JP2014104131A - Design method for syringe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently design the shape of a tip part of a plunger.SOLUTION: A method for designing a medical solution filling type syringe H using a computer 1. The design method includes: a first deformation calculation step S3 of calculating a deformation shape of a gasket model 26 when only the gasket model 26 is mounted in a barrel model 21 in the compressed state, by a computer 1; a step S4 of designing a shape of a tip part 16 of a plunger 4 according to the shape of a recessed part 28 of the compressed gasket model 26; a second deformation calculation step S6 of inserting the tip part 34 of a plunger model 31 in the recessed part 28 of the compressed gasket model 26 and calculating the physical amount related to the sliding resistance F2 of the gasket model 26; and a step S8 of evaluating the shape of the tip part 16 of the plunger 4 based upon the physical amount.

Description

  The present invention relates to a method for designing a syringe that can efficiently design the shape of the tip of a plunger.

  As shown in FIG. 2, in the medical field, a syringe H pre-filled with a drug solution M is widely used. This type of syringe H is mounted in a compressed state on the cylindrical barrel 2 having an outlet 7 to which an injection needle can be connected at one end T1, a cap body 10 for closing the outlet 7, and the other end T2 of the barrel 2. And the plunger 4 that injects the chemical M from the outlet 7 by pushing the gasket 3 toward the one end T1. Further, a recess 11 is formed on the surface of the other end T2 of the gasket 3. The tip end 16 of the plunger 4 is inserted into the recess 11.

  In the manufacturing process of the syringe H, the drug solution M is injected into the barrel 2. The chemical M is sealed with a cap body 10 and a gasket 3 attached to the barrel 2. Next, the tip portion 16 of the plunger 4 is inserted into the recess 11 of the gasket 3. Related literature includes:

JP 2012-147859 A

  In general, the distal end portion 16 of the plunger 4 is designed based on the shape of the concave portion 11 of the gasket 3. However, as shown in FIG. 15, when the gasket 3 is attached to the barrel 2 in a compressed state, the inner diameter D3 of the recess 11 is smaller than before the attachment, so that the distal end portion 16 of the plunger 4 is There was a problem that it was difficult to insert into the recess 11.

  Even when the distal end portion 16 of the plunger 4 is inserted into the concave portion 11, the outer surface 16 o of the distal end portion 16 presses the inner side surface 11 i of the concave portion 11 radially outward, and the gasket 3 and the barrel 2 slide. Resistance may increase. This reduces the sliding performance of the gasket 3. Thus, since it is difficult to specify the shape of the tip portion 16 of the plunger 4 at the design stage of the syringe, a syringe design method that can efficiently design the shape of the tip portion 16 has been strongly demanded.

  The present invention has been devised in view of the above circumstances, and has as its main object to provide a method for designing a syringe that can efficiently design the shape of the tip of the plunger.

  The invention according to claim 1 of the present invention includes a cylindrical barrel having an opening that can be connected to an injection needle on one end side and an opening on the other end side, and compression on the other end side of the barrel. The gasket is mounted in a state and a recess is formed on the surface on the other end side, and a tip is inserted into the recess of the gasket and the gasket is pushed toward the one end side to inject the chemical solution from the outlet. For a chemical solution filling type in which a chemical solution is pre-filled in an airtight space of the barrel in which the outlet is closed with a cap body and the opening is closed with the gasket. A method of designing a syringe using a computer, wherein a barrel model obtained by modeling the barrel with a finite number of elements is input to the computer; Inputting a gasket model in which the gasket having the recess is modeled by a finite number of elements, and the computer is configured to input the gasket when only the gasket model is attached to the barrel model in a compressed state. A first deformation calculating step of calculating a deformed shape of the model; a step of designing a shape of the tip portion of the plunger based on the shape of the concave portion of the gasket model in the compressed state; A step of inputting a plunger model in which the tip of the plunger is modeled by a finite number of elements; and the computer inserts the tip of the plunger model into the recess of the gasket model in the compressed state, Regarding the sliding resistance when the gasket model is moved to the one end The second deformation calculation step of calculating the physical quantity, and, on the basis of the physical quantity, characterized in that it comprises a step of evaluating the shape of the tip portion of the plunger.

  The invention according to claim 2 is the syringe design method according to claim 1, wherein the barrel model, the gasket model, and the plunger model are two-dimensional models based on a cross-sectional shape including a central axis of the barrel. It is.

  According to a third aspect of the present invention, in the first deformation calculation step, the inner diameter of the barrel model is increased, the diameter increasing step for disposing the gasket model inside thereof, and the gasket model being disposed. 3. A method for designing a syringe according to claim 1, further comprising a diameter reducing step of performing deformation calculation of the gasket model by returning the inner diameter of the barrel model.

  According to the syringe designing method of the present invention, the computer calculates a deformed shape of the gasket model when only the gasket model is attached to the barrel model in a compressed state, and a concave portion of the compressed gasket model. And designing the shape of the tip of the plunger based on the shape of the plunger.

  Further, in the design method of the present invention, the step of inputting a plunger model in which the tip end of the designed plunger is modeled by a finite number of elements to a computer, the tip end of the plunger model is inserted into the recess, and the gasket model is inserted. A second deformation calculating step of calculating a physical quantity related to sliding resistance when the is moved to one end side, and a step of evaluating the shape of the tip of the plunger based on the physical quantity.

  As described above, in the design method of the present invention, it is possible to design the distal end portion of the plunger that can be reliably inserted into the recessed portion of the compressed gasket by simulation using a computer. Moreover, in the design method of the present invention, since the shape of the tip of the plunger is evaluated based on the physical quantity relating to the sliding resistance of the gasket, it is possible to design a syringe with excellent plunger sliding performance.

It is a perspective view of the computer which performs the design method of this embodiment. It is a side view of a syringe. It is a fragmentary sectional view of the syringe which decomposes | disassembles and shows a barrel, a gasket, and a plunger. It is a flowchart which shows the design method of this embodiment. It is a top view which visualizes and shows a barrel model. It is a top view which visualizes and shows a gasket model. It is a flowchart which shows the 1st calculation step of this embodiment. (A), (b) is a top view explaining a diameter expansion step, (c) is a top view explaining a diameter reduction step. It is a top view explaining the step which designs the shape of the front-end | tip part of a plunger. It is a top view which visualizes and shows a plunger model. It is a flowchart which shows the 2nd calculation step of this embodiment. (A) is a top view which shows the plunger which inserted the front-end | tip part in the recessed part of a gasket model, (b) is a top view which shows the gasket model 26 which moved to the one end side. It is a contour figure of the contact stress of a gasket model. It is a graph which shows the relationship between the movement amount of a gasket model, and the sliding resistance of a gasket model. FIG. 3 is a cross-sectional view of the syringe of FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The syringe design method of the present embodiment (hereinafter sometimes simply referred to as “design method”) is a method for efficiently designing the shape of the tip of the plunger of the syringe using a computer.

  As shown in FIG. 1, the computer 1 includes a main body 1a, a keyboard 1b, a mouse 1c, and a display device 1d. The main body 1a is provided with an arithmetic processing unit (CPU), a ROM, a working memory, a storage device such as a magnetic disk, and disk drive devices 1a1, 1a2. Note that a processing procedure (program) for executing the design method of the present embodiment is stored in the storage device in advance.

  As shown in FIG. 2, the syringe H includes a barrel 2, a gasket 3 attached to the barrel 2 in a compressed state, and a plunger 4 for injecting the drug solution M from the barrel 2. The syringe H according to the present embodiment is used for a chemical solution filling type in which the airtight space of the barrel 2 is filled with the chemical solution M in advance.

The barrel 2 has a cylindrical main body portion 6 filled with a chemical M, an outlet 7 to which an injection needle (not shown) can be connected to one end side T1 of the main body portion 6, and the other end side T2 of the main body portion 6 released. And a flange 9 extending like a bowl on the other end T2 of the main body 6. Further, the barrel 2 is detachably provided with a cap body 10 that closes the outlet 7.

  The gasket 3 is made of an elastic body such as rubber, for example. As shown in FIG. 3, the gasket 3 is formed in a substantially cylindrical shape whose maximum outer diameter D <b> 2 is larger than the inner diameter D <b> 1 of the main body 6 of the barrel 2 before being attached to the barrel 2.

  Such a gasket 3 is inserted into the other end side T <b> 2 of the barrel 2 in a compressed state by being inserted from the opening 8 of the barrel 2. Thereby, the space in the barrel 2 is kept airtight. Further, a bottomed recess 11 to which the plunger 4 is attached is formed on the surface 3S of the other end T2 of the gasket 3. The recess 11 is formed in a cylindrical shape.

  As shown in FIG. 2, the plunger 4 has a rod-like base portion 15, a distal end portion 16 inserted into the recess 11 of the gasket 3 at one end side T <b> 1 of the base portion 15, and a bowl shape at the other end side T <b> 2 of the base portion 15. And a flange 17 that extends. As shown in FIG. 3, the tip 16 is formed in a cylindrical shape having an outer diameter D4 that is smaller than the inner diameter D3 of the recess 11 of the gasket 3 before being attached to the barrel 2.

  As shown in FIG. 2, such a plunger 4 is inserted into the recess 11 of the gasket 3 and an external force F1 applied to the one end T1 is applied to push the gasket 3 toward the one end T1. Can be slid. By the sliding of the gasket 3, the chemical solution M filled in the barrel 2 can be injected from the outlet 7.

  FIG. 4 shows a specific procedure of the design method of the present embodiment. In the present embodiment, first, a barrel model obtained by modeling the barrel 2 (shown in FIG. 2) is input to the computer 1 (step S1).

  As shown in FIG. 5, the barrel model 21 is set by modeling (discretizing) the barrel 2 shown in FIG. 2 with a finite number of elements 22 that can be handled by a numerical analysis method. As a numerical analysis method, a finite element method is employed in this embodiment.

  As shown in FIG. 2, the barrel 2 has rotational symmetry about the central axis C thereof. Therefore, as shown in FIG. 5, the barrel model 21 is set as a two-dimensional model based on a cross-sectional shape including the central axis C of the barrel 2. Since the barrel model 21 of this embodiment is defined by half with respect to the central axis C, the number of elements 22 can be significantly reduced as compared with the three-dimensional model, and the calculation time can be shortened. A fixed boundary condition is set for the central axis C.

  The barrel model 21 of the present embodiment includes a part of the other end T2 of the main body 6 and the opening of the main body 6, the outlet 7, the opening 8, and the flange 9 of the barrel 2 shown in FIG. A main body 23 and an opening 24 that model only 8 are included. Thus, since the barrel model 21 is modeled by limiting only a part of the main body 6 and the opening 8, the time required for modeling and the calculation time are reduced. In step S1, the inner diameter D5 of the main body 23 of the barrel model 21 is set to be the same as the inner diameter D1 (shown in FIG. 3) of the main body 6 of the barrel 2.

  A quadrilateral element is used as the element 22 of this embodiment, but other than this, for example, a triangular element suitable for expressing a complicated shape may be used. Each element 22 includes numerical data such as an element number, a node 22s number, a coordinate value of the node 22s, and material characteristics (for example, density, Young's modulus, damping coefficient, etc.) of the barrel 2 (shown in FIG. 2). Is defined. These numerical data are stored in the computer 1.

  Next, a gasket model obtained by modeling the gasket 3 (shown in FIG. 2) is input to the computer 1 (step S2).

  As shown in FIG. 6, the gasket model 26 is set by modeling (discretizing) with a finite number of elements 27, similarly to the barrel model 21. As shown in FIG. 2, the gasket 3 has rotational symmetry about the central axis C of the barrel 2, similar to the barrel 2. For this reason, as shown in FIG. 6, the gasket model 26 is also set as a two-dimensional model based on a cross-sectional shape including the central axis C of the barrel 2.

  In addition, the gasket model 26 is provided with a recess 28 as in the gasket 3 (shown in FIG. 2). In this step S2, the outer diameter D6 of the gasket model 26 is set to be the same as the maximum outer diameter D2 (shown in FIG. 3) of the gasket 3 before mounting. Furthermore, the inner diameter D7 of the recess 28 is set to be the same as the inner diameter D3 (shown in FIG. 3) of the gasket 3 before mounting.

  The element 27 is the same as the element 22 of the barrel model 21, and the element number, the number of the node 27s, the coordinate value of the node 27s, and the material properties (for example, density, Young's modulus or damping coefficient) of the gasket 3 (shown in FIG. 2). Etc.) are defined. These numerical data are stored in the computer 1.

  Next, a first deformation calculation step S3 is performed in which the computer 1 calculates a deformation shape of the gasket model 26 when only the gasket model 26 is mounted on the barrel model 21 in a compressed state. FIG. 7 shows a specific processing procedure of the first deformation calculation step S3 of the present embodiment.

  In the first deformation calculation step S3 of the present embodiment, first, a diameter expansion step S31 for increasing the inner diameter D1 of the barrel model 21 is performed. In this diameter expansion step S31, as shown in FIG. 8A, the inner diameter D5 of the main body portion 23 of the barrel model 21 is the inner diameter D1 of the barrel model 21 in step S1, and the gasket model 26 in step S2. Is set larger than the outer diameter D6 (shown in FIG. 8B). Then, as shown in FIG. 8B, the gasket model 26 is disposed inside the barrel model 21 whose diameter has been expanded. In this diameter expansion step S31, the inner diameter D5 of the barrel model 21 can be appropriately set as long as it is larger than the outer diameter D6 of the gasket model 26, for example.

  Next, a diameter reduction step S32 for returning the inner diameter D5 of the barrel model 21 is performed. In this diameter reduction step S32, as shown in FIG. 8C, the inner diameter D5 of the main body 23 of the barrel model 21 is restored so as to be the same as the inner diameter D1 of the barrel model 21 in step S1. Since a fixed boundary condition is set in the central axis C, the gasket model 26 is pressed radially inward by the main body portion 23 of the barrel model 21, and the compression deformation of the gasket model 26 is calculated. By calculating such compression deformation, the deformation shape of the gasket model 26 attached to the barrel model 21 in a compressed state can be calculated. Further, due to the compression deformation of the gasket model 26, the recess 28 is deformed into a recess 28 (shown in FIG. 8B) before the compression deformation.

  In the deformation calculation of the gasket model 26, the mass matrix, stiffness matrix and damping matrix of the element 27 are created based on the shape and material properties of each element 27 (shown in FIG. 6), and these matrices are combined. A matrix of the entire system is created. Then, the computer 1 creates equations of motion by applying various conditions, and performs deformation calculation of the gasket model 26 every unit time Tx (x = 0, 1,...) (For example, every 1 μsec). . Such deformation calculation can be performed using commercially available finite element analysis application software such as LS-DYNA manufactured by JSOL, for example.

  In the first deformation calculation step S3 of the present embodiment, the gasket model 26 attached to the barrel model 21 in a compressed state can be set by calculating only the radially inward compression deformation of the gasket model 26. Thereby, in this embodiment, compared with the case where the gasket model 26 is inserted into the opening 24 of the barrel model 21 and the deformation calculation is performed, for example, the calculation of the sliding friction between the gasket model 26 and the barrel model 21 is performed. Can be omitted. Accordingly, the first modification calculation step S3 of the present embodiment reduces the calculation time.

  In the first deformation calculation step S3, the deformation calculation may be performed by inserting the gasket model 26 into the opening 24 of the barrel model 21 as described above. According to such a method, the deformation calculation of the gasket model 26 can be performed in a more realistic approximation, so that the simulation accuracy can be improved.

  Next, as shown in FIG. 9, step S4 for designing the shape of the distal end portion 16 of the plunger 4 based on the shape of the concave portion 28 of the compressed gasket model 26 is performed. In this step S4, the outer diameter D4 of the distal end portion 16 of the plunger 4 is set smaller than the inner diameter D7 of the concave portion 28 of the compressed gasket model 26. Thereby, in step S4 of this embodiment, the front-end | tip part 16 which can be reliably inserted in the recessed part 11 (shown in FIG. 3) of the gasket 3 of a compression state can be designed.

  Further, since the outer diameter D4 of the distal end portion 16 of the plunger 4 is set smaller than the inner diameter D3 of the recessed portion 28 of the compressed gasket model 26, a gap 29 is formed between the distal end portion 16 and the recessed portion 28. The The gap 29 can suppress the distal end portion 16 of the plunger 4 from pressing the inner side surface 28 i of the concave portion 28 radially outward. Therefore, since the designed plunger 4 can suppress an increase in sliding resistance between the outer surface 3o (shown in FIG. 2) of the gasket 3 and the inner surface 2i (shown in FIG. 2) of the barrel 2, the sliding of the gasket 3 is suppressed. Performance can be improved. The inner diameter D3 is specified as a minimum value when it changes in the recess 28.

  Next, a plunger model obtained by modeling the tip 16 of the designed plunger 4 is input to the computer 1 (step S5).

  As shown in FIG. 10, the plunger model 31 is set by modeling (discretizing) the plunger 4 with a finite number of elements 32, similarly to the barrel model 21 and the gasket model 26. As shown in FIG. 2, the plunger 4 has rotational symmetry about the central axis C of the barrel 2, like the barrel 2 and the gasket 3. For this reason, as shown in FIG. 10, the plunger model 31 is also set as a two-dimensional model based on a cross-sectional shape including the central axis C of the barrel 2.

  The plunger model 31 of the present embodiment includes a base portion 33 in which only one end side T1 of the base portion 15 and only the distal end portion 16 among the base portion 15, the distal end portion 16 and the flange 17 shown in FIG. A tip 34 is included. Thus, since the plunger model 31 is modeled by limiting only a part of the one end side T1 of the base portion 15 and the tip end portion 16, the calculation time is shortened.

  Each element 32 is defined with numerical data such as an element number, a node 32s number, a coordinate value of the node 32s, and a material property of the plunger 4 (for example, density, Young's modulus or damping coefficient). These numerical data are stored in the computer 1.

  Next, the computer 1 calculates a physical quantity related to the sliding resistance of the gasket model 26 (second deformation calculation step S6). FIG. 11 shows a specific processing procedure of the second deformation calculation step S6 of the present embodiment.

  In the second deformation calculation step S6, first, as shown in FIG. 12A, the computer 1 inserts the distal end portion 34 of the plunger model 31 into the recessed portion 28 of the compressed gasket model 26 (step S61). ). In step S61 of this embodiment, the plunger model 31 and the barrel model 21 are aligned with the central axis C, and the tip portion 34 is inserted into the recess 28. The outer diameter D4 (shown in FIG. 9A) of the tip 34 of the plunger 4 is set smaller than the inner diameter D3 (shown in FIG. 9A) of the recess 28 of the compressed gasket model 26. The tip portion 34 can be smoothly inserted into the recess 28.

  Next, as shown in FIG. 12B, the computer 1 calculates a physical quantity related to the sliding resistance F2 when the gasket model 26 is moved to the one end T1 (step S62). In this step S62, first, an external force F1 directed to one end T1 is defined in the plunger model 31. Accordingly, it is possible to calculate a state in which the gasket model 26 is pressed by the plunger model 31 and moves to the one end T1 while sliding on the inner surface 21i of the barrel model 21.

  In the deformation calculation accompanying the movement of the gasket model 26, as in the first deformation calculation step S3, the computer 1 creates various equations of motion by applying various conditions, and these are expressed as unit time Tx (x = 0). ,...) (For example, every 1 μs), the deformation calculation of the gasket model 26 is performed. Thereby, the physical quantity regarding the sliding resistance F2 when moving the gasket model 26 to the one end side T1 can be calculated | required. The physical quantity related to the sliding resistance F2 includes the sliding resistance (friction force) F2 itself, the contact stress of the gasket model 26, which is one of the parameters for obtaining the sliding resistance F2. In the present embodiment, the sliding resistance (friction force) F2 and the contact stress of the gasket model 26 are obtained.

  Next, the computer 1 determines whether a predetermined end time has elapsed (step S63). In step S63, when it is determined that the end time has elapsed, the second deformation calculation step S6 is ended, and the physical quantity related to the sliding resistance F2 of the gasket model 26 is output (step S7).

  On the other hand, when the computer 1 determines that the end time has not elapsed, the unit time Tx is advanced by one (step S64), and steps S62 to S63 are performed. Thereby, in this embodiment, the physical quantity regarding the sliding resistance F2 of the gasket model 26 is acquirable for every unit time Tx from the movement start of the gasket model 26 to completion | finish.

  Examples of the physical quantity output in step S7 include a contact stress contour diagram of the gasket model 26 (shown in FIG. 13), a movement amount of the gasket model 26, and an outer surface 26o of the gasket model 26 (shown in FIG. 10B). The graph (shown in FIG. 14) showing the relationship with the sliding resistance F2 measured in (1) is included.

  Next, the shape of the distal end portion 34 of the plunger model 31 is evaluated based on the physical quantity related to the sliding resistance F2 of the gasket model 26 (step S8). In this step S8, first, the contact stress acting on the gasket model 26 is evaluated from the contact stress contour diagram shown in FIG.

  As is apparent from FIG. 13, the gasket model 26 of the present embodiment has a small contact stress on the radially outer side of the recess 28. This is considered to be because the outer diameter D4 of the distal end portion 16 of the plunger 4 is designed to be smaller than the inner diameter D3 of the concave portion 28 of the gasket model 26 in the compressed state. Thus, when the contact stress of the gasket model 26 is reduced, the sliding resistance F2 can be reduced, and the sliding performance can be improved. On the other hand, when the contact stress of the gasket model 26 is large, the sliding resistance F2 increases, and the sliding performance decreases. From such a contour diagram, the shape of the tip 16 of the plunger 4 can be evaluated.

  Next, it is confirmed from the graph shown in FIG. 14 whether or not the sliding resistance F2 on the outer surface 26o of the gasket model 26 is within the threshold range. If the sliding resistance F2 is within a predetermined threshold, it can be confirmed that the shape of the designed tip portion 16 of the plunger 4 can improve the sliding performance. On the other hand, when the sliding resistance F2 exceeds a predetermined threshold value, it can be confirmed that the sliding performance cannot be sufficiently improved with the designed shape of the tip portion 16 of the plunger 4. In addition, the threshold value of this embodiment is 7.0N.

  In step S8, when it is determined by the above evaluation that the shape of the tip 16 of the designed plunger 4 is good, the plunger 4 is manufactured based on the shape of the tip 16 (step S9).

  On the other hand, when it is determined that the shape of the tip portion 16 of the designed plunger 4 is defective, the shape of the tip portion 16 is changed (step S10), and steps S5 to S8 are performed again.

  Thus, in this embodiment, since the shape of the tip 16 of the designed plunger 4 is evaluated based on the physical quantity related to the sliding resistance F2 of the gasket model 26, the syringe H having excellent sliding performance can be efficiently used. Can be designed.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  The shape (outer diameter D4: 4.40 mm) of the tip of the plunger was designed according to the processing procedure shown in FIG. 4 (Example). A syringe was manufactured based on the shape of the tip of the plunger of this example.

  For comparison, the shape of the plunger tip (outer diameter D4: 4.90 mm) was designed based on the shape of the recess before the gasket was mounted on the barrel (comparative example). A syringe was manufactured based on the shape of the tip of the plunger of this comparative example.

  And in the syringe of an Example and a comparative example, it was confirmed by the tester's visual observation whether the front-end | tip part of a plunger can be inserted in the recessed part of a gasket. Further, in the syringes of Examples and Comparative Examples, the sliding performance of the gasket was evaluated by the sensory function. The common specifications are as follows.

Barrel inner diameter D1: 8.65mm
Gasket (before compression):
Maximum outer diameter D2: 8.95mm
Inner diameter D3 of recess: 5.00 mm
External force F1: 8.0 (N)

  As a result of the test, it was confirmed that the tip of the plunger of the example could be smoothly inserted into the recess of the gasket attached to the barrel. On the other hand, the tip of the plunger of the comparative example could not be inserted into the recess of the gasket attached to the barrel. Furthermore, it was confirmed that the syringe of the example was excellent in the sliding performance of the gasket. Therefore, it was confirmed that the design method of the example can efficiently design the shape of the tip of the plunger.

21 Barrel model 26 Gasket model 28 Recess 31 Plunger model 34 Tip

Claims (3)

A cylindrical barrel having an opening to which an injection needle can be connected at one end and an opening having the other end opened;
A gasket attached to the other end of the barrel in a compressed state and having a recess formed on the other end; and
A rod-shaped plunger for injecting a chemical solution from the outlet by pushing the gasket toward the one end side while the distal end portion is inserted into the concave portion of the gasket,
Moreover, in order to design, using a computer, a medical solution filling type syringe in which the outlet is closed with a cap body and the opening is closed with the gasket, and the hermetic space of the barrel is pre-filled with a medical solution. The method of
Inputting to the computer a barrel model obtained by modeling the barrel with a finite number of elements;
Inputting to the computer a gasket model in which the gasket having the recess is modeled by a finite number of elements;
A first deformation calculating step in which the computer calculates a deformed shape of the gasket model when only the gasket model is mounted in a compressed state on the barrel model;
Designing the shape of the tip of the plunger based on the shape of the recess of the gasket model in the compressed state;
Inputting to the computer a plunger model obtained by modeling the designed tip of the plunger with a finite number of elements;
The computer calculates a physical quantity related to sliding resistance when the distal end portion of the plunger model is inserted into the concave portion of the gasket model in the compressed state and the gasket model is moved to the one end side. Two deformation calculation steps; and
A method for designing a syringe, comprising a step of evaluating a shape of the tip of the plunger based on the physical quantity.   The syringe design method according to claim 1, wherein the barrel model, the gasket model, and the plunger model are two-dimensional models based on a cross-sectional shape including a central axis of the barrel.   In the first deformation calculation step, the inner diameter of the barrel model is increased, the diameter increasing step for disposing the gasket model inside thereof, and after the gasket model is disposed, the inner diameter of the barrel model is restored. The method for designing a syringe according to claim 1, further comprising a diameter reduction step of calculating deformation of the gasket model.