Abstract:
A method for sensing depth of an object in three-dimensional space a Time-Of-Flight Sensing procedure and a Proximity-Sensing procedure are respectively operated in the same one period of time. The obtained information of the two procedures are manipulated to acquire the depth information of the measured object. With the result of the Time-Of-Flight Sensing procedure having high accuracy and the result of the Proximity-Sensing procedure having high resolution, the acquired depth information of the measured object is more precise.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application filed on Sep. 10, 2015 and having application Ser. No. 62/216,368, the entire contents of which are hereby incorporated herein by reference 
         [0002]    This application is based upon and claims priority under 35 U.S.C. 119 from Taiwan Patent Application No. 105103633 filed on Feb. 3, 2016, which is hereby specifically incorporated herein by this reference thereto. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to an optical sensing device, especially to a non-contact optical sensing device and method for sensing depth of an object in three-dimensional space. 
         [0005]    2. Description of the Prior Arts 
         [0006]    With the progress of the technology, electronic products change with each passing day. The ways to input data or command into the electronic products also advance. From the traditional physical keyboard as an input way, it develops to input with a virtual keyboard in touch panel. Recently, a non-contact way to input is also developed. The user does not need to touch the electronic device. The electronic device detects and identifies the user&#39;s gesture performing in the air through a non-contact sensor to execute a corresponding command. Especially to an apparatus that has an augmented reality (AR) function, using non-contact input is more intuitive and more convenient. Conventional non-contact sense mainly include two different ways. One way is to use proximity-sensing (PS) and another way is to use time-of-flight (TOF) sensing. 
         [0007]    The PS procedure utilizes the optical elements to emit light on the objects to generate reflected light and utilizes the energies of the reflected light to determine the depth of the objects. However, since the objects with different colors absorb the energies of light differently, the different objects at the same depth may be determined as locating at different depths. For example, when the user has metal ornaments worn on the fingers, the depths of the fingers and the metal ornaments are determined as locating at different depths since the meal ornaments and the fingers absorb energies of light differently. Therefore, using the PS procedure easily results in the misjudgment of the depths of the objects. 
         [0008]    The TOF sensing procedure utilizes the optical elements to emit light on the objects to generate reflected light and utilizes the time difference between the emitting time of the light and the receiving time of the reflected light to determine the depths of the objects. Since the velocity of light is not influenced by the absorbed energies of the objects, the depth determined by the TOF sensing procedure is more accurate than the depth determined by the PS procedure. 
         [0009]    However, the reliability of the determined depth of the TOF sensing procedure has a larger tolerance scope than the reliability of the determined depth of the PS procedure according to the following formulas. 
         [0010]    The TOF sensing procedure calculates the depth based on the data measured at different phases. The formula to calculate the tolerance scope δd of the depth d of the object is shown as following: 
         [0000]    
       
         
           
             d 
             = 
             
               
                 c 
                  
                 
                     
                 
                  
                 δ 
                  
                 
                     
                 
                  
                 T 
               
               = 
               
                 
                   
                     c 
                     ω 
                   
                    
                   φ 
                 
                 = 
                 
                   
                     
                       c 
                       ω 
                     
                      
                     
                       tan 
                       
                         - 
                         1 
                       
                     
                      
                     
                       
                         Q 
                         0 
                       
                       
                         Q 
                         90 
                       
                     
                   
                   ≈ 
                   
                     
                       c 
                       ω 
                     
                      
                     
                       
                         Q 
                         0 
                       
                       
                         Q 
                         90 
                       
                     
                   
                 
               
             
           
         
       
       
         
           
             
               δ 
                
               
                   
               
                
               d 
             
             = 
             
               
                 c 
                 ω 
               
                
               
                 ( 
                 
                   
                     
                       δ 
                        
                       
                           
                       
                        
                       
                         Q 
                         0 
                       
                     
                     
                       Q 
                       90 
                     
                   
                   - 
                   
                     
                       
                         Q 
                         0 
                       
                        
                       δ 
                        
                       
                           
                       
                        
                       
                         Q 
                         90 
                       
                     
                     
                       Q 
                       90 
                       2 
                     
                   
                 
                 ) 
               
             
           
         
       
       
         
           
             
               
                 δ 
                  
                 
                     
                 
                  
                 d 
               
               d 
             
             = 
             
               
                 
                   
                     Q 
                     90 
                   
                   
                     Q 
                     0 
                   
                 
                  
                 
                   ( 
                   
                     
                       
                         δ 
                          
                         
                             
                         
                          
                         
                           Q 
                           0 
                         
                       
                       
                         Q 
                         90 
                       
                     
                     - 
                     
                       
                         
                           Q 
                           0 
                         
                          
                         δ 
                          
                         
                             
                         
                          
                         
                           Q 
                           90 
                         
                       
                       
                         Q 
                         90 
                         2 
                       
                     
                   
                   ) 
                 
               
               = 
               
                 
                   
                     δ 
                      
                     
                         
                     
                      
                     
                       Q 
                       0 
                     
                   
                   
                     Q 
                     90 
                   
                 
                 - 
                 
                   
                     δ 
                      
                     
                         
                     
                      
                     
                       Q 
                       90 
                     
                   
                   
                     Q 
                     90 
                   
                 
               
             
           
         
       
       
         
           
             
               σ 
                
               
                 ( 
                 
                   
                     δ 
                      
                     
                         
                     
                      
                     d 
                   
                   d 
                 
                 ) 
               
             
             = 
             
               
                 
                   
                     σ 
                     2 
                   
                    
                   
                     ( 
                     
                       
                         σ 
                          
                         
                             
                         
                          
                         
                           Q 
                           0 
                         
                       
                       
                         Q 
                         0 
                       
                     
                     ) 
                   
                 
                 + 
                 
                   
                     σ 
                     2 
                   
                    
                   
                     ( 
                     
                       
                         σ 
                          
                         
                             
                         
                          
                         
                           Q 
                           90 
                         
                       
                       
                         Q 
                         90 
                       
                     
                     ) 
                   
                 
               
             
           
         
       
     
         [0011]    The Poisson distribution of the TOF sensing procedure is: 
         [0000]    
       
         
           
             
               
                 σ 
                  
                 
                   ( 
                   
                     Q 
                     
                       δ 
                        
                       
                           
                       
                        
                       Q 
                     
                   
                   ) 
                 
               
               -&gt; 
               
                 
                   N 
                 
                  
                 
                     
                 
                  
                 where 
                  
                 
                     
                 
                  
                 N 
               
             
             = 
             
               Q 
               q 
             
           
         
       
     
         [0012]    The unreliability of the depth is: 
         [0000]    
       
         
           
             
               σ 
                
               
                 ( 
                 
                   
                     δ 
                      
                     
                         
                     
                      
                     d 
                   
                   d 
                 
                 ) 
               
             
             = 
             
               
                 
                   
                     1 
                     
                       N 
                       0 
                     
                   
                   + 
                   
                     1 
                     
                       N 
                       90 
                     
                   
                 
               
               = 
               
                 
                   1 
                   
                     
                       ( 
                       
                         
                           SNR 
                           0 
                         
                         SNR 
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         
                           SNR 
                           90 
                         
                         SNR 
                       
                       ) 
                     
                   
                 
                  
                 
                   1 
                   SNR 
                 
               
             
           
         
       
       
         
           
             
               1 
               
                 
                   ( 
                   
                     
                       SNR 
                       0 
                     
                     SNR 
                   
                   ) 
                 
                  
                 
                   ( 
                   
                     
                       SNR 
                       90 
                     
                     SNR 
                   
                   ) 
                 
               
             
             &gt; 
             1 
           
         
       
     
         [0013]    The “N 0 ” and “N 99 ” represents the amount of the photons at the 0 degrees phase and 90 degrees phase. Therefore, the formula represents the nonlinear relationship between the unreliability of the depth and the amount of the photons. 
         [0014]    On the other hand, the PS procedure calculates the depth of the object based on the intensity of the reflected light. The formula of the PS procedure is as following: 
         [0000]    
       
         
           
             Q 
             = 
             
               K 
               
                 d 
                 2 
               
             
           
         
       
       
         
           
             
               δ 
                
               
                   
               
                
               Q 
             
             = 
             
               
                 K 
                  
                 
                   ( 
                   
                     
                       - 
                       2 
                     
                      
                     
                       1 
                       
                         d 
                         3 
                       
                     
                   
                   ) 
                 
               
                
               δ 
                
               
                   
               
                
               d 
             
           
         
       
       
         
           
             
               
                 
                   δ 
                    
                   
                       
                   
                    
                   Q 
                 
                 Q 
               
               = 
               
                 
                   - 
                   2 
                 
                  
                 
                   
                     δ 
                      
                     
                         
                     
                      
                     d 
                   
                   d 
                 
               
             
              
             
                 
             
           
         
       
       
         
           
             
               
                 δ 
                  
                 
                     
                 
                  
                 d 
               
               d 
             
             = 
             
               
                 - 
                 
                   1 
                   2 
                 
               
                
               
                 
                   δ 
                    
                   
                       
                   
                    
                   Q 
                 
                 Q 
               
             
           
         
       
       
         
           
             
               σ 
                
               
                 ( 
                 
                   
                     δ 
                      
                     
                         
                     
                      
                     d 
                   
                   d 
                 
                 ) 
               
             
             = 
             
               
                 - 
                 
                   1 
                   2 
                 
               
                
               
                 σ 
                  
                 
                   ( 
                   
                     
                       δ 
                        
                       
                           
                       
                        
                       Q 
                     
                     Q 
                   
                   ) 
                 
               
             
           
         
       
     
         [0015]    The Poisson distribution of the TOF sensing procedure is: 
         [0000]    
       
         
           
             
               
                 σ 
                  
                 
                   ( 
                   
                     
                       δ 
                        
                       
                           
                       
                        
                       Q 
                     
                     
                       
                           
                       
                        
                       Q 
                     
                   
                   ) 
                 
               
               -&gt; 
               
                 
                   1 
                   
                     N 
                   
                 
                  
                 
                     
                 
                  
                 where 
                  
                 
                     
                 
                  
                 N 
               
             
             = 
             
               Q 
               q 
             
           
         
       
     
         [0016]    The unreliability of the depth is: 
         [0000]    
       
         
           
             
               σ 
                
               
                 ( 
                 
                   
                     δ 
                      
                     
                         
                     
                      
                     d 
                   
                   d 
                 
                 ) 
               
             
             = 
             
               
                 
                   - 
                   
                     1 
                     2 
                   
                 
                  
                 
                   
                     1 
                     N 
                   
                 
               
               = 
               
                 - 
                 
                   1 
                   
                     2 
                      
                     SNR 
                   
                 
               
             
           
         
       
     
         [0017]    The formula represents the linear relationship between the unreliability of the depth and the amount of the photons. Therefore, the unreliability of the depth of the PS procedure is smaller than the unreliability of the depth of the TOF sensing procedure. 
         [0018]    Since the signal-to-noise ration (SNR) is inversely proportional to the unreliability, the SNR of the TOF sensing procedure is less than the SNR of the PS procedure. It means that the tolerance scope of the depth measured by the TOF sensing procedure is larger than the tolerance scope of the depth measured by the PS procedure. For example, if the tolerance scope of the depth measured by the TOF sensing procedure is 0.02, the tolerance scope of the depth measured by the PS procedure may be 0.005. Therefore, the resolution of the PS procedure is higher than the resolution of the TOF sensing procedure. 
       SUMMARY OF THE INVENTION 
       [0019]    To overcome the aforementioned shortcomings of the two conventional ways, the present invention provides a non-contact optical sensing device and method for sensing depth of an object in three-dimensional space to mitigate or obviate the aforementioned problems. 
         [0020]    To achieve the aforementioned purpose, a method for sensing depth of an object in three-dimensional space, in one periodic time, comprising steps of: 
         [0021]    a. emitting light by a first emitting unit to the object to generate a first reflected light, and obtaining a first data based on a time difference between an emitting time of the first emitting unit to emit the light and a receiving time of the first reflected light; 
         [0022]    b. emitting light by a second emitting unit to the object to generate a second reflected light, and obtaining a second data based on an intensity of the second reflected light; and 
         [0023]    c. determining the depth of the object by calculating the first data and the second data. 
         [0024]    In addition, a non-contact optical sensing device of the present invention comprises: 
         [0025]    a first emitting unit adapted for emitting light to an object; 
         [0026]    a second emitting unit adapted for emitting light to the object; 
         [0027]    a photoelectric element adapted for receiving a reflected light from the object; 
         [0028]    a first switching element coupling to the photoelectric element; 
         [0029]    a second switching element coupling to the photoelectric element; 
         [0030]    a control unit electrically connecting to the first emitting unit, the second emitting unit, the photoelectric element, the first switching element and the second switching element, controlling the first and second switching elements to obtain an output of the photoelectric element, and alternatively switching on the first and second switching elements, wherein 
         [0031]    the control unit executes following steps in one periodic time: 
         [0032]    a. emitting light by the first emitting unit to the object to generate a first reflected light, and obtaining a first data based on a time difference between an emitting time of the first emitting unit to emit the light and a receiving time of the first reflected light received by the photoelectric element; 
         [0033]    b. emitting light by the second emitting unit to the object to generate a second reflected light, and obtaining a second data based on an intensity of the second reflected light; and 
         [0034]    c. determining the depth of the object by calculating the first data and the second data. 
         [0035]    The present invention has following advantages. By executing the TOF sensing procedure and the PS procedure in a periodic time, two depths of the object are obtained in two different procedures and are manipulated to obtain the depth of the object. Using the high accuracy of the TOF procedure to compensate the low accuracy of the PS procedure, and using the high resolution of the PS procedure to compensate the high accuracy of the TOF procedure. Therefore, the present invention determines the depth of the non-contact object in three-dimensional space more precisely. 
         [0036]    Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is an illustrative view of a non-contact optical sensing device in accordance with the present invention mounted in an electronic device; 
           [0038]      FIG. 2A  is a block diagram of the non-contact optical sensing device in  FIG. 1 ; 
           [0039]      FIG. 2B  is an operational block and signal diagram of the non-contact optical sensing device in  FIG. 1  when executing TOF sensing procedure; 
           [0040]      FIG. 2C  is an operational block and signal diagram of the non-contact optical sensing device in  FIG. 1  when executing PS procedure; 
           [0041]      FIG. 3  is a circuit diagram of a photoelectric element, a first switching element and a second switching element of the non-contact optical sensing device in  FIG. 1 ; 
           [0042]      FIG. 4A  is a flow chart of a first embodiment of a sensing method in accordance with the present invention; 
           [0043]      FIG. 4B  is a phase diagram of the sensing method in  FIG. 4A ; 
           [0044]      FIG. 5A  is a flow chart of a second embodiment of a sensing method in accordance with the present invention; 
           [0045]      FIG. 5B  is a phase diagram of the sensing method in  FIG. 5A ; 
           [0046]      FIG. 6  is a phase diagram of a third embodiment of a sensing method in accordance with the present invention; 
           [0047]      FIG. 7  is a phase diagram of a fourth embodiment of a sensing method in accordance with the present invention; 
           [0048]      FIG. 8  is a flow chart of a first embodiment of calculating the depth of the object in a sensing method in accordance with the present invention; 
           [0049]      FIG. 9  is a flow chart of a second embodiment of calculating the depth of the object in a sensing method in accordance with the present invention; 
           [0050]      FIG. 10  is an illustrative block diagram of one embodiment of the method in  FIG. 9 ; and 
           [0051]      FIG. 11  is an illustrative block diagram of another embodiment of the method in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0052]    With reference to  FIGS. 1 and 2A , a non-contact optical sensing device  10  in accordance with the present invention is implemented in an electronic device  20 . The non-contact optical sensing device  10  comprises at least one emitting unit  11 , a photoelectric element  12 , a first switching element  13 , a second switching element  14  and a control unit  15 . 
         [0053]    The emitting unit  11  emits light on an object to be measured and may comprise one or more than one light emitting diode (LED). In some embodiments as shown in  FIGS. 2B and 2C , the non-contact optical sensing device in accordance with the present invention comprises a first emitting unit  111  and a second emitting unit  112 . In one embodiment as shown in  FIG. 2A , the non-contact optical sensing device in accordance with the present invention comprises a single emitting unit  11 , i.e. the first emitting unit and the second emitting unit are the same emitting unit. 
         [0054]    The photoelectric element  12  receives the reflected light from the measured object. The reflected light is reflected from the light emitted on the measured object. The photoelectric element  12  may be a photogate or a photodiode. When the photoelectric element  12  receives and transforms the reflected light into corresponding photons to generate corresponding signals. With reference to  FIGS. 2A and 3 , the first switching element  13  and the second switching element  14  are coupled to the photoelectric element  12  to transmit the signal of the photoelectric element  12  to the control unit  15 . In one embodiment, the first switching element  13  comprises a first transfer gate TX 1 . The second switching element  14  comprises a second transfer gate TX 2 . The first switching element  13  is connected to a first electric charge storage relay point FD 1 . The second switching element  14  is connected to a second electric charge storage relay point FD 2 . 
         [0055]    The control unit  15  is connected electrically to the emitting unit  11 , the photoelectric element  12 , the first switching element  13  and the second switching element  14 . The control unit  15  controls the emitting unit  11  to be switched on and off, the electric potential of the photoelectric element  12 , and the first and second switching elements  13 ,  14  to be switched on and off, and obtains the signal from the photoelectric element  12  by switching the first and second switching elements  13 ,  14 . 
         [0056]    With reference to  FIGS. 2B, 2C, 4A and 5A , when the non-contact optical sensing device  10  is implemented, the control unit  15  executes a TOF sensing procedure and a PS procedure in a single periodic time. The control unit  15  sends control signals respectively to control the first emitting unit  111 , the second emitting unit  112 , the first switching element  13  and the second switching element  14 . The control unit  15  obtains the output of the photoelectric element  12  by controlling the first and second switching elements  13 ,  14 . The frequencies of the control signals for executing the TOF sensing procedure and the PS procedure are different. The TOF sensing procedure utilizes a time difference between the emitting time of the light emitted from the first emitting unit  11  and the receiving of the reflected light received by the photoelectric element  12  to obtain a first data of a depth of the measured object. The PS procedure utilizes the intensity of the reflected light received by the photoelectric element  12  to obtain the second data of the depth of the measured object, wherein the second emitting element  112  emits light to the measured object to generate the reflected light. The control unit  15  calculates and determines the depth of the measured object based on the first data and the second data. 
         [0057]    With reference to  FIGS. 2B, 4A and 4B , in one embodiment, the TOF sensing procedure is executed first and then the PS procedure is executed. The executing time of the TOF sensing procedure and the executing time of the PS procedure are the same. With reference to  FIGS. 2C, 5A and 5B , in another embodiment, the PS procedure is executed first and then the TOF sensing procedure is executed. 
         [0058]    With reference to  FIGS. 2B, 4B and 5B , when the TOF sensing procedure is executed, the control unit  15  controls the photoelectric element  12  to be switched on. The control unit  15  controls the first emitting unit  111  by a first control signal S 1 , controls the first switching element  13  by a second control signal S 2  and controls the second switching element  14  by a third control signal S 3 . The first control signal S 1  has a first emitting frequency. The second control signal S 2  and the third control signal S 3  have a first sampling frequency. The first emitting frequency is the same with the first sampling frequency. In one embodiment, when the first emitting element  111  is switched on, the first switching element  13  is turned on simultaneously while the second switching element  14  is delayed to be turned on. Specifically, a phase of the second control signal S 2  and a phase of the third control signal S 3  is different and the phase difference may be 90 degrees as shown in  FIGS. 4B and 5B , 180 degrees, 270 degrees and so on. Further, a phase of the first control signal S 1  and the phase of the second control signal S 2  may be the same, or the phase of the first control signal S  1  and the phase of the third control signal S 3  may be the same. In one embodiment, the second control signal S 2  is supplied to the first transfer gate TX 1 . The third control signal S 3  is supplied to the second transfer gate TX 2 . 
         [0059]    With reference to  FIGS. 2C, 4B and 5B , when the PS procedure is executed, the control unit  15  controls the photoelectric element  12  to be switched on. The control unit  15  controls the second emitting unit  112  by a fourth control signal S 4 , controls the first switching element  13  by a fifth control signal S 5  and controls the second switching element  14  by a sixth control signal S 6 . The fourth control signal S 4  has a second emitting frequency. The fifth control signal S 5  and the sixth control signal S 6  have a second sampling frequency. The second emitting frequency is the same with the second sampling frequency. However, the first sampling frequency of the TOF sensing procedure is larger than the second sampling frequency of the PS procedure. In one embodiment, when the second emitting element  112  is switched on, the first switching element  13  is turned on simultaneously while the second switching element  14  is delayed to be turned on. Specifically, a phase of the fifth control signal S 5  and a phase of the sixth control signal S 6  is different and the phase difference may be 90 degrees, 180 degrees as shown in  FIGS. 4B and 5B , 270 degrees and so on. Further, a phase of the fourth control signal S 4  and the phase of the fifth control signal S 5  may be the same, or the phase of the fourth control signal S 4  and the phase of the sixth control signal S 6  may be the same. In one embodiment, the fifth control signal S 5  is supplied to the first transfer gate TX 1 . The sixth control signal S 6  is supplied to the second transfer gate TX 2 . 
         [0060]    In addition, the time to execute the TOF sensing procedure may be longer than the time to execute the PS procedure as shown in  FIG. 6 . Otherwise, the time to execute the TOF sensing procedure may be shorter than the time to execute the PS procedure as shown in  FIG. 7 . 
         [0061]    Moreover, the calculation method of the control unit  15  to calculate and to determine the depth of the measured object based on the first data and the second data may comprises two different ways, but is not limited to the two ways. 
         [0062]    First method is shown in  FIG. 8 . The control unit  15  respectively multiplies the first data and the second data by two different weight parameters a, b to calculate and to obtain the depth of the measured object. In one embodiment, a is equal to b and is equal to 0.5, i.e. the first data and the second data multiply by 0.5 to obtain the depth of the measured object. 
         [0063]    With reference to  FIG. 9 , the control unit  15  obtains an initial depth of the measured object based on the first data obtained by executing the TOF sensing procedure. Then the PS procedure is executed to obtain the second data. The second data is used to correct and compensate the initial depth of the measured object so that a depth of the measured object is obtained. Therefore, using the first data with low resolution but with absolute depth data obtains the initial depth. Then using the second data with high resolution corrects the initial depth to obtain the depth of the measured object. In one embodiment, the sequence to execute the TOF sensing procedure and the PS procedure is changeable. In one embodiment as shown in  FIG. 10 , in a periodic time, an initial depth z 1  is obtained by executing one TOF sensing procedure. Two auxiliary depths z′ 11 , z′ 12  are obtained by executing two PS procedures. One of the auxiliary depths is subtracted from another one of the auxiliary depths to obtain a difference Δz′ 1 . 
         [0000]      Δ z′   1   =z′   12   −z′   11  
 
         [0064]    The difference A is used to correct and compensate the initial depth z 1 . Thus, the depth of the measured object is equal to the different Δz′ 1  plus the initial depth z 1 (z 1 +Δz′ 1 ). 
         [0065]    In another embodiment as shown in  FIG. 11 , in a periodic time, one TOF sending procedure and one PS procedure are executed and the obtained data of the two adjacent periodic times are compared to obtain the initial depth z 1  and auxiliary depths z′ 11 , z′ 12.  Then one of the auxiliary depths is subtracted from another one of the auxiliary depths to obtain the difference Δz′ 1 . 
         [0000]      Δ z′   1   =z′   12   −z′   11  
 
         [0066]    The difference Δz′ 1  is used to correct and compensate the initial depth z 1 . Thus, the depth of the measured object is equal to the different Δz′ 1  plus the initial depth z 1  (z 1 +Δz′ 1 ). 
         [0067]    Therefore, the non-contact optical sensing device in accordance with the present invention executes the TOF sensing procedure with high accuracy and the PS procedure with high resolution to obtain two different data of the depth of the measured object. After calculation, the depth of the measured object is obtained. Thus, the non-contact optical sensing device in accordance with the present invention has both advantages of high accuracy and high resolution to determine the depth of the object precisely. 
         [0068]    Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and features of the invention, the disclosure is illustrative only. Changes may be made in the details, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.