmission device  10  in the office. Alternatively, the control unit  220  can be a computer located in the office, and the signal receiving unit  230  can be a mobile phone of the worker, such that the worker can remotely monitor the amount of the lubricant of the linear transmission device  10  at different locations. 
       FIG.  6    is a flow chart of the control unit  220  monitoring the amount of the lubricant. The control unit  220  is configured to perform Step  310  to Step  340 , and selectively perform Step  350  and Step  360 . In Step  310 , an oil releasing model is established. In Step  320 , a current temperature is received. In Step  330 , a remaining amount of the lubricant of the oil containing unit  150  is calculated based on the current temperature and the oil releasing model. In Step  340 , the remaining amount is output. In Step  350 , whether the remaining amount is less than a threshold is determined. In Step  360 , a warning signal is sent. 
     Regarding Step  310 , since the solid lubricating material  151  has different oil releasing rates at different temperatures, through Step  310 , the temperatures and the oil releasing rates of the solid lubricating material  151  can be collected to establish the oil releasing model thereof. In addition, the solid lubricating materials  151  of different material/model/viscosity have different oil releasing rates at the same temperature. Through Step  310 , the oil releasing models can be established for the solid lubricating materials  151  of different material/model/viscosity. The following will explain how to collect the temperatures and the oil releasing rates of a same solid lubricating material  151  to establish the oil releasing model thereof. 
       FIG.  7    is a flow chart of establishing an oil releasing model according to one embodiment of the present disclosure, which includes Step  311  and Step  312 , and can selectively include Step  313 . In Step  311 , a plurality of reference temperatures are preset, wherein the plurality of reference temperatures are different from one another. In Step  312 , an oil releasing rate per unit time of the oil containing unit  150  corresponding to each of the reference temperatures is calculated, so as to obtain a plurality of oil releasing rates. In Step  313 , the plurality of reference temperatures and the plurality of oil releasing rates are fitted to obtain a fitting equation. 
     In Step  311 , the plurality of reference temperatures can be selected according to the operating temperature range of the linear transmission device  10  and the desired accuracy. For example, when the operating temperature range of the linear transmission device  10  is 30° C. to 70° C., the temperatures with 20° C. interval therebetween within the operating temperature range can be selected as the plurality of reference temperatures, i.e., the temperatures of 30° C., 50° C. and 70° C. can be selected as the plurality of reference temperatures. For another example, the temperatures with 10° C. interval therebetween within the operating temperature range can be selected as the plurality of reference temperatures, i.e., the temperatures of 30° C., 40° C., 50° C., 60° C. and 70° C. can be selected as the plurality of reference temperatures. When the temperature interval between the reference temperatures is smaller, the accuracy is higher. According to one embodiment, the temperature interval between the reference temperatures is 10° C. 
     Regarding Step  312 , please refer to  FIG.  8   , which is a flow chart of calculating the oil releasing rate per unit time of the oil containing unit  150  corresponding to each of the reference temperatures according to one embodiment of the present disclosure, and includes Step  316  to Step  318 . In Step  316 , a first weight of the oil containing unit  150  at each of the reference temperatures is measured. In Step  317 , a second weight of the oil containing unit at each of the reference temperatures after a predetermined time is measured. In Step  318 , the oil releasing rate per unit time of the oil containing unit  150  corresponding to each of the reference temperatures based on the first weight, the second weight and the predetermined time is calculated. For example, in Step  316 , the first weight of the oil containing unit  150  at 30° C. is Wi gram (g). In Step  317 , the second weight of the oil containing unit  150  at 30° C. after one hour (i.e., 60 minutes) is Wf g. In Step  318 , the oil releasing rate per minute (min) of the oil containing unit  150  corresponding to 30° C. is (Wf−Wi)/60, the unit of the oil releasing rate per minute is g/min. When the oil containing unit  150  includes the solid lubricating material  151  and the guiding part  152 , the lubricant is provided by the solid lubricating material  151 , and the guiding part  152  does not consume. Therefore, the oil releasing rate per unit time of the oil containing unit  150  corresponding to each of the reference temperatures can be regarded as the oil releasing rate per unit time of the solid lubricating material  151  corresponding to each of the reference temperatures. According to the foregoing calculation method, it can be seen that the “the oil releasing rate” in the present disclosure refers to the oil releasing rate per unit time, which can also be referred to as the oil releasing rate for the sake of conciseness. Through Step  312 , the oil releasing rate per unit time of the oil containing unit  150  corresponding to each of the reference temperatures can be obtained. That is, a database of the reference temperatures and the oil releasing rates of the oil containing unit  150  can be established. 
     In Step  313 , the data obtained in Step  312  is processed to obtain the fitting equation. The fitting equation can be obtained based on polynomial, least square method, regression analysis, etc. In addition, the fitting equation can be calculated by available calculation software such as Excel. 
     In other words, the oil releasing model according to the present disclosure can be the database of the reference temperatures and the oil releasing rates obtained in Step  312  or the fitting equation obtained by fitting the data of the database. The oil releasing model can be used as the basis for estimating the remaining amount of the lubricant of the oil containing unit  150 . 
     Refer back to  FIG.  6   . In Step  330 , the remaining amount of the lubricant can be calculated as follows. Assuming that the remaining amount of the lubricant is W 2 , the initial weight of the lubricant is W 1 , the oil releasing rate of the reference temperature t is R t , and the oil releasing time is T, the releasing amount M of the lubricant can be obtained by Formula (I), and the remaining amount of the lubricant W 2  can be obtained by Formula (II): 
         M=R   t   ×T   (I);
 
         W 2=( W 1− M )  (II);
 
     wherein the unit of each of W 1 , W 2  and M can be a weight unit such as gram (g), the unit of R t  can be weight unit/time unit such as g/min; the unit of T can be a time unit such as minute (min). 
     Hereinafter, Step  320  and Step  330  will be illustrated by practical examples. Please refer to Table 1, which is an oil releasing model of the linear transmission device  10  shown in  FIG.  1    to  FIG.  4    and is obtained by Step  311  and Step  312 , wherein the viscosity of the solid lubricating material  151  is 68 cst. Herein, the oil releasing model is a database of the reference temperatures and the oil releasing rates. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 reference 
                   
                   
                   
                   
                   
               
               
                 temperature (° C.) 
                 30 
                 40 
                 50 
                 60 
                 70 
               
               
                   
               
             
            
               
                 oil releasing 
                 1.1736 × 10 −4   
                 3.0141 × 10 −4   
                 7.2847 × 10 −4   
                 1.4115 × 10 −3   
                 2.2556 × 10 −3   
               
               
                 rate (g/min) 
               
               
                   
               
            
           
         
       
     
     Assume that the detection frequency in  FIG.  6    is 1 time/min. That is, the control unit  220  performs Step  320  once every minute. When the current temperature of Step  320  is 40° C., the oil releasing rate R 40  is 3.0141×10 −4  g/min according to Table 1. The time interval between two detections is regarded as the oil releasing time. Herein, the oil releasing time is 1 min. According to Formula (I) and Formula (II), the oil releasing amount M and the remaining amount W 2  of the lubricant are as follows: M=3.0141×10 −4  g/min×1 min, W2=W1−3.0141×10 −4  g/min×1 min. The initial weight of the lubricant at the most beginning can be measured in advance. For example, the weight of a brand new oil containing unit  150  can be firstly measured, and then the weight of the oil containing unit  150  which has released all the lubricant therein is measured. The difference between the two weights can be regarded as the initial weight of the lubricant at the most beginning (that is, the weight of the lubricant when the linear transmission device  10  operates for 0 minutes). The remaining amount of the lubricant after the linear transmission device  10  operated for 1 minute can be calculated by substituting the initial weight of the lubricant at the most beginning into W 1  of Formula (II). When performing the second detection (that is, at the beginning of the second minute after the linear transmission device  10  is operated), the remaining amount of the lubricant after the linear transmission device  10  operated for 1 minute is used as the initial weight of the lubricant in the second detection. Then the releasing amount and the remaining amount of the lubricant at the second minute can be calculated by Formula (I) and Formula (II). As such, the remaining amount of the lubricant after the linear transmission device  10  operated for 2 minutes can be calculated. The remaining amount of the lubricant of the linear transmission device  10  for every additional minute of operation can be calculated in a similar manner. 
     Assuming that the current temperature received by the control unit  220  lacks corresponding oil releasing rate in the database, the corresponding oil releasing rate can be calculated by interpolation or extrapolation. For example, when the current temperature of Step  320  is 42.5° C., the oil releasing rate R 42.5  at 42.5° C. can be calculated by interpolation, as shown in Formula (III): 
     
       
         
           
             
               
                 
                   
                     
                       50 
                       - 
                       40 
                     
                     
                       
                         7.2847 
                         × 
                         
                           10 
                           
                             - 
                             4 
                           
                         
                       
                       - 
                       
                         3.0141 
                         × 
                         
                           10 
                           
                             - 
                             4 
                           
                         
                       
                     
                   
                   = 
                   
                     
                       
                         42.5 
                         - 
                         40 
                       
                       
                         
                           R 
                           42.5 
                         
                         - 
                         
                           3.0141 
                           × 
                           
                             10 
                             
                               - 
                               4 
                             
                           
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   III 
                   ) 
                 
               
             
           
         
       
     
     For another example, when the current temperature of Step  320  is 74° C., the oil releasing rate R 74  at 74° C. can be calculated by extrapolation, as shown in Formula (IV): 
     
       
         
           
             
               
                 
                   
                     
                       70 
                       - 
                       60 
                     
                     
                       
                         2.2556 
                         × 
                         
                           10 
                           
                             - 
                             3 
                           
                         
                       
                       - 
                       
                         1.4115 
                         × 
                         
                           10 
                           
                             - 
                             3 
                           
                         
                       
                     
                   
                   = 
                   
                     
                       
                         74 
                         - 
                         70 
                       
                       
                         
                           R 
                           74 
                         
                         - 
                         
                           2.2556 
                           × 
                           
                             10 
                             
                               - 
                               3 
                             
                           
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   IV 
                   ) 
                 
               
             
           
         
       
     
     After the oil releasing rate is calculated, the remaining amount of lubricating oil can be calculated by Formula (I) and Formula (II). 
     Please refer to  FIG.  9   , which is a diagram showing a relationship between the reference temperatures and the oil releasing rates, which is obtained by plotting the data in Table 1. The curve in  FIG.  9    is determined to be approximate to a quadratic polynomial by observation, and the fitting equation of Formula (V) can be obtained according to Step  313 . First, assuming that y=ax 2 +bx+cy, the temperature of 30° C., 50° C. and 70° C. are substituted into x of the equation, respectively: 
     
       
         
           
             { 
             
               
                 
                   
                     
                       1.1736 
                       × 
                       
                         10 
                         
                           - 
                           4 
                         
                       
                     
                     = 
                     
                       
                         
                           30 
                           2 
                         
                         ⁢ 
                         a 
                       
                       + 
                       
                         30 
                         ⁢ 
                         b 
                       
                       + 
                       c 
                     
                   
                 
               
               
                 
                   
                     
                       7.2847 
                       × 
                       
                         10 
                         
                           - 
                           4 
                         
                       
                     
                     = 
                     
                       
                         
                           50 
                           2 
                         
                         ⁢ 
                         a 
                       
                       + 
                       
                         50 
                         ⁢ 
                         b 
                       
                       + 
                       c 
                     
                   
                 
               
               
                 
                   
                     
                       2.2556 
                       × 
                       
                         10 
                         
                           - 
                           3 
                         
                       
                     
                     = 
                     
                       
                         
                           70 
                           2 
                         
                         ⁢ 
                         a 
                       
                       + 
                       
                         70 
                         ⁢ 
                         b 
                       
                       + 
                       c 
                     
                   
                 
               
             
           
         
       
     
     The following fitting equation can be obtained by solving a, b and c: 
         y= 1.1451×10 −6   x   2 −6.1049×10 −5   x+ 9.1827×10 −4   (V).
 
     In Formula (V), y represents the oil releasing rate, and x represents temperature (the reference temperature/the current temperature). By substituting the current temperature of Step  320  into x of Formula (V), the oil releasing rate corresponding to the current temperature of Step  320  can be obtained. Afterward, the remaining amount of the lubricant can be obtained by Formula (I) and Formula (II) based on the oil releasing rate. According to one embodiment of the present disclosure, the oil releasing rate calculated by the fitting equation of Formula (V) is 1.502%, the actual oil releasing rate is 1.15%, and the difference therebetween is 0.352%, which shows that the present disclosure can accurately estimate the oil releasing rate. Accordingly, the remaining amount of the lubricant can be accurately estimated, and the amount of the lubricant of the linear transmission device  10  can be effectively monitored. 
     Refer back to  FIG.  6   . In Step  340 , the remaining amount is output. That is, the control unit  220  sends the remaining amount to the signal receiving unit  230 . In Step  350 , whether the remaining amount is less than the threshold is determined. The threshold is preset. For example, the threshold can be 0 grams or 10% of the initial weight of the lubricant at the most beginning. When the remaining amount is less than the threshold, it means that the lubricant is exhausted or is about to be exhausted. At this time, Step  360  is performed, wherein the control unit  220  sends the warning signal. The warning signal can be a sound signal and/or a light signal, In this case, the signal receiving unit  230  may be equipped with a sound module and/or a light module to emit the sound signal and/or the light signal. When the remaining amount is greater than or equal to the threshold, it means that the lubricant is sufficient. At this time, Step  320  is performed to continue the detection. Steps  350  and  360  are selective steps. In other embodiments, when Steps  350  and  360  are not included, Step  320  is performed after Step  340  is performed. In addition, the oil releasing model can be established in advance. Once the oil releasing model is established, the subsequent detection can be started directly from Step  320 . 
     According to the above description, the linear transmission device  10  according to the present disclosure has capability of real-time monitoring of the amount of the lubricant. With the oil releasing model and detecting the current temperature of the oil containing unit  150 , the remaining amount of the lubricant can be estimated. Therefore, it can know that the lubricant is exhausted or about to be exhausted in real time. 
     Refer to  FIG.  10   , which is an exploded diagram showing a lubricating device  130 ′ according to another embodiment of the present disclosure. The first shell  141 ′ is formed with a first through hole  145 ′ and an annular groove  146 ′. The difference between the lubricating device  130 ′ and the lubricating device  130  is that an inner annular wall  148 ′ is formed with a second accommodating space  144 ′. The second accommodating space  144 ′ is communicated with a first accommodating space  143 ′. The temperature sensing unit  210  is disposed in the second accommodating space  144 ′. One surface of the temperature sensing unit  210  faces the inner annular wall  148 ′, and another surface of the temperature sensing unit  210  faces the solid lubricating material  151 . A shape of the second accommodating space  144 ′ can be arranged to cooperate with a shape of the temperature sensing unit  210 , such that the temperature sensing unit  210  can be embedded in the second accommodating space  144 ′. As such, the effect for positioning the temperature sensing unit  210  can be improved. For other details of lubricating device  130 ′, references can be made to the relevant description of the lubricating device  130 . 
     Refer to  FIG.  11    and  FIG.  12   .  FIG.  11    is a three-dimensional diagram showing a linear transmission device  40  according to another embodiment of the present disclosure.  FIG.  12    is an exploded diagram showing a lubricating device  430  of  FIG.  11   . The linear transmission device  40  includes a long shaft  410 , a moving part  420 , two lubricating devices  430  and a detecting module (not labelled). The linear transmission device  40  can selectively include an electronic device  540 . In the embodiment, the linear transmission device  40  is a linear guideway, the long shaft  410  is a sliding rail, and the moving part  420  is a sliding block. The moving part  420  is movably disposed on the long shaft  410  along an axial direction A of the long shaft  410 . 
     The two lubricating devices  430  are fixedly disposed on two ends of the moving part  420 , respectively. Each of the lubricating devices  430  includes a shell  440  and two oil containing units  450 . The shell  440  is fixed on one end of the moving part  420 . In the embodiment, the shell  440  includes a first shell  441  and a second shell  442 . The first shell  441  is an end cap. The second shell  442  is an oil scraper. The first shell  441  is formed with a first groove  445  and two first accommodating spaces  443 . The first groove  445  is inserted by the long shaft  410 . The two first accommodating spaces  443  are formed on two sides of the first groove  445  and are communicated with the first groove  445 . The second shell  442  is assembled with the first shell  441 . The second shell  442  is formed with a second groove  447  to be inserted by the long shaft  410 . 
     The oil containing unit  450  is configured to provide the lubricant to an outer surface  411  of the long shaft  410 . Each of the oil containing units  450  includes a solid lubricating material  451  and a guiding part  452 . The oil containing unit  450  is disposed in the first accommodating space  443 . The guiding part  452  is adjacent to the solid lubricating material  451 . The guiding part  452  protrudes from the first accommodating space  443  to the first groove  445 . A protruding length of the guiding part  452  is corresponding to a concave depth of the rail groove  412 , such that the lubricant released from the solid lubricating material  451  can be transferred to the outer surface  411  of the long shaft  410  through the guiding part  452 . 
     The detecting module includes temperature sensing units  510  and a control unit (not shown). Each of the temperature sensing units  510  is disposed on the shell  440  and adjacent to the one of the oil containing units  450 . In the embodiment, the number of the temperature sensing units  510  is four. Each of the lubricating devices  430  includes two temperature sensing units  510 . The two temperature sensing units  510  are disposed in the two first accommodating spaces  443  of the first shell  441 , respectively. The two temperature sensing units  510  are configured to detect the current temperatures of the two oil containing units  450 , respectively. The control unit is disposed inside the electronic device  540 . The electronic device  540  can further include a signal receiving unit  530 . In the embodiment, the signal receiving unit  530  is a display screen. 
     For other details of the linear transmission device  40 , references can be made to the relevant description of the linear transmission device  10 . 
     Comparing to prior art, the linear transmission device of the present disclosure is capable of estimating the remaining amount of the lubricant by temperature. It can know that the lubricant is exhausted or about to be exhausted in real time. Therefore, maintenance can be arranged timely, which is beneficial to prolonging the service life of the linear transmission device, and is beneficial to the application of unmanned factories. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.