Abstract:
The force calculation system of the present invention is provided with: an air blowing unit for blowing air at a predetermined pressure; a flow passage for air blown from air blowing unit; a sensing unit for changing the ease of flow of air that flows through a flow passage by deforming when an external force is given; a storage unit for storing in advance the flow volume-force correspondence information showing the correspondence between the magnitude of the force received by the sensing unit and the flow volume at which air blown from air blowing unit flows through the flow passage; and a processing unit for calculating the magnitude of external force received by the sensing unit, on the basis of: the flow volume of air flowing through the flow passage as measured by a flow volume meter; and the flow volume-force correspondence information stored in the storage unit.

Description:
FIELD OF THE INVENTION 
     This invention relates to technology of a force calculation system, which is able to calculate the strength of force applied to a target area without an electrical device. 
     DESCRIPTION OF THE RELATED ART 
     Some of conventional methods of measuring force are widely used, for example, a strain gauge method using a variation of an electrical resistance (hereinafter electrical strain sensor), or a load cell method with a sensing unit equipped with a piezoelectric element. However, these methods cannot be used in strong electromagnetic environment such as a MRI (Magnetic Resonance Imaging) device, since these sensors must use electrical phenomena. In addition, there is a risk of a problem with the measurement accuracy decreasing due to interference with another electrical device. 
     Thus, a light fiber type strain gauge (hereinafter, light fiber type sensor) has already put into practical use (see non-patent documents No. 1 and 2). This technology has no problem to be caused by electrical phenomena as above, because it detects variations due to strain of a sensing unit, e.g., a wavelength, frequency, phase, and percolation of the light. 
     Non-patent documents 
     Non-patent document No. 1: J. Peirs, et al., “A micro optical force sensor for force feedback during minimally invasive robotic surgery”, Sensors and Actuators A 115 (2004), pp. 447-455. 
     Non-patent document No. 2: P. Polygerinos, et al., “A Fibre-Optic Catheter-Tip Force Sensor with MRI Compatibility: A Feasibility Study”, 31st Annual International Conference of the IEEE EMBS Minneapolis, Minn., USA, Sep. 2-6, 2009, pp. 1501-1504. 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, an optical switch acting as an optical source and a signal conditioner for signal processing are required for the above light fiber type sensor. Therefore the whole system is more expensive and larger than the system of the electrical strain sensor. 
     Thus, in view of the above-mentioned situation, problems to be solved by this invention is to provide an undersized and inexpensive force calculation system, which is able to calculate the strength of force applied to a target area without an electrical device. 
     Means for Solving the Problem 
     To solve the above problem, a force calculation system comprises an air blowing unit for blowing air at a predetermined pressure, a flow passage connected to the air blowing unit for blowing air, a sensing unit arranged in the end portion of the flow passage on the side opposite to the air blowing unit wherein the ease of flow of air is changed by deformation due to external force, a flowmeter measuring flow volume of air flowing through the flow passage, a memory unit for storing in advance information of correspondence relation between the strength of external force at the sensing unit and the flow volume of air flowing through the flow passage from the air blowing unit, and a processing unit for calculating the strength of the external force applied to the sensing unit based on the flow volume of air flowing through the flow passage as measured by the flowmeter and the information of the correspondence relation stored by the memory unit, wherein the sensing unit comprises an aperture tucking the flow passage down, the aperture is made of a member which makes a width of the aperture change as a function of the external force, the end portion of the flow passage on the side opposite to the air blowing unit is connected to the aperture of the member, and the flow volume of air flowing the tube is changed by a variation of the width of the aperture due to the external force applied to the sensing unit. 
     Effects of the Invention 
     According to the present invention, it is possible to provide an undersized and inexpensive force calculation system, which is able to calculate the strength of force applied to a target area without an electrical device. 
    
    
     
       BRIEF DESCRIPTION OF INVENTION 
         FIG. 1  shows a schematic diagram of an embodiment of the force calculation system. 
         FIGS. 2A and 2B  show a structure of the tucked tube type sensing unit.  FIG. 2A  shows the structure before the external force is applied to the sensing unit.  FIG. 2B  shows the structure after the external force has been applied to the sensing unit. 
         FIGS. 3A-3D  show a structure of the slit type sensing unit.  FIGS. 3A and 3B  show the structure before the external force is applied to the sensing unit.  FIGS. 3C and 3D  show the structure after the external force has been applied to the sensing unit. 
         FIGS. 4A and 4B  show relationship between the external force applied to the sensing unit and the flow volume of air flowing through the flow passage.  FIG. 4A  shows a sample of the relationship using the tucked tube type sensing unit.  FIG. 4B  shows a sample of the relationship using the slit type sensing unit. 
         FIGS. 5A and 5B  show dynamic characteristics between the external force applied to the sensing unit and the flow volume of air flowing through the flow passage.  FIG. 5A  shows a sample of the relationship using the tucked tube type sensing unit.  FIG. 5B  shows a sample of the relationship using the slit type sensing unit. 
         FIG. 6  shows flowchart of processing flows in the processing unit of the computing device. 
         FIGS. 7A and 7B  show structures of flow passages and the sensing unit in the case of having three flow passages.  FIG. 7A  shows a sample of the structure using the tucked tube type sensing unit.  FIG. 7B  shows a sample of the structure using the slit type sensing unit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A force calculation system according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, for example, this embodiment assumes that a force calculation system  100  is used when it is necessary to obtain the strength of force such as weft tension in suturing or elasticity from internal organs to a crow-bill due to using an endoscopic operation robot. 
     As shown in  FIG. 1 , a force calculation system comprises an air blowing unit  1 , a flow passage  2 , a flowmeter  3 , a sensing unit  4 , and a processing unit  5 . The air blowing unit  1  is a device for blowing out air at a predetermined pressure. For example, the air blowing unit  1  may be implemented by a combination of a compressor and a regulator valve. The flow passage  2  through which air flows from the air blowing unit  1  is connected to the air blowing unit  1 . For example, the flow passage  2  may be implemented by a plastic tube. 
     In addition, hereinafter one end of the flow passage  2  on the side of the sensing unit  4  is called “leading end”, the other end of the side of the air blowing unit  1  is called “base end.” 
     The flowmeter  3  is a device for measuring the flow volume of air flowing through the flow passage. For example, the flowmeter  3  may be implemented by a laminar flow type flowmeter, which comprises a laminar flow element and a sensor measuring a differential pressure between both ends. The sensing unit  4  is disposed at the end of the flow passage  2 , and is deformed by the external force. The sensing unit  4  changes the ease of flow of air flowing through the flow passage  2  by deforming when the external force is applied to the sensing unit  4 , to be discussed in detail below. 
     The computing device  5  is a computer device comprising a receiving unit  51 , a processing unit  52 , a memory unit  53 , an input unit  54 , and an output unit  55 . The receiving unit  51  is a device for receiving measurement data of the flow volume from the flowmeter  3 . For example, the computing device  5  may be implemented by an application specific integrated circuit. 
     The processing unit  52  is a device for processing a variety of operations. For example, the processing unit  52  may be implemented by a central processing unit (CPU). Based on the measurement data of the flow volume of air flowing through the flow passage  2  and flow-volume-force correspondence relation information  531  stored in the memory unit  53 , the processing unit  52  calculates the strength of external force applied to the sensing unit  4 , to be discussed in detail below. 
     The memory unit  53  is a device for storing information. For example, the memory unit  53  may be implemented by a memory device such as a RAM (random access memory), a ROM (read only memory), or a HDD (hard disk drive) etc. The memory unit  53  stores the flow-volume-force correspondence relation information  531  between the external force applied to the sensing unit  4  and the flow volume of air which is blown out the air blowing unit and flows through the flow passage  2 . 
     More specifically, the flow-volume-force correspondence relation information  531  denotes data information shown in graphs of  FIGS. 4A and 4B . 
     The input unit  54  is a device for a user of computing device  5  to input information. For example, the input unit  54  may be implemented by a keyboard or a mouse. 
     The output unit  55  is a device for outputting information. For example, the output unit  55  may be implemented by a device such as an external communication interface or a liquid crystal display (LCD) etc. 
     Next, the sensing unit  4  is explained. In this embodiment, for example, two types of sensing units may be explained. One is a tucked tube type, and the other is a slit type. 
     Firstly, the tucked tube type sensing unit  4   a  is explained. 
       FIG. 2A  shows the tucked tube type sensing unit  4   a  made of stainless steel, and the sensing unit  4   a  may be implemented using coil spring where the middle part of a cylindrical body is formed into a coiled shape. The aperture  41  of the sensing unit  4   a  tucks the middle portion  22  near the end portion  21 . 
     In addition, it is necessary that the flow passage  2  is elastically deformable tube. Furthermore, for example, the sensing unit  4   a  has a diameter of 5 mm and an axial length of about 20 mm. 
       FIG. 2B  shows an aperture  41  of which a width is changed when the external force is applied to the sensing unit  4  in an axial direction. Thus the flow volume of air flowing through the flow passage  2  is changed, since an effective section area in the middle portion  22  is changed by a variation of the width of an aperture  41 . Here the effective section area means section area in the direction vertical to air flow passing direction. In addition, the end portion  21  is pressured at the atmospheric pressure. 
     Secondly, the tucked tube type sensing unit  4   b  is explained. 
       FIG. 3A  shows the sensing unit  4   b  made of a cylindrical aluminum material. The sensing unit  4   b  has a slit  42  of which an opening width is changed when the external force is applied to the sensing unit  4  in an axial direction (a determined direction). In addition, a hole is bored in a part of a sidewall of the sensing unit  4   b  so that the end portion  21  of the flow passage  2  is put in the sensing unit  4   b . Thus the end portion  21  of the flow passage  2  is arranged at the slit  42 . 
     In addition, it is not necessary that the flow passage  2  is made of an elastically deformable material. Furthermore, for example, the sensing unit  4   b  has a diameter of 10 mm and an axial length of about 15 mm. 
     In this case, as shown in  FIG. 3B , a leading end  21  of the flow passage  2  and a facing plane  43  are placed from each other by a distance of dl, i.e., a width of a slit  42 . 
       FIG. 3C  shows the flow passage  2  through which the flow volume of air is changed, since a distance between a leading end  21  of the flow passage  2  and a facing plane  43  is changed by a variation of a width of a slit  42 , when the external force is applied to the sensing unit  4   a  (see  FIG. 3D ). 
     In addition, the longer distance between a leading end  21  of the flow passage  2  and a facing plane  43  there is, the more flow volume increases. 
     Next, experimental results regarding correspondence relation between external force and the flow volume are explained. 
       FIG. 4A  shows results of the experiment on the tucked tube type sensing unit  4   a . When air pressure at the air blowing unit  1  is 400 kPaG, i.e., 400 kPa higher than 1 atmosphere, the result shown by a curved line L 1  is obtained. In  FIG. 4A , the coordinates show force F[N] in a horizontal axis and the flow volume [L/min(nor)] of air flowing through the flow passage  2  Q in a vertical axis. 
     In view of this experiment, the significant change of the flow volume of air flowing through the flow passage  2  is obtained, if the external force is applied to the sensing unit  4   a.    
       FIG. 4B  shows results of the experiment on the slit type sensing unit  4   b . When air pressure at the air blowing unit  1  is 50 kPaG, the result shown by a curved line L 2  is obtained. Here the coordinates show force F[N] in a horizontal axis and the flow volume [L/min(nor)] of air flowing through the flow passage  2  Q in a vertical axis. 
     In view of this experiment, the significant change of the flow volume of air flowing through the flow passage  2  is obtained, if the external force is applied to the sensing unit  4   b.    
     Next, experimental results regarding dynamic characteristics, i.e., temporal response performance of the flow volume variation to the external force are explained. 
       FIG. 5A  shows results of the experiment on the tucked tube type sensing unit  4   a . When the external force of about 20-25 N is several times applied to the sensing unit  4   a  by hands, the results shown by curved lines L 3  and L 4  are obtained. In  FIG. 5A , the coordinates show a time in a horizontal axis and the force F and the flow volume of air flowing through the flow passage  2  Q in a vertical axis. 
     In view of this experiment, the temporal change in the flow volume of air flowing through the flow passage  2  follows the temporal change of the external force applied to the sensing unit  4   a.    
       FIG. 5B  shows results of the experiment on the slit type sensing unit  4   b . When the external force of about 15-20 N is several times applied to the sensing unit  4   a  by hands, the results shown by curved lines L 5  and L 6  are obtained. In  FIG. 5B , the coordinates show a time in a horizontal axis and the Force F and the flow volume of air flowing through the flow passage  2  Q in a vertical axis. 
     In view of this experiment, the temporal change in the flow volume of air flowing through the flow passage  2  follows the temporal change of the external force applied to the sensing unit  4   b.    
     To evaluate dynamic characteristics of the sensing units  4   a  and  4   b , these experiments achieved adequate response performance enough to apply to tasks with operation frequency less than 2-3 Hz such as a surgical operation. 
     Next, it is explained how computing device  5  processes operations using the force calculation system  100 . 
     Firstly, the receiving unit  51  in the computing device  5  measures the flow volume of air flowing through the flow passage  2  (STEP  51 ). 
     More specifically, the receiving unit  51  receives measurement data of the flow volume of air flowing through the flow passage  2  from the flowmeter  3 . Based on these measurement data, the processing unit  52  understands (measures) the flow volume of air flowing through the flow passage  2   
     Secondly, the processing unit  52  refers to the flow-volume-force correspondence relation information  531  stored in the memory unit  53  (STEP  3 ). Based on the flow-volume-force correspondence relation information  531  and the flow volume of air flowing through the flow passage  2  measured in STEP  51 , the processing unit  52  calculates the strength of external force applied to the sensing unit  4 . 
     In addition, when the force calculation system  100  is applied to a surgical robot, for example, feedback control in which a remote-operating medical doctor automatically obtains the force calculated by the STEP S 3  may be executed. 
     Next, a processing unit  52  determines whether termination requirements are satisfied or not, wherein if this decision is “YES,” then the process terminates, and wherein if this decision is “NO,” then the process returns STEP  51 . 
     In addition, termination requirements may be requirements not only satisfied by manual operations such as input operations but also satisfied by auto operations in which it is executed when there is no external force applied to the sensing unit  4  during a predetermined time. 
     According to the above embodiment for the force calculation system  100 , since the sensing unit  4  changes the ease of flow of air flowing through the flow passage  2  by deforming when the external force is applied to the sensing unit  4 . The external force applied to the sensing unit  4  is calculated by the sensing unit  4  arranged in the end portion of the flow passage  2  and the flow-volume-force correspondence relation information  531  stored in a memory unit  53 . 
     Thus, it is possible to provide an undersized and inexpensive force calculation system, which calculates strength of force applied to a target area without an electrical device. 
     More specifically, a sensing unit  4  may be implemented by either a tucked tube type or a slit type. 
     In addition, as targeted detection is air volume, this is able to normally use under the electromagnetic environment such as the MRI device or explosion-proof environment such as a nuclear power plant. 
     Furthermore, as the sensing unit  4  has simple structure, it is possible to miniaturize it, to reduce parts count, and to achieve low cost and high durability. 
     To apply a surgical robot, as the end of a forceps has a diameter size of about 10 mm, it is possible to provide the sensing unit with the forceps. 
     In addition, in the environment that there is a permanently-installed air pressure source (the air blowing unit  1 ) such as a hospital, it is possible to compactify the whole system using the air blowing unit  1 . 
     Furthermore it is possible to withstand high temperature sterilization treatment in about 125° C., since a sensing unit  4  is made of metal material such as stainless steel or aluminum. Thus this invention is suitable for applying to a medical field. 
     In addition, the system of this invention has high degrees of freedom of placement position, since the sensing unit  4  is connected to the flowmeter  3 . More specifically, when using an optical fiber sensor, it is possible to disturb a movement of an articulated surgical robot due to rigidity of optical fibers with this robot. 
     On the other hand, in this embodiment, it is possible to use a low rigidity material for flow passage  2 , thus it is possible to avoid this problem. 
     (Another Variation) 
     Next, another variation of a sensing unit  4  is explained. 
     As shown in  FIG. 7A , a tucked tube type sensing unit  4   c  tucks three flow passages  2   a ,  2   b  and  2   c  at different positions in the aperture  41 . In this case, for example, three flow passages  2   a    2   b  and  2   c  have flowmeters  3  respectively, and the flowmeters  3  measure the flow volumes of the flow passages  2   a ,  2   b  and  2   c  respectively. 
     In this case, it is possible to calculate respectively the strength of external force based on the flow-volume-force correspondence relation information  531  stored in memory unit  53  and the flow volumes of air flowing through the flow passages  2   a    2   b  and  2   c . Thus, in the processing unit  52 , it is possible to calculate the direction and the strength of external force applied to the sensing unit  4   c  based on this information. In addition, the system is able to have each flow-volume and force correspondence relation information corresponding to each of flow passages  2   a ,  2   b  and  2   c.    
     In addition, as shown in  FIG. 7B , in a slit type sensing unit  4   d , the flow passages  2   d ,  2   e  and  2   f  are arranged at deferent positions. In this case, for example, three flow passages  2   d ,  2   e  and  2   f  have respectively flowmeters  3 , and the flowmeters  3  measure the flow volumes of the flow passages  2   d ,  2   e  and  2   f  respectively. 
     In this case, it is possible to calculate respectively the strength of external force, based on the flow-volume-force correspondence relation information  531  stored in memory unit  53  and flow volumes of air flowing through the flow passages  2   d    2   e  and  2   f . And, in the processing unit  52 , it is possible to calculate the direction and the strength of external force applied to the sensing unit  4   c  based on this information. In addition, the system is able to have each flow-volume and force correspondence relation information corresponding to each of flow passages  2   d ,  2   e  and  2   f.    
     As mentioned above, according to another variation of a sensing unit, it is possible to calculate a direction and strength of force applied to one sensing unit, using a plurality of flow passages. 
     This invention is not limited to above embodiment. For example, material of the sensing unit  4  is not limited to the above embodiment. For example, it is possible to use another elastically deformable material such as titanium or plastic for the sensing unit  4 . 
     In addition, as a sample of a coil spring is explained regarding the tucked tube type sensing unit  4 , the sensing unit  4  is not limited to this structure. For example, it is possible to use another elastic body, which makes the width of the aperture change as a function of external force, such as a leaf spring or short spring. 
     In addition, as a sample of a computer is explained regarding the computing device  5 , it is possible to use a LSI or an IC integrated the receiving unit  51 , the receiving unit  52  and the processing unit  53  etc. 
     In addition, the shape of the sensing unit  4   b  is limited to a cylindrical shape. For example, it is possible to use another shape such as polygonal shape for the shape of the sensing unit  4   b.    
     Furthermore it is possible to have two slit in the helical slit  42  and to close the opening in the bottom of the sensing unit  4   b.    
     In addition, in this embodiment, the sensing unit  4  is explained when it is applied to the force pushing it. However, it is possible to use a sensing unit  4  applied to the force pulling it. In this case, along with above information shown in  FIGS. 4A and 4B , it is necessary to obtain corresponding relationship between force and the flow volume under the condition that force is negative. 
     Regarding structures such as hardware or flowchart, it is possible to modify structures appropriately, if the scope of the present invention is not changed. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
       1  air blowing unit 
       2  flow passage 
       3  flowmeter 
       4  sensing unit 
       5  computing device 
       21  end portion 
       22  middle portion 
       41  aperture 
       42  slit 
       43  facing plane 
       51  receiving unit 
       52  processing unit 
       53  memory unit 
       54  input unit 
       55  output unit 
       100  force calculation system 
       531  flow-volume-force correspondence relation information (in figures, abbreviated to “FF information”)