Manipulator and injection molding machine cooperative motion control method

Abstract

The invention relates to the technical field of manipulator cooperative control, in particular to a manipulator and injection molding machine cooperative motion control method. The method comprises the steps that the real-time position of a movable template in the mold opening process of the injection molding machine is obtained; generating a following target point based on the real-time position and a preset grabbing point offset; acquiring a fluctuation index; a dynamic safety margin is constructed, the following target point is corrected in the direction away from the movable template, and a corrected synchronous target point is obtained; and a manipulator is controlled to track the synchronous target point to enter a mold cavity, and the product is grabbed after the synchronous target point reaches a grabbing position. According to the scheme, cooperative movement of the manipulator and the injection molding machine can be efficiently achieved.

Description

Technical Field

[0001] This invention relates to the field of robotic arm collaborative control technology. More specifically, this invention relates to a method for collaborative motion control of a robotic arm and an injection molding machine. Background Technology

[0002] In modern injection molding production lines, automated part handling by robotic arms is a key element in achieving unmanned production. Typically, the robotic arm controller and the injection molding machine controller communicate via a standard industrial interface to coordinate their actions. The core technology involves using a pre-programmed logic sequence to control the robotic arm to enter the mold cavity after the injection molding machine has opened, grab the finished product, and then exit, allowing the injection molding machine to proceed with the next mold closing and injection process.

[0003] However, existing collaborative control methods have significant limitations. To ensure absolute safety, a serial interlocking logic based on discrete I / O signals is commonly used. Under this logic, the robot arm must strictly wait for the injection molding machine controller to send a "mold opening complete and in position" signal before it can begin its movement into the mold cavity. This intermittent, step-by-step control method of "mold opening first, part removal later" results in the robot arm being completely stationary during the entire mold opening process. This waiting window occupies a portion of each production cycle. In mass production scenarios that pursue high efficiency and fast cycle time, this accumulated waste of time greatly limits the potential for compressing the overall production cycle time, thus affecting the final production efficiency.

[0004] Therefore, how to safely eliminate or shorten this waiting time and achieve smooth synchronization of the robot arm and injection molding machine's movements is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to propose a method for coordinated motion control between a robotic arm and an injection molding machine, in order to solve the problem in the prior art that the robotic arm needs to wait time when picking up parts from the mold and cannot coordinate with the movement of the injection molding machine; to this end, this invention provides a solution in one aspect.

[0006] This invention provides a method for coordinated motion control of a robotic arm and an injection molding machine, comprising: Obtain the real-time position of the moving mold plate during the mold opening process of the injection molding machine; Based on the real-time location and the preset capture point offset, a follow target point is generated; The volatility index is obtained, which is positively correlated with the standard deviation of the instantaneous acceleration of the moving template within a set time window, and positively correlated with the deviation between the moving template trajectory and the historical reference trajectory under the current mold opening cycle. A dynamic safety margin is constructed, which is positively correlated with the volatility index; The following target point is corrected along the direction away from the moving template to obtain the corrected synchronization target point; The robotic arm is controlled to track the synchronous target point and enter the mold cavity, and then grabs the product after reaching the gripping position.

[0007] Optionally, the volatility index includes an instantaneous stationarity index, and the instantaneous stationarity index is calculated using the following method: Collect multiple instantaneous accelerations within a set time window; Calculate the standard deviation of multiple instantaneous accelerations, and use the ratio of the standard deviation to the calibrated maximum normal mold opening acceleration as an instantaneous stationarity index. Optionally, the fluctuation index includes a position deviation index, and the calculation method of the position deviation index includes: Obtain the absolute value of the deviation between the moving mold trajectory and the historical reference trajectory in the current mold opening cycle; The ratio of the absolute value of the deviation to the set deviation threshold is used as the position deviation index.

[0008] Optionally, the historical reference trajectory is at least one of the following: The actual trajectory of the moving template from the previous production cycle; Alternatively, the average trajectory of the actual trajectories of the dynamic template over the most recent N production cycles.

[0009] Optionally, the dynamic safety margin is the sum of the basic safety margin, the environmental risk margin, and the lateral axis dynamic braking distance. The basic safety margin includes the maximum braking distance of the manipulator and a fixed safety margin. The environmental risk margin is positively correlated with the fluctuation index. The lateral axis dynamic braking distance is positively correlated with the square of the lateral axis velocity of the manipulator.

[0010] Optionally, the method for calculating the environmental risk margin is as follows: ; in, For environmental risk margin; The linear gain coefficient; For nonlinear gain coefficients; It is a volatility index; This is the set stability threshold.

[0011] Optionally, obtaining the instantaneous acceleration includes: The instantaneous velocity is obtained by performing a first-order difference on the real-time position; An estimated acceleration is obtained by applying a Kalman filter to the instantaneous velocity, and this estimated acceleration is used as the instantaneous acceleration.

[0012] Optionally, the location of the synchronization target point for: ; in, for Dynamic safety margin at any time Let be the unit direction vector of the robot arm approaching the mold, pointing in the direction away from the moving mold plate. for Constantly follow the location of the target point.

[0013] Optionally, it further includes: setting a dynamic speed limit for the lateral axis of the robot; the dynamic speed limit is positively correlated with the set maximum speed and negatively correlated with the fluctuation index.

[0014] Optionally, it also includes: Real-time monitoring of the actual distance between the robot's end effector and the surface of the moving template; When the actual distance is less than the set ratio of the dynamic safety margin, the safety protection mechanism is triggered, and the robot arm is controlled to retreat urgently in the direction away from the moving template.

[0015] The beneficial effects of this invention are as follows: The method of this invention achieves synchronous follow-up entry of the robot arm during the injection molding process by sensing the motion state of the injection molding machine's motorized mold in real time, dynamically adjusting the safety strategy, and generating a continuously changing robot target trajectory, thereby eliminating waiting time. Attached Figure Description

[0016] Figure 1 This schematically illustrates a flowchart of the steps of a method for controlling the coordinated motion of a robotic arm and an injection molding machine in this embodiment. Figure 2 The schematic diagram illustrates the coordinated motion control trajectory of the robotic arm and the injection molding machine in this embodiment. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0018] Taking a three-axis or five-axis servo robot used in an injection molding production line as an example, this invention introduces a method for coordinated motion control between a robot and an injection molding machine. This method aims to solve the problem in the prior art where, when a robot follows the mold opening action of an injection molding machine to pick up parts, the mold opening trajectory becomes unstable due to hydraulic fluctuations or mechanical vibrations of the injection molding machine, leading to collision risks or forced increases in waiting time and reduced efficiency.

[0019] It should be noted that in the method of the present invention, the feed axis of the robot arm that is parallel to the mold opening direction of the injection molding machine (usually referred to as the transverse axis / main axis / mold entry and exit axis) is the main controlled axis, and the other axes (vertical axis, ejection axis, etc.) are only used for auxiliary interpolation.

[0020] like Figure 1 As shown in this embodiment, a method for coordinated motion control of a robotic arm and an injection molding machine includes the following steps: Step S1: Obtain the real-time position of the moving mold plate during the injection molding machine's mold opening process.

[0021] In this embodiment, the real-time position data of the moving mold is obtained by a grating ruler or a high-precision wire encoder installed on the moving mold of the injection molding machine.

[0022] For example, at the instant the injection molding machine begins to perform the mold opening action, the control system continuously acquires the real-time position of the moving mold in the world coordinate system at a preset high sampling frequency through a real-time data link with the moving mold position sensor (such as a high-precision grating ruler or servo motor encoder). .

[0023] The preset high sampling frequency mentioned above can be 1ms.

[0024] Step S2, Construction and calculation of the volatility index.

[0025] To evaluate the smoothness and predictability of the mold opening motion of an injection molding machine, it is necessary to construct a characteristic index that can quantify the motion stability of the moving mold plate, namely the fluctuation index. In this embodiment, the process of obtaining the fluctuation index is as follows: Step S21: Calculate the instantaneous stationarity index.

[0026] Because irregular jitter or sudden speed changes during mold opening increase the risk of coordinated motion, an ideal, stable motion should have a constant rate of change of velocity (i.e., acceleration) or a smooth change, while drastic fluctuations in acceleration indicate an unstable motion state. Therefore, this embodiment needs to obtain instantaneous stability indicators.

[0027] Specifically, the process of obtaining instantaneous stationarity indicators includes: First, acquire multiple instantaneous accelerations within a set time window.

[0028] In one embodiment, the process of acquiring each instantaneous acceleration is as follows: the real-time position is sampled and the instantaneous velocity observation value is obtained by performing a first-order difference; and the instantaneous velocity observation value is filtered using a Kalman filter, and the smoothed estimated acceleration is taken as the instantaneous acceleration.

[0029] In this embodiment, the time window is set to a range of 0.1 to 0.3 seconds.

[0030] The above scheme aims to accurately capture minute changes in the motion state of the moving template. Instead of directly obtaining acceleration by second-order difference of position, it introduces a Kalman filter for state estimation to eliminate the interference of sensor noise on subsequent fluctuation calculations.

[0031] Since the Kalman filter is an existing technology, it will not be discussed further here.

[0032] Secondly, the standard deviation of multiple instantaneous accelerations is calculated, and the ratio of the standard deviation to the calibrated maximum normal mold opening acceleration is used as the instantaneous stability index.

[0033] Specifically, instantaneous stationarity index for: ; in, To set the standard deviation corresponding to the time window, This refers to the calibrated maximum normal mold opening acceleration of the injection molding machine under ideal operating conditions at full speed. Its value typically ranges from 8 to 15 m / s². 2 .

[0034] The above ratio conversion process eliminates the influence of different dimensions of acceleration measurement for injection molding machines of different tonnages.

[0035] When the hydraulic system of the injection molding machine is stable and the mold opening motion is smooth, the instantaneous acceleration at each moment is close to each other, so the standard deviation tends to 0 and the motion stability index is small. Conversely, if there are sudden speed changes or jitters in the mold opening motion, the instantaneous acceleration will fluctuate violently, resulting in a significant increase in the motion stability index, which directly reflects the increased unpredictability risk of the motion state.

[0036] Step S22: Calculate the position deviation index.

[0037] Since injection molding machines operate cyclically, if we only focus on the data at the current moment and ignore the prediction of historical data from the previous mold, it is difficult to detect that the injection molding machine may sometimes move slowly but incorrectly, such as speed drift caused by changes in oil temperature (when the machine is cold-started, the hydraulic oil viscosity is high, and the mold opening speed may be slower overall) and valve response lag (although the mold opening action is smooth (the acceleration is very small), the start-up time is tens of milliseconds later than usual).

[0038] Therefore, if only acceleration is considered, these situations appear stable, and the robotic arm might misjudge safety and continue to approach, resulting in a collision due to positional deviation. However, by introducing historical trajectory comparison, it can identify situations where the movement is stable but the position is incorrect, thus forcibly maintaining a safe distance. Simultaneously, it can compensate for the blind spot of relying solely on instantaneous acceleration for risk assessment, elevating the control strategy from passive reaction to proactive prediction. Therefore, this embodiment also requires the calculation of positional deviation.

[0039] Specifically, the calculation process for the positional deviation is as follows: Obtain the absolute value of the difference between the actual trajectory of the moving template and the historical reference trajectory at each moment during the current mold opening cycle, and use the ratio of the absolute value of the difference to the set reference deviation threshold as the corrected position deviation.

[0040] Among them, positional deviation for: ; In the formula, The set reference deviation threshold, This is the absolute value of the difference between the trajectory value of the moving template at time t during the current mold opening cycle and the historical trajectory value of the moving template at time t in the historical reference trajectory. The set reference deviation threshold is not zero.

[0041] In one embodiment, historical reference trajectory Select as the most recent The average trajectory of the moving mold's historical actual trajectory over a historical production cycle. Alternatively, the historical actual trajectory of the moving mold's historical actual trajectory from a previous historical production cycle can be selected.

[0042] The above method utilizes the average trajectory of multiple historical production cycles to effectively filter out occasional interference and obtain the standard mold opening curve for the mold.

[0043] The value of N can be 10; of course, as other implementation methods, it can also be determined according to the actual situation.

[0044] The introduction of periodic memory analysis can identify incorrect positioning and thus force a safe distance to be maintained.

[0045] Step S23: Based on the instantaneous stability index and the positional deviation index, the volatility index is obtained.

[0046] In this embodiment, the instantaneous stability index and the position deviation index are combined into a volatility index. .

[0047] Specifically, a weighted summation method is used: ; in, and These are the weighting coefficients, and .

[0048] In this embodiment, considering that sudden acceleration changes are more sensitive to collision risk warnings, it is preferable to set... .

[0049] Step S3: Build dynamic safety margins.

[0050] The core of this embodiment lies in changing the original fixed safety distance limit and constructing a safety envelope that dynamically changes with environmental risks.

[0051] Among them, dynamic safety margin Based on basic safety margin Environmental risk margin and lateral axis dynamic braking distance It consists of three parts, as detailed below: ; Among them, basic safety margin This includes the maximum braking distance of the robotic arm at the current speed and a fixed safety margin (e.g., 5mm).

[0052] Lateral axis dynamic braking distance Considering that the faster the robot arm moves laterally (in the direction of entering the mold cavity), the greater the braking buffer required.

[0053] Therefore, it is positively correlated with the square of the instantaneous velocity of the robot's lateral axis.

[0054] Specifically, the lateral axis dynamic braking distance for: ; The coefficient is determined by the measured maximum deceleration along the transverse axis. The instantaneous velocity at time t during the current mold opening cycle.

[0055] Lateral axis dynamic braking distance It is the dynamic braking distance of the robotic arm itself as its speed changes, which complies with the standard practice for industrial robot safety functions (ISO / TS 15066). Among them, environmental risk margin The calculation formula is: ; in, For environmental risk margin; The linear gain coefficient has a preferred range of [value missing]. ; The nonlinear gain coefficient has a preferred range of [value missing]. ; It is a volatility index; This is the set stability threshold.

[0056] In the above formula, when the volatility index Below the stability threshold At that time, there is only a linearly increasing safety margin to ensure normal production efficiency; once the injection molding machine vibrates violently, causing... Exceed The introduction of nonlinear terms (square terms) causes the safety margin to increase dramatically in a parabolic manner, forcing the robot arm to move away from the moving template quickly, thereby ensuring physical safety under extremely unstable working conditions.

[0057] In this embodiment, when calculating the dynamic safety margin, the larger the environmental risk margin, the more unstable the motion of the moving template is and the higher the potential collision risk. Through the amplification effect of the coefficient, the dynamic safety margin is increased accordingly, thereby reserving more reaction and braking distance for the robot arm in space. When the motion of the moving template is very smooth, the environmental risk margin approaches zero, and the dynamic safety margin falls back to the basic safety value.

[0058] Step S4: Based on the dynamic safety margin, the target point is corrected to achieve coordinated control between the robot and the injection molding machine.

[0059] In this embodiment, after obtaining the real-time position of the moving template, it does not follow it directly, but rather corrects the real-time position. The specific process is as follows: First, based on the current real-time position of the dynamic template, and based on the offset between the current real-time position and the preset capture point, a follow target point is generated.

[0060] Specifically, the target point is located at a fixed relative position of the injection molded part within the mold, and the current real-time position of the mold follows the movement. Let's exercise together.

[0061] Its expression is ,in, It is a pre-calibrated offset vector from the driven template reference point to the injection part gripping point.

[0062] When the offset is 0, the target point coincides with the real-time position. See details below. Figure 2 .

[0063] Secondly, the following target point is corrected along the direction away from the moving template (i.e., the negative Z-axis direction) to obtain the synchronization target point.

[0064] In this embodiment, it must be ensured that the closest distance between the end effector of the robot and the surface of the moving template at any time is not less than the dynamic safety margin.

[0065] Therefore, synchronize target point for: ; in, for Dynamic safety margin at any time This is the unit direction vector for the robot arm to approach the mold, pointing in the direction away from the moving mold.

[0066] The above embodiments are based on following the target point. Based on this, a distance was "pushed back" in the direction away from the mold, and the magnitude of this distance is the currently calculated dynamic safety margin.

[0067] When the moving template is unstable, the dynamic safety margin increases, leading to a decrease in the synchronization target point. As the robot is pushed further away, its following movements will naturally become more conservative (decelerating or maintaining a greater distance); when the moving template moves smoothly, the dynamic safety margin decreases, affecting the synchronization target point. By getting closer to the target point, the robotic arm can follow more actively and closely, thereby minimizing the entry time.

[0068] The aforementioned unit direction vector is a vector pointing from the robot's TCP (tool center point) to the nearest feature point of the moving template through real-time calculation; whereby the nearest feature point is obtained in real-time through the point cloud of the moving template or pre-stored convex hull geometry.

[0069] In this embodiment, the continuously generated sequence of real-time synchronized target points and the upper limit of the dynamic speed of the lateral axis are used as inputs and fed into the path planner and the underlying servo controller of the robot arm to drive the lateral axis and other axes to complete synchronized following motion, so as to control the robot arm's end effector to track and correct the synchronized target points into the mold cavity. Specifically, it can be based on Figure 2 The robot arm and the injection molding machine work together to control the trajectory, so as to control the robot arm's end effector to track and correct the synchronous target point and enter the mold cavity.

[0070] The controller described above uses a high-speed closed-loop control algorithm (such as model predictive control or feedforward + PID control) to calculate the speed and torque required by each joint of the manipulator in real time, driving the manipulator to accurately and smoothly track the synchronous target point of the dynamic change.

[0071] The aforementioned model predictive control or feedforward + PID control can specifically be model predictive control (MPC) with feedforward or iRDynamics-like algorithms.

[0072] The above-mentioned upper limit of dynamic speed of the horizontal axis and the set maximum speed Positive correlation with volatility index It shows a negative correlation.

[0073] That is, when large fluctuations in the operation of the injection molding machine are detected ( When the speed is high, the robotic arm not only moves further away (increased margin), but also moves slower (lower speed limit), achieving double protection.

[0074] In addition, during the coordinated motion, the actual distance between the robot's end effector and the moving template surface is monitored in real time. ;when Time (of which) To set a ratio, for example This triggers a safety protection mechanism, controlling the robotic arm to retreat urgently in a direction away from the moving template to prevent collisions caused by prediction errors.

[0075] Through the above steps, the robotic arm no longer passively waits for the mold opening completion signal, but starts synchronously at the initial stage of the injection molding machine's mold opening. Its movement speed and relative position are dynamically and adaptively adjusted in real time according to the actual smoothness of the injection molding machine's movement. Finally, under the premise of ensuring safety, it reaches the part removal position the instant the mold opens to the correct position in a "zero-wait" manner.

[0076] The present invention constructs a dynamic safety margin model that includes both linear and nonlinear responses by calculating acceleration fluctuations and trajectory deviations in real time. When the injection molding machine is running smoothly, the safety margin narrows, the robot closely follows, and the part removal cycle is significantly shortened; when the injection molding machine experiences hydraulic shock or guide rail jamming, causing abnormal movement, the nonlinear safety margin expands instantaneously, causing the robot to actively retreat, effectively resolving the contradiction between pursuing high efficiency and ensuring safety.

[0077] In the description of this specification, "multiple" means at least two, such as two, three or more, etc., unless otherwise expressly and specifically defined.

[0078] While various embodiments of the invention have been shown and described in this specification, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and essence of the invention.

Claims

1. A method for controlling the coordinated motion of a robotic arm and an injection molding machine, characterized in that, include: Obtain the real-time position of the moving mold plate during the mold opening process of the injection molding machine; Based on the real-time location and the preset capture point offset, a follow target point is generated; The volatility index is obtained, which is positively correlated with the standard deviation of the instantaneous acceleration of the moving template within a set time window, and positively correlated with the deviation between the moving template trajectory and the historical reference trajectory under the current mold opening cycle. A dynamic safety margin is constructed, which is positively correlated with the volatility index; The following target point is corrected along the direction away from the moving template to obtain the corrected synchronization target point; The robotic arm is controlled to track the synchronous target point and enter the mold cavity, and then grabs the product after reaching the gripping position.

2. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 1, characterized in that, The volatility index includes an instantaneous stationarity index, and the calculation method for the instantaneous stationarity index includes: Collect multiple instantaneous accelerations within a set time window; Calculate the standard deviation of multiple instantaneous accelerations, and use the ratio of the standard deviation to the calibrated maximum normal mold opening acceleration as an instantaneous stability index.

3. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 1, characterized in that, The volatility index includes a position deviation indicator, which is calculated using the following methods: Obtain the absolute value of the deviation between the moving mold trajectory and the historical reference trajectory in the current mold opening cycle; The ratio of the absolute value of the deviation to the set deviation threshold is used as the position deviation index.

4. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 1, characterized in that, The historical reference trajectory is at least one of the following: The actual trajectory of the moving template from the previous production cycle; Alternatively, the average trajectory of the actual trajectories of the dynamic template over the most recent N production cycles.

5. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 1, characterized in that, The dynamic safety margin is the sum of the basic safety margin, the environmental risk margin, and the lateral axis dynamic braking distance. The basic safety margin includes the maximum braking distance of the manipulator and a fixed safety margin. The environmental risk margin is positively correlated with the fluctuation index. The lateral axis dynamic braking distance is positively correlated with the square of the lateral axis velocity of the manipulator.

6. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 5, characterized in that, The method for calculating the environmental risk margin is as follows: ； in, For environmental risk margin; The linear gain coefficient; For nonlinear gain coefficients; It is a volatility index; This is the set stability threshold.

7. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 2, characterized in that, Obtaining the instantaneous acceleration includes: The instantaneous velocity is obtained by performing a first-order difference on the real-time position; An estimated acceleration is obtained by applying a Kalman filter to the instantaneous velocity, and this estimated acceleration is used as the instantaneous acceleration.

8. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 1, characterized in that, The location of the synchronization target point for: ； in, for Dynamic safety margin at any time Let be the unit direction vector of the robot arm approaching the mold, pointing in the direction away from the moving mold plate. for Constantly follow the location of the target point.

9. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 1, characterized in that, Also includes: Set a dynamic speed limit for the lateral axis of the robotic arm; The dynamic speed limit is positively correlated with the set maximum speed and negatively correlated with the fluctuation index.

10. The method for coordinated motion control of a robotic arm and an injection molding machine according to claim 1, characterized in that, Also includes: Real-time monitoring of the actual distance between the robot's end effector and the surface of the moving template; When the actual distance is less than the set ratio of the dynamic safety margin, the safety protection mechanism is triggered, and the robot arm is controlled to retreat urgently in the direction away from the moving template.

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