A process for improving the control accuracy of servo presses

Abstract

This invention discloses a process for improving the control accuracy of a servo press, comprising: taking the point where the slider is at its highest position within a circle formed by the crankshaft rotating around its center line as the initial set point; taking the point on the circle at 180° to the initial set point as the bottom dead center; and taking the point where the slider rotates to its final position as the positioning and pressing stop point. When the initial set point rotates to the positioning and pressing stop point, the path traversed by the crankshaft is a minor arc that does not pass through the bottom dead center. A position ruler is installed on the servo press to achieve slider positioning. Precise positioning using the position ruler enables closed-loop position control. This effectively avoids the impact of gear backlash and deformation on workpiece accuracy during full-stroke pressing processes using a gear-structured servo motor. By avoiding the bottom dead center and combining it with closed-loop control using the position ruler, the positioning accuracy of the slider is effectively achieved, thus improving the pressing accuracy, which can be controlled within 0.005mm.

Description

Technical Field

[0001] This invention belongs to the field of servo press technology, specifically relating to a process for improving the control accuracy of servo presses. Background Technology

[0002] A press is a forging and pressing machine driven by a crank-connecting rod or toggle mechanism, cam mechanism, or screw mechanism. It is a machine tool used to process materials under pressure, deforming and fracturing the workpiece to produce parts. A servo press, also known as a servo press fitting machine, is typically driven and controlled by a servo motor. It can achieve closed-loop control of the pressing force and depth throughout the entire pressing process, thus enabling precision pressing with online quality management.

[0003] like Figure 1 As shown, existing servo presses generally include a servo motor, crankshaft, and slide block. The output end of the servo motor has a pinion gear, and the input end of the crankshaft has a large gear. The meshing of the pinion and large gears transmits the output power of the servo motor to the crankshaft, driving its rotation and subsequently moving the slide block up and down to stamp the workpiece, ultimately completing the part processing. Existing servo presses require full-stroke stamping to complete the part processing, passing through the machine tool's bottom dead center (180°), meaning the angle between the positioning pressing point and the starting point is greater than or equal to 180°. This means the rotation angle of the large gear or crankshaft exceeds 180° during operation. The accuracy of this type of servo press is determined by mechanical strength, rigidity, and machining precision, resulting in poor controllability and low accuracy. Current approaches often involve modifying the press, such as adding a tonnage control device or using separate systems to drive the inner and outer slide blocks to improve accuracy. However, these methods are costly. Therefore, it is necessary to optimize the stamping process of existing servo presses. Summary of the Invention

[0004] To address the aforementioned technical problems, the objective of this invention is to provide a process for improving the control accuracy of a servo press.

[0005] The technical solution of this invention is:

[0006] The purpose of this invention is to provide a process for improving the control accuracy of a servo press, comprising: in a circle formed by the crankshaft rotating around its center line, taking the point where the slider is at its highest position on the circle as the starting set point, taking the point on the circle that forms a 180° angle with the starting set point as the bottom dead center, and taking the point on the circle where the slider rotates to the position when pressed into place as the positioning pressing stop point. When the starting set point rotates to the positioning pressing stop point, the trajectory of the crankshaft is formed as a minor arc that does not pass through the bottom dead center. Furthermore, a position ruler is provided on the servo press to realize the positioning of the slider. Position closed-loop control is realized through the precise positioning of the position ruler.

[0007] Preferably, the pressing process is divided into four stages, which are designated as the first stage, the second stage, the third stage, and the fourth stage in sequence. The first stage is the rapid downward section of the slider when the crankshaft rotates at the first angular velocity ω1. The second stage is the deceleration section of the slider when the crankshaft rotates at the second angular velocity ω2. The third stage is the pressing section when the crankshaft rotates at the third angular velocity ω3. The fourth stage is the reverse return section when the crankshaft rotates in the opposite direction to the starting set point at the fourth angular velocity ω4, where ω4 > ω1 > ω2 > ω3. The time for the slider to descend in the first stage is less than the time for the slider to descend in the second stage.

[0008] Preferably, the crankshaft rotation angle during the rapid downward movement of the slider is set to θ1 and the time is t1, the total crankshaft rotation angle at the end of the slider deceleration phase is set to θ2 and the time is t2, the radius of the circle is R, the pressing depth of the workpiece to be pressed is h, 0 < θ1 < 180°, 0 < θ2 < 180°, 0 < θ3 < 180°, and the total crankshaft rotation angle at the end of the slider micro-motion phase is set to θ3, and θ3 can be varied according to the pressing depth of the workpiece to be pressed.

[0009] ω1 and ω2 can be calculated from the angular velocity ω=Δθ / Δt, and θ3 can be calculated from θ2, h and R, where θ3=180°-arccos[cos(180°-θ2)+h / R].

[0010] Preferably, θ1 satisfies the following condition 0 < θ1 < 120°, and θ2 satisfies the following condition 120° < θ2 < 150°.

[0011] Preferably, the crankshaft rotation angle in the first stage is greater than half the sum of the rotation angles in the first, second, and third stages.

[0012] Preferably, the time of the fourth stage is no greater than the time of the first stage or the sum of the times of the first, second and third stages.

[0013] Preferably, after the third stage is completed and before the fourth stage begins, the slider needs to remain for a preset time, which is no more than 2 seconds.

[0014] Preferably, the position ruler is a grating ruler.

[0015] Compared with the prior art, the advantages of the present invention are:

[0016] This invention improves the control precision of a servo press by using a process where the crankshaft presses within half a revolution during the pressing process. Simultaneously, a positioning ruler is installed on the servo press to locate the slider position. Precise positioning using this ruler enables closed-loop position control. This effectively avoids the gear backlash and vibration issues inherent in traditional full-stroke pressing processes (which require passing the bottom dead center) and the deformation effects on workpiece precision during heavy-duty pressing, which are present in gear-driven servo motors. By improving the pressing process by avoiding the bottom dead center and combining it with closed-loop control using the positioning ruler, the positioning precision of the slider is effectively achieved, thus improving the pressing precision. The precision range can be controlled within 0.005mm. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0018] Figure 1 This is a schematic diagram of the control precision process of the servo press according to an embodiment of the present invention (where the left side of the figure is a simplified structural diagram of the servo press, the middle is a schematic diagram of the four stages of the pressing stroke, and the right side is a slider motion curve, where the horizontal axis is the crankshaft rotation angle and the vertical axis is the pressing stroke).

[0019] Figure 2 for Figure 1 A magnified structural diagram of the four stages of the pressing stroke in the crankshaft rotation trajectory.

[0020] The components include: 1. Servo motor; 2. Pinion; 3. Gear; 4. Crankshaft; 5. Connecting rod; 6. Slider; 7. Position ruler. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0022] See Figures 1 to 2 The servo press of this invention, as in embodiments thereof, Figure 1As shown in the left-hand diagram, the system includes a servo motor 1, a crankshaft 4, a slider 6, and a position ruler 7. The servo motor 1 and crankshaft 4 are connected by a gear structure, which includes a meshing pinion 2 and a large gear 3. The pinion 2 is located at the output end of the servo motor 1, and the large gear 3 is located at the input end of the crankshaft 4. The crankshaft 4 and slider 6 are connected by a connecting rod 5. The position ruler 7 is located on one side of the slider 6. The process for controlling the accuracy of the servo press according to this embodiment of the invention is as follows: Figure 1 As shown in the middle diagram, around the crankshaft 4's center line of rotation, that is... Figure 1 In the circle formed by the rotation center line of the large gear 3 shown in the figure, which is the solid circle inside the large dotted circle in the figure, the point in this circle where the slider 6 is at its highest position is... Figure 1 The starting point is A, which is the intersection of the upper end of the vertical diameter of the solid circle shown in the diagram and the circle itself. The point on the solid circle that forms a 180° angle with the starting point is also considered... Figure 1 The intersection point E between the lower end of the vertical diameter of the solid-line circle shown and the circle is the bottom dead center. The point where the slider 6 on the solid-line circle rotates to its final position when pressed is taken as the positioning and pressing stop point, i.e., as shown... Figure 1 As shown in the diagram, when the starting point (i.e., point A) rotates to the positioning and pressing stop point (i.e., point D), the path traversed by crankshaft 4 forms a minor arc that does not pass through the bottom dead center. Figure 1 The arc ABCD shown in the figure. That is to say, the servo press of this embodiment of the invention does not have a traditional full-stroke pressing stroke. Figure 1 The arc ABCDE shown is not pressed within a half-circle, meaning the crankshaft 4 rotates less than the 180° full-stroke pressing angle of a conventional servo press when pressing the workpiece, from the initial set point to the point where the workpiece is just finished. To improve accuracy, a position ruler 7 is installed on the servo press to position the slider 6, achieving closed-loop position control through precise positioning of the position ruler 7. This process effectively avoids the gear backlash and deformation affecting workpiece accuracy in traditional full-stroke pressing processes (which require passing the bottom dead center) using a gear-structured servo motor. By improving the pressing process by avoiding the bottom dead center, combined with closed-loop control of the position ruler, the positioning accuracy of the slider is effectively achieved, thus improving the pressing accuracy. The accuracy range can be controlled within 0.005mm, making it particularly suitable for workpieces sensitive to tonnage and high-precision workpieces such as explosion-proof plates and valves on new energy battery casings.

[0023] According to some preferred embodiments of the present invention, such as Figure 1As shown in the middle figure, the pressing process of the servo press in this embodiment of the invention is divided into four stages, which are sequentially designated as the first stage (i.e., segments A to B in the figure), the second stage (i.e., segments B to C in the figure), the third stage (i.e., segments C to D in the figure), and the fourth stage (i.e., segments D to A in the figure). The first stage is the rapid downward section of the slider when the crankshaft 4 rotates at the first angular velocity ω1. The second stage is the deceleration section of the slider when the crankshaft 4 rotates at the second angular velocity ω2. The third stage is the pressing section when the crankshaft 4 rotates at the third angular velocity ω3. The fourth stage is the reverse return section when the crankshaft 4 rotates in the opposite direction to the starting set point at the fourth angular velocity ω4, where ω4 > ω1 > ω2 > ω3. In the first stage, the rotation angle θ1 of the crankshaft 4 is greater than the rotation angle (θ2-θ1) in the second stage and the rotation angle (θ3-θ2) in the third stage. In the second stage, the rotation angle (θ2-θ1) of the crankshaft 4 is greater than the rotation angle (θ3-θ2) in the third stage. In the first stage, the time t1 for the slider 6 to descend is less than the time t2 for the slider 6 to descend in the second stage. No particular limitations are made regarding the rotational angular velocity of crankshaft 4 in the four stages and the time required for each stage; those skilled in the art can select and design according to actual needs. See Figure 1 The slider motion curve shown in the right-hand figure is a standard cosine curve in the prior art. However, the improved pressing process of this invention does not exceed the bottom dead center of 180°, so the slider motion curve is not a complete cosine curve.

[0024] Preferably, such as Figure 2 As shown, in the first stage of the rapid downward movement of slider 6, the angle of rotation of crankshaft 4 is set to θ1 and the time is t1. In the second stage of the deceleration movement of slider 6, the angle of rotation of crankshaft 4 is set to θ2 and the time is t2. The radius of the circle is R, and the pressing depth of the workpiece to be pressed is h. 0 < θ1 < 180°, 0 < θ2 < 180°, 0 < θ3 < 180°. Let the angle of rotation of crankshaft 4 in the third stage of the micro-motion movement of slider 6 be θ3, and let θ3 be variable according to the pressing depth of the workpiece to be pressed. According to the angular velocity ω = Δθ / Δt, ω1 and ω2 can be calculated respectively. According to θ2, h and R, θ3 can be calculated, where θ3 = 180° - arccos[cos(180° - θ2) + h / R]. In other words, the process parameters for the first, second, and fourth stages are the same for different workpieces. The difference lies in the third stage, where the rotation angle θ3 of the crankshaft 6 is variable and varies according to the pressing depth h of the workpiece. However, regardless of the pressing depth, the rotation angle θ3 of the crankshaft 6 is always less than 180°. In a preferred embodiment, θ1 satisfies the condition 0 < θ1 < 120°, and θ2 satisfies the condition 120° < θ2 < 150°.

[0025] Preferably, the crankshaft rotation angle in the first stage is greater than half the sum of the rotation angles in the first, second, and third stages. That is, θ1 > 1 / 2θ3. This design can further improve efficiency.

[0026] According to some preferred embodiments of the present invention, the position ruler 7 is not described in detail or limited, and can be any commercially available position sensor. For example, in this embodiment, the position ruler 7 is a grating ruler, which has the characteristics of a large detection range, high detection accuracy, and fast response speed. The principle of the closed-loop control of the position ruler 7 in this embodiment is to compare the feedback from the actual position of the motor encoder (not shown) and the grating ruler, and achieve closed-loop positioning control through deviation compensation. Due to errors such as gaps in the mechanical structure, there is a deviation between the feedback value of the encoder and the feedback value of the position ruler. The actual target position is based on the grating ruler, and closed-loop positioning control is achieved through deviation compensation. The specific method and principle of deviation compensation are not described or limited, but are existing conventional deviation compensation methods that are easily known and implemented by those skilled in the art.

[0027] For example, in embodiments of the present invention, such as Figure 2As shown, in the first stage, the rotation angle θ1 of crankshaft 4 ranges from 0 to 120 degrees (here, θ1 = 120°), meaning the central angle corresponding to the arc length between points A and B is 120°. The downward movement time of slider 6 in the first stage is set to 0.5s (i.e., t1 = 0.5s). Therefore, the angular velocity ω1 of crankshaft 4 in the first stage can be calculated as 4.18 rad / s using the angular velocity calculation formula. In the second stage, the rotation angle of crankshaft 4 ranges from 120 to 150 degrees (here, θ2 = 150°), meaning the central angle corresponding to the arc length between points A and C is 150°. The downward movement time of slider 6 in the second stage is set to 2s (i.e., t2 = 2s). Therefore, the angular velocity ω2 of crankshaft 4 in the second stage can be calculated as 0.26 rad / s using the angular velocity calculation formula. It can be seen that ω2 < ω1, which is consistent with the above description. Let the radius of the crankshaft, i.e., the radius R of the solid circle in the above figure, be 30mm. In the first stage, the vertical distance H1 from the starting point of crankshaft 4 (i.e., point B) to the bottom dead center is 15mm, which means the downward height of slider 6 is 15mm. The vertical distance H2 from point C to the bottom dead center is 4.019mm. When crankshaft 4 rotates to position C, the pressing surface of slider 6 is close to (can be understood as just contacting or having only a negligible gap) pressing the workpiece surface. In the third stage, the workpiece to be pressed is set... The thickness before pressing is 5mm, and the required pressing depth is 2mm (i.e., h=2mm). Therefore, the vertical distance H3 from the midpoint D of the circle to the bottom dead center is calculated to be 2.019mm. Using the formula θ3=180°-arccos[cos(180°-θ2)+h / R], the rotation angle θ3 of the crankshaft 4 in the third stage can be calculated. The calculated θ3 is in radians, which, when converted to angles, is 159° < 180°, consistent with the above description. It should be noted that the angular velocity ω3 of the crankshaft 4 in the third stage is relatively small, and the slider 6 moves at a small speed. The specific angular velocity ω3 can be selected and designed according to actual requirements. For example, in this embodiment of the invention, ω3 is 0.15 rad / s, which is less than ω2 and ω1. Under the closed-loop control of the position ruler 7, the slider 6 moves downward by 2 mm, corresponding to a position on the circle where it moves downward by 2 mm from point C to a position 2.019 mm vertically from the bottom dead center, i.e., point D on the circle (the positioning and pressing stop point), where pressing stops. Point D is the set point for pressing to be in place. It should be noted that when the positioning and pressing stop point is reached, the slider 6 stops moving, and the crankshaft 4 also stops moving at point D. The dwell time is not limited and depends on the mold used, but generally does not exceed 2 seconds. The purpose of stopping at point D is to release the pressing stress, ensure that the pressed and formed parts meet the product requirements, improve the precision and uniformity of the products, and improve the product yield.The fourth stage is the reverse fast return stage. The time t4 of this stage is generally no greater than the time t1 of the first stage or the sum of the times of the previous three stages (t1+t2+t3). For example, in this embodiment of the invention, the time of the fourth stage is 0.5s. The purpose of this setting is to improve production efficiency and return to the starting setpoint at a fast speed.

[0028] The specified directions in this specific embodiment are merely for the purpose of facilitating the description of the positional relationships and mutual cooperation between the components. The above description is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A process for improving the control accuracy of a servo press, characterized in that, include: In the circle formed by the crankshaft around its rotation center line, the point where the slider is at its highest position on the circle is taken as the starting set point, the point on the circle that is 180° to the starting set point is taken as the bottom dead center, and the point on the circle where the slider rotates to the position when pressed into place is taken as the positioning pressing stop point. When the starting set point rotates to the positioning pressing stop point, the trajectory of the crankshaft is formed as a minor arc that does not pass through the bottom dead center. Furthermore, a position ruler is provided on the servo press to realize the slider position positioning. Position closed-loop control is realized through the precise positioning of the position ruler. The pressing process is divided into four stages, which are designated as the first stage, the second stage, the third stage, and the fourth stage in sequence. The first stage is the rapid downward section of the slider when the crankshaft rotates at the first angular velocity ω1. The second stage is the deceleration section of the slider when the crankshaft rotates at the second angular velocity ω2. The third stage is the pressing section when the crankshaft rotates at the third angular velocity ω3. The fourth stage is the reverse return section when the crankshaft rotates in the opposite direction at the fourth angular velocity ω4 to the starting set point, where ω4 > ω1 > ω2 > ω3. The time for the slider to descend in the first stage is less than the time for the slider to descend in the second stage. After the third stage is completed and before the fourth stage begins, the slider needs to remain for a preset time, which is no more than 2 seconds. Set the crankshaft rotation angle during the rapid downward movement of the slider to θ1 and the time to t1, the total crankshaft rotation angle at the end of the slider deceleration phase to θ2 and the time to t2, the radius of the circle to R, and the pressing depth of the workpiece to be pressed to h, where 0 < θ1 < 120°, 120° < θ2 < 150°, and 0 < θ3 < 180°. Let the total crankshaft rotation angle at the end of the slider micro-motion phase be θ3, and let θ3 be variable according to the pressing depth of the workpiece to be pressed. ω1 and ω2 can be calculated from the angular velocity ω=Δθ / Δt, and θ3 can be calculated from θ2, h and R, where θ3=180°-arccos[cos(180°-θ2)+h / R]; In the first stage, the crankshaft rotates at an angle greater than half the sum of the rotation angles in the first, second, and third stages. The duration of the fourth stage shall not exceed the duration of the first stage or the sum of the durations of the first, second, and third stages.

2. The process for improving the control accuracy of a servo press according to claim 1, characterized in that, The position ruler is a grating ruler.

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