Injection device

Abstract

The screw (12) of the injection device (10) of one embodiment has a plurality of peripheral projections (50) each of which has a peripheral projection slope (50S) and a second peripheral projection slope (50SS) formed therein. The bushing (14) of the injection device (10) has a plurality of inner peripheral projections (60) each of which has an inner peripheral projection slope (60S) and a second inner peripheral projection slope (60SS) formed therein. There are no flats at the rear end of each of the plurality of peripheral projections (50) and at the front end of each of the plurality of inner peripheral projections (60).

Description

Technical Field

[0001] This invention relates to injection devices. Background Technology

[0002] Japanese Patent Application Publication No. 2019-055488 discloses a motor control unit for controlling a linear motion motor and a rotary motion motor. The linear motion motor is a motor that moves a bushing along the axial direction of a screw. The rotary motion motor is a motor that rotates the bushing about the axis of the screw.

[0003] The motor control unit controls the linear motion motor to move the bushing from a state separated from the screw towards the screw. During the bushing's forward movement, when the torque of the linear motion motor reaches or exceeds a first torque, the motor control unit controls the rotary motion motor to rotate the bushing. Summary of the Invention

[0004] However, in order to improve the efficiency of spline engagement, it is required that spline engagement be performed solely by advancing the bushing relative to the screw, without rotating the bushing.

[0005] Therefore, the present invention provides an injection device that can improve the efficiency of spline fitting.

[0006] The present invention provides an injection device comprising: a screw arranged in a front-to-back direction, wherein the front direction for injecting injection resin is a direction opposite to the front direction, and a bushing formed to engage with the spline of the screw, wherein...

[0007] The screw has a plurality of peripheral protrusions formed on the outer peripheral surface of the rear end side of the screw, and extending at intervals along the front-rear direction in the circumferential direction of the screw.

[0008] The plurality of peripheral protrusions are each formed with: a peripheral protrusion ramp, which is inclined such that the width of the peripheral protrusion along the circumference of the screw decreases as it approaches the rear end of the peripheral protrusion; and a second peripheral protrusion ramp, which is inclined such that the outer diameter of the screw decreases as it approaches the rear end of the peripheral protrusion.

[0009] The bushing has: a through hole extending in the front-rear direction; and a plurality of inner peripheral protrusions formed on the inner peripheral surface of the through hole and extending at intervals along the front-rear direction in the circumferential direction of the through hole.

[0010] The plurality of inner circumferential protrusions are each formed with: an inner circumferential protrusion slope, which is inclined such that the width of the inner circumferential protrusion along the circumference of the through hole decreases as it approaches the front end of the inner circumferential protrusion; and a second inner circumferential protrusion slope, which is inclined such that the inner diameter of the bushing increases as it approaches the front end of the inner circumferential protrusion.

[0011] There is no plane at the rear end of each of the plurality of peripheral protrusions and at the front end of each of the plurality of inner peripheral protrusions.

[0012] According to the method of the present invention, spline engagement can be achieved by the forward movement of the bushing relative to the screw without rotating the bushing. As a result, the efficiency of spline engagement can be improved. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating an injection device according to one embodiment.

[0014] Figure 2 This is a diagram showing the screw and bushing.

[0015] Figure 3A It means Figure 2 A diagram of the screw cross-section. Figure 3B It means Figure 2 A diagram of the bushing cross-section.

[0016] Figure 4 This is a flowchart illustrating the control process executed by the motor control unit to engage the screw with the bushing spline.

[0017] Figure 5 This is a diagram showing the screw and bushing of modified Example 1. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings, following preferred embodiments.

[0019] [Implementation Method]

[0020] Figure 1 This is a schematic diagram showing an injection apparatus 10 according to one embodiment. The injection apparatus 10 injects molding resin into a mold. In this embodiment, the injection direction of the molding resin is set as the forward direction, and the opposite direction is set as the rearward direction. The injection apparatus 10 includes: a screw 12, a bushing 14, a bushing fastening part 16, and a drive mechanism 18.

[0021] The screw 12 is housed in the through hole 20H of the cylinder 20. The screw 12, by rotating, conveys the molding resin fed into the through hole 20H forward. A nozzle 22 is provided at the front end of the cylinder 20, and the molding resin conveyed by the screw 12 is ejected from the nozzle 22. The screw 12 has a screw portion 12A and a spline portion 12B.

[0022] The screw portion 12A is the front part of the screw 12. A helical protrusion 12P is formed on the outer peripheral surface of the screw portion 12A. The spline portion 12B is the rear part of the screw 12 and is connected to the rear end of the screw portion 12A. The outer peripheral surface of the spline portion 12B has a groove and a protrusion that can engage with the spline of the bushing 14.

[0023] The bushing 14 is splinedly engaged with the screw 12. The bushing 14 has a through hole 14H that extends in the front-rear direction. The inner circumferential surface of the through hole 14H is formed with a concave-convex shape so as to engage with the spline portion 12B. The bushing 14 is provided with an annular protrusion 14A that protrudes rearward from the rear end face of the bushing 14.

[0024] The bushing fastener 16 secures the bushing 14 to the rear of the bushing 14. The bushing fastener 16 has a recess 16A that receives the protrusion 14A of the bushing 14. The bushing 14, in which the protrusion 14A is received in the recess 16A, is secured to the bushing fastener 16 by bolts.

[0025] The drive mechanism 18 is a mechanism that drives at least one of the screw 12 and the bushing 14 to move the bushing 14 relative to the screw 12. In this embodiment, the drive mechanism 18 drives the bushing 14. The drive mechanism 18 includes a direct-drive motor 24, a rotary motor 26, and a motor control unit 28.

[0026] The direct-drive motor 24 is a motor that moves the bushing 14 forward and backward in the front-to-back direction. A ball screw 30, which rotates with the motor shaft, is connected to the motor shaft of the direct-drive motor 24. A sliding part 32 is installed on the ball screw 30 to allow the ball screw 30 to move forward and backward in the front-to-back direction according to the rotation of the direct-drive motor 24. A direct-drive gear 34 is rotatably mounted on the sliding part 32. The direct-drive gear 34 is fixed to the rear end of the bushing fastener 16. The direct-drive motor 24 is equipped with an encoder 36 for detecting the rotation angle of the direct-drive motor 24 and a detection part 38 for detecting the direct-drive torque of the direct-drive motor 24.

[0027] The rotary motor 26 is a motor that rotates the bushing 14. The rotary gear 40, which meshes with the direct-drive gear 34, is connected to the motor shaft of the rotary motor 26. An encoder 42 is provided in the rotary motor 26 to detect the rotation angle of the rotary motor 26.

[0028] In the drive mechanism 18, when the direct-drive motor 24 rotates, the direct-drive gear 34 moves in the front-to-back direction via the ball screw 30 and the sliding part 32 according to the rotation of the direct-drive motor 24. In this case, the rotary gear 40 meshing with the direct-drive gear 34 and the rotary motor 26 move in the front-to-back direction, and the bushing 14 moves in the front-to-back direction via the bushing fastening part 16 that fixes the direct-drive gear 34. On the other hand, when the rotary motor 26 rotates, the rotary gear 40 rotates according to the rotation of the rotary motor 26. In this case, the direct-drive gear 34 meshing with the rotary gear 40 rotates, and the bushing 14 rotates via the bushing fastening part 16 that fixes the direct-drive gear 34.

[0029] The motor control unit 28 controls the linear motor 24 to make the rotation angle detected by the encoder 36 reach the target value, thereby causing the bushing 14 to move forward and backward. Additionally, the motor control unit 28 controls the rotary motor 26 to make the rotation angle detected by the encoder 42 reach the target value, thereby causing the bushing 14 to rotate.

[0030] In addition, the motor control unit 28 performs control processing while monitoring the direct torque detected by the detection unit 38 and controlling only the direct motor 24, thereby enabling the screw 12 to engage with the bushing 14 spline.

[0031] Figure 2 This is a diagram showing the screw 12 and the bushing 14. Figure 3A It means Figure 2 A cross-sectional view of screw 12. Figure 3B It means Figure 2 A cross-sectional view of bushing 14.

[0032] A plurality of peripheral protrusions 50 are formed on the outer peripheral surface of the spline portion 12B, which extend in the front-rear direction at intervals in the circumferential direction of the spline portion 12B. Each of the peripheral protrusions 50 is divided by a fitting groove 52 that surrounds the spline portion 12B in the circumferential direction. An annular retainer 46 ( Figure 1 It is fitted into the fitting groove 52.

[0033] Each of the plurality of peripheral protrusions 50 has the same shape. The following description relating to the shape of the peripheral protrusion 50 pertains to only one of the plurality of peripheral protrusions 50. The rear end of the peripheral protrusion 50 is formed into a pointed shape or a rounded shape. That is, there is no flat surface at the rear end of the peripheral protrusion 50 of the screw 12. In other words, at the very rearmost end of the screw 12, there is no plane perpendicular to the rotation center line LN1 of the screw 12. Figure 2 Orthogonal planes. At the rear end of the outer peripheral protrusion 50, an outer peripheral protrusion slope 50S and a second outer peripheral protrusion slope 50SS are formed facing the rear end of the outer peripheral protrusion 50.

[0034] The outer peripheral protrusion slope 50S is formed on one of the two sides 50F1 and 50F2 of the outer peripheral protrusion 50 in the circumferential direction of the screw 12. The outer peripheral protrusion slope 50S is inclined in such a way that the width 50W of the outer peripheral protrusion is smaller as it faces the rear end along the circumferential direction of the screw 12.

[0035] The second outer peripheral protrusion 50SS is inclined such that the outer diameter of the screw 12 decreases as it approaches the rear end of the outer peripheral protrusion 50. That is, the second outer peripheral protrusion 50SS is inclined such that the radius R1 of the screw 12 is approximately equal to the distance from the rear end of the outer peripheral protrusion 50 to the rotation center line LN1 of the screw 12. Figure 3A The smaller the tilt, the better.

[0036] A plurality of inner peripheral protrusions 60 are formed on the inner peripheral surface of the through hole 14H of the bushing 14, which extend in the front-rear direction at intervals in the circumferential direction of the through hole 14H. Each of the plurality of inner peripheral protrusions 60 has the same shape. The following description relating to the shape of the inner peripheral protrusion 60 refers only to one of the plurality of inner peripheral protrusions 60. The front end of the inner peripheral protrusion 60 is formed into a pointed shape or a rounded shape. That is, there is no flat surface at the front end of the inner peripheral protrusion 60 of the bushing 14. In other words, at the very front end of the bushing 14, there is no point of contact with the center line LN2 of the through hole 14H of the bushing 14. Figure 2 Orthogonal planes. At the front end of the inner peripheral protrusion 60, an inner peripheral protrusion slope 60S and a second inner peripheral protrusion slope 60SS are formed facing the front end of the inner peripheral protrusion 60.

[0037] An inner circumferential protrusion 60S is formed on one of the two sides 60F1 and 60F2 of the inner circumferential protrusion 60 in the circumferential direction of the through hole 14H. The inner circumferential protrusion 60S is inclined in such a way that the width 60W of the inner circumferential protrusion decreases as it faces the front end along the circumferential direction of the through hole 14H.

[0038] The second inner circumferential protrusion 60SS is inclined such that the diameter of the through hole 14H of the bushing 14 increases as it approaches the front end of the inner circumferential protrusion 60. That is, the second inner circumferential protrusion 60SS is inclined such that the radius R2 of the through hole 14H is approximately equal to the distance from the center line LN2 of the through hole 14H to the front end of the inner circumferential protrusion 60. Figure 3B The larger the tilt, the better.

[0039] In the injection device 10, the following relationship (1) holds. Cs1 in equation (1) is the height 50H of the second peripheral protrusion slope 50SS. Figure 3A (1) Cb1 is the height 60H of the second inner circumferential protrusion slope 60SS. Figure 3B (1) Ls1 is the gap GP1 between the outer peripheral protrusion 50 and the cylinder 20 when the screw 12, which is fitted into the bushing 14, is housed in the cylinder 20. Figure 1 (1) Lb1 is the gap GP2 between the outer periphery of the protrusion 14A of the bushing 14 and the inner periphery of the recess 16A of the bushing fastener 16 when the bushing 14 is fixed to the bushing fastener 16. Figure 1 ).

[0040] Cs1+Cb1>Ls1+Lb1.....(1)

[0041] In addition, the height of the second peripheral protrusion slope 50SS is 50H. Figure 3A ) is the radial length (protrusion distance) of the screw 12 between the most prominent position of the outer peripheral protruding slope 50S and the rear end of the outer peripheral protruding slope 50S. Additionally, the height 60H of the second inner peripheral protruding slope 60SS ( Figure 3B) is the radial length (protrusion distance) of the bushing 14 between the most prominent position of the inner circumferential protrusion slope 60S and the front end of the inner circumferential protrusion slope 60S.

[0042] Figure 4 This is a flowchart illustrating the control process executed by the motor control unit 28 to spline-fit the screw 12 and bushing 14. This control process begins after the bushing 14 moves to a predetermined engagement start position, moving rearward from the rear end face of the screw 12. Furthermore, at the engagement start position, the rotation center line LN1 of the screw 12... Figure 2 The centerline LN2 of the through hole 14H of bushing 14 and bushing 14. Figure 2 As long as equation (1) is satisfied, they can be inconsistent.

[0043] In step S1, the motor control unit 28 moves the bushing 14 toward the screw 12. When the forward movement of the bushing 14 begins, the control process transfers to step S2.

[0044] In step S2, the motor control unit 28 compares the direct torque detected by the detection unit 38 during the forward movement of the bushing 14 with a direct torque threshold. Here, if the direct torque does not exceed the direct torque threshold, the control process remains in step S2. On the other hand, if the direct torque exceeds the direct torque threshold, the control process proceeds to step S3.

[0045] Furthermore, the phenomenon of direct torque exceeding the direct torque threshold occurs when the rear end face of the screw 12, after being splined with the bushing 14, is in contact with the bottom surface of the recess 16A of the bushing fastener 16.

[0046] In step S3, the motor control unit 28 stops the forward movement of the bushing 14 when the direct torque exceeds the direct torque threshold. When the forward movement of the bushing 14 stops, the control process ends.

[0047] Thus, an outer peripheral protrusion slope 50S and a second outer peripheral protrusion slope 50SS are formed on the outer peripheral protrusion 50 of the screw 12, and there is no flat surface at the rear end of the outer peripheral protrusion 50. On the other hand, an inner peripheral protrusion slope 60S and a second inner peripheral protrusion slope 60SS are formed on the inner peripheral protrusion 60 of the bushing 14, and there is no flat surface at the front end of the inner peripheral protrusion 60. As a result, spline engagement can be achieved by the forward movement of the bushing 14 relative to the screw 12 without rotating the bushing 14, thereby improving the efficiency of spline engagement.

[0048] Furthermore, in the injection device 10, the relationship in equation (1) above holds true. Thus, it is possible to perform spline engagement by the forward movement of the bushing 14 relative to the screw 12 without rotating the bushing 14, while taking into account the cylinder 20 that houses the screw 12 and the bushing fastener 16 that fixes the bushing 14.

[0049] Furthermore, the injection device 10 has a motor control unit 28 that controls the direct-drive motor 24. The motor control unit 28 advances the bushing 14 from a position away from the screw 12 and stops the bushing 14 when the direct-drive torque exceeds the direct-drive torque threshold. As a result, spline engagement can be automated, thereby reducing the time deviation required for spline engagement due to operator skill level.

[0050] [Variation Example]

[0051] The above-described implementation methods can also be modified as follows.

[0052] (Variation Example 1)

[0053] Figure 5 This is a diagram showing the screw 12 and bushing 14 in modified example 1. Figure 5 In this variation, structures identical to those described in the embodiments are labeled with the same symbols. Furthermore, in this variation, descriptions that are repeated in the embodiments are omitted.

[0054] In this modified example, the outer peripheral protrusions 50S of the outer peripheral protrusions 50 are formed on the two circumferential sides 50F1 and 50F2 of the screw 12. Similarly, the inner peripheral protrusions 60S of the inner peripheral protrusions 60 are formed on the two circumferential sides 60F1 and 60F2 of the through hole 14H. Even with this configuration, as in the previous embodiment, spline engagement can be achieved through the forward movement of the bushing 14 relative to the screw 12 without rotating the bushing 14.

[0055] (Variation Example 2)

[0056] The second peripheral protruding inclined surface 50SS can also be formed between the peripheral protrusions 50, in addition to the peripheral protrusions 50, as in Modified Example 1. Thus, even if the center line LN2 of the through hole 14H of the bushing 14 is offset radially from the rotation center line LN1 of the screw 12, the bushing 14 can still move towards the screw 12 to perform spline engagement.

[0057] (Variation Example 3)

[0058] The rear end of the peripheral protrusion 50 can be located on the same plane as the rear end face of the screw 12, or it can be located in a position forward of the rear end face of the screw 12. That is, in the embodiment, the rear end of the peripheral protrusion 50 can be located in a position forward of the rear end face of the screw 12. In addition, in Modification 1, the rear end of the peripheral protrusion 50 can also be located on the same plane as the rear end face of the screw 12.

[0059] The front end of the inner peripheral protrusion 60 can be located on the same plane as the front end face of the bushing 14, or it can be located further back than the front end face of the bushing 14. That is, in the embodiment, the front end of the inner peripheral protrusion 60 can be located further back than the front end face of the bushing 14. In addition, in Modification 1, the front end of the inner peripheral protrusion 60 can also be located on the same plane as the front end face of the bushing 14.

[0060] (Variation Example 4)

[0061] The above-described implementation methods and variations can be combined arbitrarily without causing contradictions.

[0062] The above can be summarized as follows.

[0063] The present invention is an injection device (10) comprising: a screw (12) arranged along a front-rear direction, wherein the front direction for injecting injection resin is a forward direction and a rear direction opposite to the forward direction; and a bushing (14) formed to engage with the spline of the screw.

[0064] The screw has a plurality of peripheral protrusions (50) formed on the outer peripheral surface of the rear end side of the screw, and extending at intervals along the front-rear direction in the circumferential direction of the screw.

[0065] The plurality of peripheral protrusions are respectively formed with: a peripheral protrusion bevel (50S), which is inclined such that the width (50W) of the peripheral protrusion along the circumference of the screw decreases as it approaches the rear end of the peripheral protrusion; and a second peripheral protrusion bevel (50SS), which is inclined such that the outer diameter of the screw decreases as it approaches the rear end of the peripheral protrusion.

[0066] The bushing has: a through hole (14H) extending in the front-rear direction; and a plurality of inner peripheral protrusions (60) formed on the inner peripheral surface of the through hole and extending at intervals along the front-rear direction in the circumferential direction of the through hole.

[0067] The plurality of inner peripheral protrusions are respectively formed with: an inner peripheral protrusion bevel (60S), which is inclined such that the width (60W) of the inner peripheral protrusion along the circumference of the through hole decreases as it approaches the front end of the inner peripheral protrusion; and a second inner peripheral protrusion bevel (60SS), which is inclined such that the inner diameter of the bushing increases as it approaches the front end of the inner peripheral protrusion.

[0068] There is no plane at the rear end of each of the plurality of peripheral protrusions and at the front end of each of the plurality of inner peripheral protrusions.

[0069] Therefore, spline engagement can be achieved without rotating the bushing, but rather through the forward movement of the bushing relative to the screw. As a result, the efficiency of spline engagement can be improved.

[0070] Alternatively, the peripheral protrusion bevel may be formed on one of the two circumferential sides (50F1, 50F2) of the screw on the rear end side of each of the plurality of peripheral protrusions.

[0071] The inner peripheral protrusion slope is formed on one of the two circumferential sides (60F1, 60F2) of the through hole at the front end of each of the plurality of inner peripheral protrusions.

[0072] Therefore, spline engagement can be achieved without rotating the bushing, but rather through the forward movement of the bushing relative to the screw.

[0073] Alternatively, the peripheral protruding inclined surface may be formed on each of the two circumferential sides of the screw on the rear end side of each of the plurality of peripheral protrusions.

[0074] The inner circumferential protrusion bevel is formed on each of the two circumferential sides of the through hole at the front end of each of the plurality of inner circumferential protrusions.

[0075] Therefore, spline engagement can be achieved without rotating the bushing, but rather through the forward movement of the bushing relative to the screw.

[0076] Alternatively, the bushing may be provided with a protrusion (14A) that protrudes from the rear end face of the bushing.

[0077] The injection device has:

[0078] A bushing fastener (16) having a recess (16A) for receiving the protrusion, and securing the bushing that receives the protrusion in the recess; and

[0079] Cylinder (20), which houses the screw,

[0080] When the height (50H) of the second outer peripheral protrusion slope is set to Cs1, the height (60H) of the second inner peripheral protrusion slope is set to Cb1, the gap (GP1) between the outer peripheral protrusion and the cylinder when the screw fitted into the bushing is housed in the cylinder is set to Ls1, and the gap (GP2) between the outer periphery of the convex portion and the inner periphery of the concave portion when the bushing is fixed to the bushing fastening portion is set to Lb1,

[0081] The relationship Cs1+Cb1>Ls1+Lb1 holds true.

[0082] Therefore, it is possible to achieve spline engagement by means of the forward movement of the bushing relative to the screw, without rotating the bushing, while simultaneously considering the cylinder that houses the screw and the bushing fastener that fixes the bushing.

[0083] Alternatively, the injection device may have:

[0084] A direct-drive motor (24) causes the bushing to move forward and backward relative to the screw in the front-back direction;

[0085] The detection unit (38) detects the direct torque of the direct-drive motor; and

[0086] The motor control unit (28) controls the direct motor to advance the bushing from a position away from the screw and to stop the bushing when the direct torque exceeds the direct torque threshold.

[0087] This enables the automation of spline engagement. Consequently, it reduces the time deviation in spline engagement caused by operator skill level.

Claims

1. An injection device (10) comprising: a screw (12) arranged along a front-rear direction, wherein the front direction refers to the direction in which a resin for injection is injected and the opposite rear direction; a bushing (14) formed to engage with the spline of the screw, characterized in that, The screw has a plurality of peripheral protrusions (50) formed on the outer peripheral surface of the rear end side of the screw, and extending at intervals along the front-rear direction in the circumferential direction of the screw. The plurality of peripheral protrusions are respectively formed with: a peripheral protrusion bevel (50S), which is inclined such that the width (50W) of the peripheral protrusion along the circumference of the screw decreases as it approaches the rear end of the peripheral protrusion; and a second peripheral protrusion bevel (50SS), which is inclined such that the outer diameter of the screw decreases as it approaches the rear end of the peripheral protrusion. The bushing has: a through hole (14H) extending in the front-rear direction; and a plurality of inner peripheral protrusions (60) formed on the inner peripheral surface of the through hole and extending at intervals along the front-rear direction in the circumferential direction of the through hole. The plurality of inner peripheral protrusions are respectively formed with: an inner peripheral protrusion bevel (60S), which is inclined such that the width (60W) of the inner peripheral protrusion along the circumference of the through hole decreases as it approaches the front end of the inner peripheral protrusion; and a second inner peripheral protrusion bevel (60SS), which is inclined such that the inner diameter of the bushing increases as it approaches the front end of the inner peripheral protrusion. Each of the plurality of peripheral protrusions has no plane or edge formed by the peripheral protrusion at its rear end, and each of the plurality of inner peripheral protrusions has no plane or edge formed by the inner peripheral protrusion at its front end. The rear end of the second outer peripheral protruding slope reaches the position of the rear end of the outer peripheral protruding slope, and the front end of the second inner peripheral protruding slope reaches the position of the front end of the inner peripheral protruding slope.

2. The injection device according to claim 1, characterized in that, The peripheral protrusion bevel is formed on one of the two circumferential sides (50F1, 50F2) of the screw on the rear end side of each of the plurality of peripheral protrusions. The inner peripheral protrusion slope is formed on one of the two circumferential sides (60F1, 60F2) of the through hole at the front end of each of the plurality of inner peripheral protrusions.

3. The injection device according to claim 1, characterized in that, The peripheral protruding bevel is formed on each of the two circumferential sides of the screw on the rear end side of each of the plurality of peripheral protrusions. The inner circumferential protrusion bevel is formed on each of the two circumferential sides of the through hole at the front end of each of the plurality of inner circumferential protrusions.

4. The injection device according to any one of claims 1 to 3, characterized in that, The bushing is provided with a protrusion (14A) that protrudes from the rear end face of the bushing. The injection device has: A bushing fastener (16) having a recess (16A) for receiving the protrusion, and securing the bushing that receives the protrusion in the recess; and Cylinder (20), which houses the screw, When the height (50H) of the second outer peripheral protrusion slope is set to Cs1, the height (60H) of the second inner peripheral protrusion slope is set to Cb1, the gap (GP1) between the outer peripheral protrusion and the cylinder when the screw fitted into the bushing is housed in the cylinder is set to Ls1, and the gap (GP2) between the outer periphery of the convex portion and the inner periphery of the concave portion when the bushing is fixed to the bushing fastening portion is set to Lb1, The relationship Cs1+Cb1>Ls1+Lb1 holds true.

5. The injection device according to any one of claims 1 to 3, characterized in that, The injection device has: A direct-drive motor (24) causes the bushing to move forward and backward relative to the screw in the front-back direction; The detection unit (38) detects the direct torque of the direct-drive motor; and The motor control unit (28) controls the direct motor to advance the bushing from a position away from the screw and to stop the bushing when the direct torque exceeds the direct torque threshold.

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