Battery pack bottom guard plate automatic screwing device and method

Abstract

This invention relates to the field of battery pack assembly equipment technology for new energy vehicles, and particularly to an automatic screw-driving device and method for the bottom guard plate of a battery pack. The method includes a six-axis robot assembling the bottom guard plate to the battery pack; a first vision component locating four pre-locking holes and completing dispersed pre-locking; after successful pre-locking, establishing a first cross-station reference feature set based on the centers of at least three non-collinear pre-locking screw heads; after transfer to the downstream station, a second vision component re-identifies the same reference, the controller calculates and verifies the cross-station rigid coordinate transformation, converts the first-station predicted coordinates of the remaining screw holes into the current station's coarse predicted coordinates, and then establishes a local search area based on error budget for fine positioning and screw fastening. This invention's equipment can identify the screw fastening stage and judge anomalies based on the torque-angle full-process sequence, thereby reducing transport misalignment, improving multi-hole positioning efficiency, screw fastening consistency, and quality traceability.

Description

[Technical Field] This invention relates to the field of new energy vehicle power battery pack assembly equipment technology, and in particular to an automatic screw-driving device and method for the bottom guard plate of a battery pack. [Background Technology] The underbody protection plate of automotive power battery packs is typically characterized by its large area, relatively thin plate, and numerous screw holes distributed over a wide area. On existing production lines, the handling, assembly, alignment, and screw fastening of the underbody protection plate still suffer from several problems: significant manual intervention in handling, assembly, and screw fastening; potential slight relative displacement during cross-station transfer after assembly; time-consuming large-scale, hole-by-hole searches at downstream stations; and difficulty in distinguishing different abnormal fastening states based solely on the final torque.

[0001] Publication number CN109531118A discloses an automatic tightening device for battery pack covers and its operating method. It utilizes a conveyor line to transport trays, and a camera, pressing and positioning mechanism, and automatic tightening mechanism on a gantry robot arm complete the positioning of the cover holes and the tightening of bolts. This solution mainly addresses battery pack covers already carried by trays, but does not address the issue of establishing reliable constraints for large-size bottom plates after robotic assembly before transfer to the subsequent fastening station.

[0002] Publication number CN110740608A discloses an automatic installation device for a small battery pack PCB board, which includes a three-axis screw-locking mechanism with CCD at the screw-locking station. This solution does not address the automatic transfer of large-size bottom protective plates from the material cart to the battery pack, nor does it provide a process organization that involves "fixing with distributed screws before transfer and restoring the workpiece coordinates based on the same physical reference after transfer."

[0003] Publication number CN113909846A discloses a multi-degree-of-freedom oblique insertion automatic screw fastening machine, which includes a production line unit, a mounting unit, a CCD unit, a screw feeding unit, and a screw fastening unit. This solution is designed for oblique insertion product assembly and does not address the characteristics of large-area bottom guard plates that are prone to local bending, require cross-station transfer, and have a large number of distributed holes to be fastened, by forming a structure that reuses mechanical pre-locking and cross-station visual references.

[0004] CN213003668U discloses a screw fastening machine with floating lock missing lock detection and CCD vision positioning functions. It employs an X, Y, and Z axis linear module, a screw feeder, a servo intelligent electric screwdriver, and a CCD industrial camera for screw fastening. This solution improves the positioning and detection capabilities of a single screw fastening station, but it still does not solve the coordination problems between automatic bottom plate loading and unloading, immediate fixing after assembly, cross-station coordinate recovery after pre-locking, and precise positioning of local hole positions.

[0005] In the fields of industrial vision and automated tightening, existing technologies can predict screw hole positions using the overall workpiece pose and pre-stored design hole positions, and can also analyze tightening process data such as torque and angle. However, if each station re-performs a full-field search for all holes, it increases the vision cycle time; if the workpiece is directly treated as an absolutely rigid body, it is difficult to cover local manufacturing deviations and slight deflections in large-area thin plates. [Summary of the Invention] To overcome the above problems, this invention proposes an automatic screw-driving device and method for the bottom protective plate of a battery pack, which can effectively solve the above problems.

[0006] The present invention provides a technical solution to solve the above-mentioned technical problems: an automatic screw-driving device for battery pack bottom protection plates, comprising a conveyor line, a robot assembly, a pre-screwing assembly, at least one set of screw-driving assemblies, and a controller; the conveyor line has an installation pre-locking station and a screw-driving station located downstream of the installation pre-locking station along the conveying direction, for carrying and conveying the battery pack; the robot assembly is disposed on one side of the installation pre-locking station, comprising a six-axis robot and a suction cup assembly disposed at the end of the six-axis robot, the suction cup assembly being used to pick up the bottom protection plate from the bottom protection plate material cart and assemble the bottom protection plate onto the battery pack. Package; The pre-screw assembly corresponds to the pre-locking installation station setting, including a first moving mechanism, a first locking execution component, and a first vision component. The first locking execution component includes a first electric screwdriver. The first vision component is used to identify the pre-locking positioning features of the four pre-locking holes and determine four dispersed pre-locking positions before pre-locking. The first electric screwdriver is used to lock the pre-locking screws at the four pre-locking positions. After the pre-locking screws meet the pre-locking qualification conditions, the first vision component identifies at least three pre-locking screw head centers that are spaced apart from each other and not collinear, and establishes a first cross-station reference feature set according to the pre-locking position number; the screw-driving... The screw assembly, corresponding to the screw-driving station, includes a second moving mechanism, a second locking execution component, and a second vision component. The second locking execution component includes a second electric screwdriver. The controller stores the design coordinate set of screw holes on the bottom protective plate and, at the pre-locking installation station, converts the design coordinates of the screw holes to be locked into predicted coordinates of the first station based on the bottom protective plate pose obtained by the first vision component. After the battery pack is transferred to the current screw-driving station and positioned, the second vision component re-identifies the center of the pre-locked screw head corresponding to the first cross-station reference feature set to form a second cross-station reference feature set. The controller, based on... Two reference feature sets are used to obtain the two-dimensional rigid transformation relationship from the pre-locking station coordinate system to the current screw-driving station coordinate system, and the reference fitting residual is verified. When the reference fitting residual meets the preset condition, the predicted coordinates of the first station are converted into the coarse predicted coordinates of the current station through the two-dimensional rigid transformation relationship, and a local search area is established based on the coarse predicted coordinates. The second vision component is controlled to perform precise hole positioning in the local search area. The second moving mechanism drives the second electric screwdriver to complete the screw fastening according to the precise positioning result and the calibration relationship between the second vision component and the second electric screwdriver.

[0007] Preferably, the suction cup assembly includes a suction cup support frame connected to the end flange of the six-axis robot and a plurality of vacuum suction cups distributed on the suction cup support frame. The plurality of vacuum suction cups provide multi-point support for the bottom guard plate to reduce local sagging of the bottom guard plate during handling.

[0008] Preferably, the device further includes a position detection component and a stop positioning component connected to the controller; the position detection component is used to detect whether the battery pack has reached the installation pre-locking station or the screw-driving station, and the stop positioning component is used to position the battery pack at the corresponding station; the controller only activates the corresponding vision component and electric screwdriver after positioning is completed.

[0009] Preferably, the pre-screw assembly includes a first bracket spanning the outside of the conveyor line, the first moving mechanism includes a first transverse linear drive, a first longitudinal linear drive, and a first Z-axis assembly; the first vision assembly and the first electric screwdriver are disposed on the same moving end, and a screw feeder for supplying screws to the first electric screwdriver is provided on one side of the first bracket.

[0010] Preferably, there is a first coordinate mapping relationship between the imaging coordinate system of the first vision component, the device coordinate system of the first moving mechanism, and the locking axis of the first electric screwdriver, which has been calibrated. The controller converts the hole position coordinates obtained by the first vision component into the locking coordinates of the first electric screwdriver according to the first coordinate mapping relationship.

[0011] Preferably, the controller is configured to acquire images containing multiple hole positions or structural features once or in multiple steps by the first vision component, match at least three candidate features with the screw hole design coordinate set to obtain the first pose transformation relationship from the bottom guard plate design coordinate system to the installation pre-locking position coordinate system, and generate the first position prediction coordinates of the four pre-locking positions and the remaining screw holes to be locked from the first pose transformation relationship.

[0012] Preferably, the candidate features are obtained through at least one of circular hole detection, edge detection, contour matching, template matching, and a pre-trained target detection model; when the recognition confidence or the geometric consistency between the candidate features and the design features is lower than a preset threshold, the controller triggers re-image acquisition, adjustment of lighting parameters, or switching to another recognition method.

[0013] Preferably, the second moving mechanism includes a second bracket, a second transverse linear drive, a second longitudinal linear drive, and a second Z-axis assembly that spans the outside of the conveyor line, and the second electric screwdriver and the second vision assembly are disposed on the second Z-axis assembly; the imaging coordinate system of the second vision assembly, the equipment coordinate system of the second moving mechanism, and the locking axis of the second electric screwdriver have a second coordinate mapping relationship obtained by calibration.

[0014] Preferably, the four pre-locking positions are spaced apart circumferentially along the bottom guard plate and are not collinear. The first cross-station reference feature set and the second cross-station reference feature set each contain at least three pre-locking screw head centers. The fourth pre-locking screw head center is used to form redundant constraints, perform residual verification, or replace the reference feature when any reference feature fails to be identified.

[0015] Preferably, the two-dimensional rigid transformation relationship includes a rotation matrix R21 and a translation vector t21, wherein the rotation matrix R21 satisfies R21^T·R21=I and det(R21)=1; the controller obtains R21 and t21 by minimizing the coordinate residual between the corresponding feature points in the first cross-station reference feature set and the second cross-station reference feature set, and allows subsequent screw fastening to be performed when the root mean square residual of the reference fitting is not greater than a preset residual threshold.

[0016] Preferably, the four pre-locking positions are respectively set in the areas of the bottom guard plate that are spaced apart from each other; the pre-locking qualification conditions include each pre-locking screw reaching the lower limit of the preset fixed torque, the preset fixed torque being determined by process test, so that the clamping effect formed by the four pre-locking screws is sufficient to resist the maximum equivalent lateral load and rotational load applied to the bottom guard plate by the battery pack under subsequent transportation, acceleration, deceleration and vibration conditions.

[0017] Preferably, the controller sets the robot release interlock condition. After the six-axis robot completes the pre-locking at all four pre-locking positions and all pre-locking screws meet the pre-locking qualification condition, the suction cup assembly releases its adsorption. When the robot release interlock condition is not met, the suction cup assembly maintains its adsorption or pressure on the bottom guard plate.

[0018] Preferably, the screw-driving assembly consists of at least two sets arranged sequentially along the conveyor line. Each screw-driving station re-identifies the center of the pre-locked screw head and independently calculates the two-dimensional rigid transformation relationship corresponding to its own station. Each station only calls the set of screw holes to be locked allocated to its own station for coarse prediction, local fine positioning, and locking.

[0019] Preferably, for the j-th screw hole to be locked, the search radius or half-side length r_j of the local search area is determined according to r_j≥E_tr+E_fit+E_cal+E_def,j+M, where E_tr is the positioning uncertainty that still exists after the overall coordinate transformation after transfer, E_fit is the uncertainty corresponding to the benchmark fitting residual, E_cal is the calibration error between the vision component and the electric screwdriver, E_def,j is the manufacturing position deviation and local deformation allowance of the j-th hole position, and M is the preset safety margin.

[0020] Preferably, at least one of the first and second electric screwdrivers is a servo electric screwdriver capable of continuously outputting locking torque and rotation angle; the controller divides the locking process into an insertion and initial engagement stage, a low-load engagement stage, a mating stage, and a final tightening stage based on torque, angle, and the rate of change of torque with respect to angle, and extracts at least two features from the locking process sequence, including mating angle, peak torque, tightening angle after mating, torque slope during tightening stage, and stage duration angle, to determine whether there is floating lock, oblique lock, stripped teeth, incomplete engagement, or abnormal resistance in the locking process.

[0021] This invention also provides an automatic screw-driving method for a battery pack bottom cover plate, comprising: positioning the battery pack in an installation pre-locking station; using a six-axis robot to pick up the bottom cover plate from a bottom cover plate material cart via a suction cup assembly and assembling it into the battery pack; using a first vision component to identify the pre-locking positioning features of four pre-locking holes before pre-locking and determining four dispersed pre-locking positions; using a first electric screwdriver to lock the pre-locking screws at the four pre-locking positions, and releasing the suction cup assembly after the four pre-locking screws meet the pre-locking qualification conditions; using the first vision component to identify the center of the head of at least three pre-locking screws that are spaced apart from each other and not collinear, and establishing a first cross-station reference feature set according to the pre-locking position number; and converting the design coordinates of the remaining screw holes to be locked into the coordinates of the installation pre-locking station based on the bottom cover plate pose obtained by the first vision component. The system predicts the coordinates of the first station under the system; it then guides the pre-locked battery pack to the current screw-driving station downstream and positions it; it uses the second vision component to re-identify the center of the head of the same pre-locked screw, forming a second cross-station reference feature set; it calculates the two-dimensional rigid transformation relationship from the coordinate system of the pre-locked station to the coordinate system of the current screw-driving station based on the two reference feature sets and verifies the reference fitting residual; when the residual meets the preset conditions, it converts the predicted coordinates of the first station into the coarse predicted coordinates of the current station; it establishes a local search area near each coarse predicted coordinate based on the error budget, performs precise hole positioning within the local search area, and controls the second electric screwdriver to fasten the corresponding screws based on the precise positioning results and the calibration relationship between the second vision component and the second electric screwdriver; after all the specified screws are fastened to qualified condition, the battery pack flows out.

[0022] Preferably, the four pre-locking screws are first tightened to a preset fixed torque lower than the target tightening torque, wherein the preset fixed torque is not lower than the lower limit of the torque corresponding to the pre-locking qualification condition; after the remaining screws are tightened, the four pre-locking screws are tightened a second time by a second electric screwdriver or another downstream electric screwdriver until the corresponding target tightening torque is reached.

[0023] Preferably, the design coordinates of the j-th screw hole to be locked in the bottom plate design coordinate system are denoted as d_j, the first pose transformation from the design coordinate system to the pre-locking station coordinate system is represented as R1 and t1, and the two-dimensional rigid transformation from the pre-locking station coordinate system to the current screw-driving station coordinate system is represented as R21 and t21. Then the predicted coordinates of the first station are q_j(1)=R1d_j+t1, and the coarse predicted coordinates of the current station are q_j(2,0)=R21q_j(1)+t21. When the second vision component obtains the local correction amount Δq_j in the local search area, and the calibration offset vector from the detection center of the second vision component to the locking axis of the second electric screwdriver is o2, the final locking coordinates are q_j(2)=q_j(2,0)+Δq_j+o2.

[0024] Preferably, at least two screw-driving stations are set along the conveyor line, and the screw holes to be locked are assigned to different screw-driving stations according to their location or expected locking cycle time. Each time the battery pack enters a screw-driving station, at least three identical pre-locked screw head centers are re-identified, the two-dimensional rigid transformation relationship corresponding to this station is re-determined and verified, and then the coarse prediction, local fine positioning and locking of the hole position responsible for this station are completed.

[0025] Preferably, torque and rotation angle are continuously collected during the tightening process of at least some screws to form a complete tightening process sequence; abnormal points are eliminated and smoothed in the complete tightening process sequence, the rate of change of torque with angle is calculated, the stage boundaries of entry hole and initial engagement, low-load engagement, fit and final tightening are identified, and the tightening quality is judged based on the torque, angle, rate of change or stage duration angle characteristics of each stage; when an abnormality is judged, at least one of the following actions is performed: hole position marking, alarm, line stop, rework or secondary tightening.

[0026] Compared with the prior art, the automatic screw-driving device and method for the bottom guard plate of the battery pack of the present invention has the following advantages: 1. Four pre-locking screws establish mechanical clamping constraints before transfer and directly serve as cross-station visual references after pre-locking. The same physical object undertakes both mechanical fixing and visual reference functions. 2. A three-level coordinate chain is formed through the first station pose transformation, cross-station rigid transformation, and downstream local visual correction to avoid mixing the design coordinate system and the station coordinate system; 3. By establishing a state closed loop through benchmark fitting residual verification and robot release interlock, the risks of incorrect coordinate locking and unsecured bottom plate during transportation are reduced; 4. Determine the local search area using error budgeting to reduce invalid full-field searches for a large number of apertures; 5. It separates the overall rigid posture restoration from the local hole deformation compensation, which is suitable for large-area thin-bottom protective plates; 6. Utilize the characteristics of the entire locking and payment process for quality assessment to improve anomaly identification capabilities and quality traceability. [Attached Image Description] Figure 1 This is a schematic diagram of the overall structure and control relationship of the automatic screw-driving device for the bottom guard plate of the battery pack of the present invention.

[0027] Figure 2 This is a schematic diagram of the structure of the six-axis robot and suction cup assembly of the present invention.

[0028] Figure 3 This is a schematic diagram of the pre-screw assembly of the present invention.

[0029] Figure 4 This is a schematic diagram of the screw-driving assembly of the present invention.

[0030] Figure 5 This is a schematic diagram of the structure of the second Z-axis assembly of the present invention.

[0031] Figure 6 This is a flowchart illustrating the overall process of automatically screwing the bottom protective plate of the battery pack according to the present invention.

[0032] Explanation of reference numerals in the attached drawings: 10, conveyor line; 20, bottom guard plate trolley; 31, six-axis robot; 32, suction cup assembly; 40, pre-screw assembly; 41, first bracket; 42, first transverse linear drive; 43, first longitudinal linear drive; 44, first Z-axis assembly; 45, first vision assembly; 46, first electric screwdriver; 47, screw feeder; 50, screw-driving assembly; 51, second bracket; 52, second transverse linear drive; 53, second longitudinal linear drive; 54, second Z-axis assembly; 55, second vision assembly; 56, second electric screwdriver; 57, servo axis.

Detailed Implementation Methods

[0033] The purpose of this invention is to provide an automatic screw-driving device and method for battery pack bottom protection plates. After the pre-locking screws have been mechanically fixed, they can be used as a visual reference that can be repeatedly identified across workstations. The same physical object can be used to simultaneously achieve stable transport of the bottom protection plate and downstream coordinate recovery. The device also compensates for workstation transport errors, calibration errors, and local manufacturing or deformation deviations of the bottom protection plate through a two-level positioning method of overall rigid coordinate transformation plus predicted position local fine positioning. This ensures that the overall line cycle time, positioning accuracy, screw-driving consistency, and quality traceability are all taken into account.

[0034] To achieve the above objectives, the equipment provided by the present invention includes a conveyor line 10, a robot assembly, a pre-screw assembly 40, at least one set of screw-driving assemblies 50, and a controller. A pre-locking installation station is located upstream of the conveyor line 10, and at least one screw-driving station is located downstream of it. A six-axis robot 31 uses a suction cup assembly 32 to move the bottom guard plate from the bottom guard plate trolley 20 to the battery pack mounting surface; the suction cup assembly 32 maintains suction or pressure until a reliable threaded connection is formed on the bottom guard plate.

[0035] The first vision component 45 identifies the hole edges, adjacent contours, reinforcing rib intersections, or other pre-locking positioning features of the four pre-locking holes before pre-locking, and determines the four pre-locking positions. The first electric screwdriver 46 sequentially locks in the four pre-locking screws. The four pre-locking positions are spaced apart circumferentially along the bottom guard plate and are not collinear, preferably located near the four corners or opposite sides, so that the bottom guard plate obtains distributed clamping constraints.

[0036] The pre-locking qualification condition is used to ensure that the bottom guard plate maintains a predetermined relative position during robot release and subsequent transport. When using planar lateral sliding and rotation about a vertical axis as the verification objects, the clamping state corresponding to the preset fixed torque can be selected according to the following relationship: μ·ΣF_N,k ≥ K·F_d Σ(μ·F_N,k·r_k) ≥ K·M_d Where F_N,k is the effective clamping force formed by the k-th pre-locking screw, μ is the equivalent friction coefficient of the contact area between the bottom guard plate and the battery pack, F_d is the maximum equivalent lateral load under the predetermined conveying conditions, r_k is the equivalent force arm of the corresponding clamping action relative to the rotation check center, M_d is the maximum equivalent rotational load, and K is a safety factor greater than 1. In actual production, the preset fixed torque lower limit can be determined through process experiments based on screw specifications, connecting materials, and transport acceleration, rather than requiring a unique conversion of clamping force directly from torque.

[0037] Once all four pre-locking positions are secured and each pre-locking screw meets the pre-locking qualification conditions, the controller satisfies the robot's release interlock condition, allowing the six-axis robot 31 to release the vacuum adsorption. Subsequently, the first vision component 45 re-acquires images of the pre-locking area, using the centers of the heads of at least three pre-locking screws that are spaced apart from each other and not collinear as cross-station reference features, and establishes a first cross-station reference feature set B1 according to the pre-locking position number. Since these reference features are located on the pre-locking screws that have already fixed the bottom cover to the battery pack, there is no relative positional change between them and the bottom cover that might occur if additional visual markings were pasted on, thus simultaneously reflecting the mechanical fixing result and the visual reference position.

[0038] The controller pre-stores the set of screw hole design coordinates in the bottom guard plate design coordinate system D. The first vision component 45, at the pre-locking installation station, can determine the overall pose of the bottom guard plate relative to the first station coordinate system C1 through multiple hole positions or structural features. If the design coordinate is d_j, then the predicted coordinates of the j-th hole to be locked at the first station are expressed as: q_j(1) = R1 d_j + t1 Where R1 and t1 are the planar rotation matrix and translation vector from the bottom plate design coordinate system D to the first station coordinate system C1, respectively. These predicted coordinates are only used as the prior of the first station position for subsequent cross-station transfer and are not directly used as the final locking coordinates downstream.

[0039] After the battery pack is transferred to the current screw-driving station and positioned, the second vision component 55 re-identifies the centers of at least three pre-locked screw heads corresponding to B1, forming a second cross-station reference feature set B2. The coordinates of the i-th reference point in B1 under the first station coordinate system are denoted as p_i^(1), and the coordinates of the corresponding point in B2 under the current station coordinate system C2 are denoted as p_i^(2). The controller then calculates the two-dimensional rigid transformations R21 and t21 to minimize the following objective function: min Σ‖p_i^(2) (R21 p_i^(1) + t21)‖² Where R21 satisfies R21^T·R21=I and det(R21)=1, it is used to represent the rotation of the workpiece in the plane after transfer, and t21 represents the translation. Two-dimensional rigid transformation is preferred because the bottom guard plate is already fixed to the battery pack with pre-locking screws, and the overall pose change across workstations under normal working conditions is mainly manifested as translation and rotation; the size difference of the camera itself, lens distortion, and coordinate non-orthogonality are corrected through independent calibration at each workstation, and are not absorbed into the cross-workstation transformation as the actual movement of the bottom guard plate.

[0040] The controller further calculates the fitting residual e_i and the root mean square residual E_RMS for each benchmark point: e_i =‖p_i^(2) (R21 p_i^(1) + t21)‖ E_RMS =√[(1 / m)·Σe_i²] When E_RMS is not greater than the preset residual threshold, the current cross-station transformation is considered valid; when E_RMS exceeds the threshold, the controller will first trigger a re-photographing and re-identification of the reference features. If there are four pre-locked reference points, obvious abnormal points can be removed and the solution will be recalculated; if there are less than three valid reference points or the limit is still exceeded after recalculation, the locking will be stopped and an alarm will be triggered.

[0041] For the predicted coordinates q_j(1) of the first workstation, the coarse predicted coordinates of the current screw-driving workstation are: q_j(2,0) = R21 q_j(1) + t21 The controller establishes a local search region centered on the coarsely predicted coordinates. The search radius or half-side length r_j of this region is preferably determined according to the following formula: r_j ≥ E_tr + E_fit + E_cal + E_def,j + M Where E_tr is the positioning uncertainty remaining after the overall coordinate transformation following the transfer, E_fit is the uncertainty corresponding to the baseline fitting residual, E_cal is the calibration error between the current vision component and the electric screwdriver, E_def,j is the manufacturing position deviation and local deformation allowance of the j-th hole position, and M is the safety margin. The second vision component only identifies hole edges, threaded hole contours, adjacent structural corners, or other fixed structural features within this local search area, obtaining the local correction amount Δq_j. If the calibration offset vector from the detection center of the second vision component to the locking axis of the second electric screwdriver is o2, then the final locking coordinates are: q_j(2) = q_j(2,0) + Δq_j + o2 Therefore, the cross-station rigid transformation is only responsible for restoring the overall pose of the bottom guard plate, while the local fine positioning is responsible for compensating for manufacturing tolerances, local deflection, residual errors in datum fitting, and visual calibration errors at individual holes. The coarse predicted coordinates do not directly trigger the locking action; only after the local fine positioning is successful and passes visual validity judgment will the second electric screwdriver perform the locking action.

[0042] When two or more screw-driving stations are set up along conveyor line 10, each screw-driving station re-identifies at least three identical pre-locked screw head centers and independently calculates and verifies the cross-station rigidity transformation corresponding to this station, without using the transformation parameters of the previous screw-driving station. The holes to be locked are pre-assigned to each station according to their location, the number of screws, or the expected locking cycle time, in order to shorten the occupation time of a single station.

[0043] At least one of the first electric screwdriver 46 and the second electric screwdriver 56 is preferably a servo electric screwdriver. The controller continuously acquires the torque τ and rotation angle θ of a single screw, and can simultaneously acquire the rotational speed or motor current. Based on the torque level, angle increment, and g=Δτ / Δθ, the fastening process is divided into the insertion and initial engagement stage, the low-load engagement stage, the contact stage, and the final tightening stage, and features such as the contact angle, peak torque, tightening angle after contact, torque slope during the tightening stage, and stage duration angle are extracted. Basic quality judgment can be achieved through preset threshold rules, or statistical discrimination, probabilistic state discrimination, or pre-trained classifiers can be established based on qualified samples and known abnormal samples to further distinguish between floating locks, oblique locks, stripped teeth, incomplete engagement, and abnormal resistance.

[0044] Specifically, such as Figure 1-6 As shown, the equipment includes a conveyor line 10, a bottom guard plate trolley 20, a robot assembly, a pre-screw-driving assembly 40, two sets of screw-driving assemblies 50 arranged along the conveying direction, and a controller. The conveyor line 10 can be a roller conveyor, a double-speed chain conveyor, or a pallet-type conveyor. The pre-locking station and each screw-driving station are equipped with positioning detection devices and stop positioning devices; the positioning detection devices can be photoelectric sensors or proximity sensors, and the stop positioning devices can be a combination of a pneumatic stop and a lateral positioning mechanism. The controller can be a combination of an industrial computer, PLC, and vision controller, or an integrated industrial control platform.

[0045] Robot loading and release interlock The robot assembly includes a six-axis robot 31 and a suction cup assembly 32. The suction cup assembly 32 is connected to the end flange of the six-axis robot 31, and multiple vacuum suction cups are distributed on the suction cup support frame. The bottom guard plate trolley 20 is located within the working range of the six-axis robot 31. After the six-axis robot 31 picks up the bottom guard plate, it places it on the battery pack mounting surface, ensuring that the mounting holes are within the compensable range of the first vision assembly 45.

[0046] After the bottom guard plate is placed, the suction cup assembly 32 maintains adsorption or holds the bottom guard plate with a controlled holding force. The controller sets the robot release interlock conditions: the six-axis robot 31 is allowed to release the vacuum adsorption and exit the installation pre-locking station only when all four pre-locking positions are fully locked, the torque of each pre-locking screw reaches the pre-locking qualified lower limit, and no obvious abnormal locking state occurs; if any condition is not met, the adsorption is maintained and the transfer is suspended.

[0047] Pre-lock positioning and first station pose establishment The pre-driving screw assembly 40 includes a first bracket 41, a first transverse linear drive 42, a first longitudinal linear drive 43, a first Z-axis assembly 44, a first vision assembly 45, a first electric screwdriver 46, and a screw feeder 47.

[0048] The first vision component 45 uses a CCD industrial camera. The first vision component 45 and the first electric screwdriver 46 are located on the same moving end, and the spatial relationship between them is obtained through calibration.

[0049] Before pre-locking, the first vision component 45 acquires an image containing multiple hole positions at once, or acquires images in several predetermined imaging positions along with the first moving mechanism. The controller obtains at least three candidate hole positions or structural features and corresponds them to the design coordinate set through hole spacing, relative angle, adjacent contours or numbering relationships. The first station pose R1 and t1 can be obtained from at least three non-collinear corresponding points, and then the first station predicted coordinates of the four pre-locked positions and the remaining hole positions to be locked are generated according to q_j(1)=R1d_j+t1.

[0050] The four pre-locking positions use the hole edge, hole periphery contour, or adjacent fixed structure as "pre-locking positioning features" before pre-locking. These pre-locking positioning features are distinct from the subsequent "cross-station reference features" in terms of timing and function: the former is used to determine the pre-locking hole position before the screw is locked, while the latter is formed by the center of the pre-locked screw head after pre-locking is completed. Therefore, there is no problem of relying on the screw head that has not yet appeared to determine the pre-locking position.

[0051] Four-point pre-locking and establishment of the first cross-station reference feature set The four pre-locking positions are preferably located near the four corners or opposite sides of the bottom guard plate and are not collinear. The first electric screwdriver 46 is used to sequentially tighten the four pre-locking screws. The preset fixing torque can be equal to or lower than the target locking torque; when using low torque pre-locking, the preset fixing torque must not be lower than the minimum acceptable pre-locking torque to ensure stable transport of the bottom guard plate.

[0052] After the four pre-locked screws meet the pre-locking qualification conditions, the first vision component 45 acquires images again, identifies at least three pre-locked screw head centers, and saves them as the first cross-station reference feature set B1 according to the pre-locking position number. Preferably, four pre-locked screw head centers are identified simultaneously, with more than three used to solve the rigidity transformation, and the remaining points forming redundant constraints and used for residual verification. The three reference points used for solving are not collinear, and preferably cover as large a bottom guard plate plane area as possible to reduce the amplification of local pixel errors on the rotation angle estimation.

[0053] Downstream cross-station rigid coordinate reconstruction and effectiveness verification The screw-driving assembly 50 includes 51, a second bracket 51, a second transverse linear drive 52, a second longitudinal linear drive 53, a second Z-axis assembly 54, a second vision assembly 55, and a second electric screwdriver 56. The second Z-axis assembly 54 includes a servo axis 57, and the second vision assembly 55 and the second electric screwdriver 56 are both disposed on the servo axis 57. The first Z-axis assembly 44 may adopt the same structure as the second Z-axis assembly 54.

[0054] After pre-locking is completed, conveyor line 10 transports the battery pack to the current screw-driving station. The second vision component 55 re-identifies the center of the pre-locked screw head with the same number as B1, forming a second cross-station reference feature set B2. The controller uses the least squares method to obtain R21 and t21 based on the corresponding reference points, and forces R21 to satisfy orthogonal constraints and unit determinant constraints.

[0055] The controller calculates E_RMS and compares it with the preset residual threshold. If the residual exceeds the limit, the exposure is re-exposed or the lighting is adjusted and the image is re-acquired; if it still exceeds the limit and four reference points are currently identified, the reference point with the largest deviation can be removed and the remaining three non-collinear reference points can be used to resolve the problem; if there are fewer than three valid reference points or the re-solution still fails, the second electric screwdriver 56 is prohibited from pressing and locking and an alarm is output.

[0056] Third-level coordinate chain, local search region, and final locked coordinates The bottom guard plate design coordinate system D is first transformed to the pre-locking installation coordinate system C1 through R1 and t1 to obtain the predicted coordinates q_j(1) of the first station; then it is transformed to the current screw-driving station coordinate system C2 through R21 and t21 to obtain the coarse predicted coordinates q_j(2,0). These two transformations correspond to the "actual placement posture of the design part relative to the first station" and the "overall transfer posture of the same workpiece fixed by pre-locking from the first station to the current station", respectively, and the two are not used interchangeably.

[0057] The coarse prediction coordinates are only used to establish the local search area. The size of the local search area should cover the remaining uncertainty of the transfer, the benchmark fitting residual, the visual calibration error, the single-hole manufacturing position deviation, and the local deflection. The second vision component 55 obtains the local correction amount Δq_j within the local search area and converts it to the locking axis according to the second coordinate mapping relationship between the second vision component 55 and the second electric screwdriver 56. The final locking coordinates are determined according to q_j(2)=q_j(2,0)+Δq_j+o2.

[0058] For large-area thin bottom plates, the cross-station rigidity transformation is not used to assume that all holes are completely free from local deformation relative to the reference point, but only to obtain the prior search positions of the holes; local manufacturing tolerances, minor warping, and single-hole position errors of the bottom plate are absorbed by downstream local precision positioning. Therefore, even if the bottom plate cannot be regarded as an ideal rigid body, it does not affect the implementation of this secondary positioning scheme.

[0059] Multi-workstation area allocation When two or more screw-driving assemblies 50 are set up, each screw-driving station independently performs B2 recognition, R21 / t21 solution, E_RMS verification, and local fine positioning. Each station does not use the coordinate transformation parameters of the previous station. The controller can assign the hole set to different stations according to the front and rear areas, left and right areas, number of holes, or historical average visual positioning and fastening time of the bottom guard plate.

[0060] Quality assessment of the entire locking process The second electric screwdriver 56 preferably uses a servo electric screwdriver. The controller continuously collects torque τ and rotation angle θ starting from the moment a single screw begins to be tightened, and performs outlier removal and necessary smoothing. The controller calculates the angle increment, torque increment, and g=Δτ / Δθ, and combines them with process thresholds to identify the entry hole and the initial engagement stage, low-load engagement stage, contact stage, and final tightening stage.

[0061] If the final torque reaches the target range but the tightening angle is significantly insufficient after bonding, it can indicate the risk of premature jamming, cross-locking, or oblique locking. If the final torque fails to reach the target for an extended period and the rotation angle increases abnormally, it can indicate the risk of stripping. If abnormally high torque occurs before bonding, it can indicate that the hole position is not aligned or the initial engagement is abnormal. When the locking result is abnormal, the controller records the hole position number, the current station, and the corresponding torque-angle process data, and executes alarms, line stoppages, rework, or secondary locking according to the production strategy.

[0062] Complete Workflow In step S1, the conveyor line 10 sends the battery pack into the installation pre-locking station. After the arrival detection component is triggered, the stop positioning component completes the positioning.

[0063] In step S2, the six-axis robot 31 picks up the bottom protective plate from the bottom protective plate trolley 20 and places it on the battery pack mounting surface, while the suction cup assembly 32 holds it in place.

[0064] In step S3, the first vision component 45 identifies the pre-locking positioning features of the four pre-locking holes and generates pre-locking position coordinates based on the pose of the first workstation.

[0065] Step S4: The first electric screwdriver 46 sequentially screws in the four pre-locking screws and confirms that the pre-locking is qualified.

[0066] In step S5, the controller satisfies the robot release interlock condition, and the six-axis robot 31 releases its adsorption and exits.

[0067] In step S6, the first vision component 45 identifies at least three non-collinear pre-locked screw head centers and saves the first cross-station reference feature set B1.

[0068] In step S7, the conveyor line 10 delivers the battery pack to the current screw-driving station, and the second vision component 55 re-identifies the center of the same screw head to form B2.

[0069] Step S8: The controller calculates R21 and t21 and verifies E_RMS; if they fail, it will re-identify or trigger an alarm.

[0070] Step S9: The controller converts the predicted coordinates of the first station under its responsibility into the coarse predicted coordinates of the current station, and establishes the ROI based on the error budget.

[0071] In step S10, the second vision component 55 completes the precise positioning of the hole within the ROI, and the second electric screwdriver 56 locks the hole according to the final locking coordinates.

[0072] Step S11: The controller records the torque-angle process and completes the quality determination.

[0073] Step S12: In the case of multiple workstations, repeat steps S7 to S11 at the next workstation.

[0074] Step S13: If the pre-locking screws are tightened with a fixed torque lower than the target torque, then after the other screws are tightened, the four pre-locking screws are tightened a second time.

[0075] Step S14: After all specified holes have qualified locking records, release the stop and output the battery pack.

[0076] When switching between different battery pack specifications, the changeover can be completed by replacing the suction cup support frame, adjusting the vacuum suction cup position, and calling the corresponding design hole coordinate set, pre-lock position number, vision template, station calibration parameters, and locking parameters. The first vision component 45 and the second vision component 55 can use either a CCD industrial camera or a CMOS industrial camera. Each station periodically verifies the mapping error from vision coordinates to equipment coordinates using a standard calibration board or known-size tooling; when the mapping error exceeds the maintenance threshold, the mapping relationship from the vision inspection center to the corresponding electric screwdriver locking axis is recalibrated.

[0077] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any modifications, equivalent substitutions and improvements made within the concept of the present invention should be included within the patent protection scope of the present invention.

Claims

1. An automatic screw-driving device for the bottom protective plate of a battery pack, characterized in that, The system includes a conveyor line, a robot assembly, a pre-screw-driving assembly, at least one set of screw-driving assemblies, and a controller. The conveyor line has a pre-locking installation station and a screw-driving station downstream of the pre-locking installation station, used to carry and transport the battery pack. The robot assembly is located on one side of the pre-locking installation station and includes a six-axis robot and a suction cup assembly at the end of the six-axis robot. The suction cup assembly is used to pick up the bottom guard plate from the bottom guard plate material cart and assemble the bottom guard plate into the battery pack. The pre-screw-driving assembly is located corresponding to the pre-locking installation station and includes a first moving mechanism, a first locking execution assembly, and a first vision assembly. The first locking execution assembly includes a first electric screwdriver. The first vision assembly is used to identify the pre-locking positioning features of four pre-locking holes and determine four dispersed pre-locking positions before pre-locking. The first electric screwdriver is used to lock the pre-locking screws into the four pre-locking positions. After the pre-locking screws meet the pre-locking qualification conditions, the first vision component identifies at least three pre-locking screw head centers that are spaced apart and not collinear, and establishes a first cross-station reference feature set according to the pre-locking position number; the screw-driving component is set corresponding to the screw-driving station and includes a second moving mechanism, a second locking execution component, and a second vision component, the second locking execution component including a second electric screwdriver; the controller stores the screw hole design coordinate set of the bottom guard plate, and converts the design coordinates of the screw holes to be locked into the first station predicted coordinates according to the bottom guard plate pose obtained by the first vision component at the installation pre-locking station; after the battery pack is transferred to the current screw-driving station and positioned, the second vision component re-identifies the first cross-station reference feature set. The center of the pre-locked screw head corresponding to the quasi-feature set is used to form a second cross-station reference feature set. The controller obtains the two-dimensional rigid transformation relationship from the pre-locked station coordinate system to the current screw-driving station coordinate system based on the two reference feature sets and verifies its reference fitting residual. When the reference fitting residual meets the preset condition, the first station predicted coordinate is converted into the current station coarse predicted coordinate through the two-dimensional rigid transformation relationship, and a local search area is established based on the coarse predicted coordinate. The second vision component is controlled to perform hole position fine positioning in the local search area. The second moving mechanism drives the second electric screwdriver to complete the corresponding screw fastening based on the fine positioning result and the calibration relationship between the second vision component and the second electric screwdriver.

2. The automatic screw-driving equipment for the bottom protective plate of the battery pack according to claim 1, characterized in that, The suction cup assembly includes a suction cup support frame connected to the end flange of the six-axis robot and multiple vacuum suction cups distributed on the suction cup support frame. The multiple vacuum suction cups provide multi-point support for the bottom guard plate to reduce local sagging of the bottom guard plate during transportation.

3. The automatic screw-driving equipment for the bottom protective plate of the battery pack according to claim 1, characterized in that, It also includes a position detection component and a stop positioning component connected to the controller; the position detection component is used to detect whether the battery pack has reached the installation pre-locking station or the screw-driving station, and the stop positioning component is used to position the battery pack at the corresponding station. The controller only activates the corresponding vision component and electric screwdriver after the positioning is completed.

4. The automatic screw-driving equipment for the bottom protective plate of the battery pack according to claim 1, characterized in that, The pre-driving screw assembly includes a first bracket spanning the outside of the conveyor line; the first moving mechanism includes a first transverse linear drive, a first longitudinal linear drive, and a first Z-axis assembly; the first vision assembly and the first electric screwdriver are disposed on the same moving end; and a screw feeder for supplying screws to the first electric screwdriver is provided on one side of the first bracket.

5. The automatic screw-driving equipment for the bottom protective plate of the battery pack according to claim 4, characterized in that, The imaging coordinate system of the first vision component, the device coordinate system of the first moving mechanism, and the locking axis of the first electric screwdriver have a first coordinate mapping relationship obtained through calibration. The controller converts the hole position coordinates obtained by the first vision component into the locking coordinates of the first electric screwdriver according to the first coordinate mapping relationship.

6. The automatic screw-driving equipment for the bottom protective plate of the battery pack according to claim 1, characterized in that, The controller is configured to acquire images containing multiple hole positions or structural features once or in multiple steps by a first vision component, match at least three candidate features with the screw hole design coordinate set to obtain the first pose transformation relationship from the bottom guard plate design coordinate system to the installation pre-locking position coordinate system, and generate the first position prediction coordinates of the four pre-locking positions and the remaining screw holes to be locked from the first pose transformation relationship.

7. The automatic screw-driving equipment for the bottom protective plate of the battery pack according to claim 6, characterized in that, Candidate features are obtained through at least one of circular hole detection, edge detection, contour matching, template matching, and a pre-trained target detection model; when the recognition confidence or the geometric consistency between the candidate feature and the design feature is lower than a preset threshold, the controller triggers re-image acquisition, adjusts lighting parameters, or switches to another recognition method.

8. The automatic screw-driving equipment for the bottom protective plate of the battery pack according to claim 1, characterized in that, The second moving mechanism includes a second bracket spanning the outside of the conveyor line, a second transverse linear drive, a second longitudinal linear drive, and a second Z-axis assembly. The second electric screwdriver and the second vision assembly are mounted on the second Z-axis assembly. The imaging coordinate system of the second vision assembly, the equipment coordinate system of the second moving mechanism, and the locking axis of the second electric screwdriver have a second coordinate mapping relationship obtained through calibration.

9. The automatic screw-driving equipment for the bottom protective plate of the battery pack according to claim 1, characterized in that, The four pre-locking positions are spaced apart circumferentially along the bottom guard plate and are not collinear. The first cross-station reference feature set and the second cross-station reference feature set each contain at least three pre-locking screw head centers. The fourth pre-locking screw head center is used to form redundant constraints, perform residual verification, or replace the reference feature when any reference feature fails to be identified.

10. A method for automatically screwing screws onto the bottom protective plate of a battery pack, characterized in that, include: The battery pack is moved into the pre-locking installation station and positioned; a six-axis robot uses a suction cup assembly to pick up the bottom protective plate from the bottom protective plate material cart and assemble it into the battery pack. The first vision component identifies the pre-locking positioning features of four pre-locking holes before pre-locking and determines four dispersed pre-locking positions. A first electric screwdriver is used to lock the pre-locking screws at the four pre-locking positions. After the four pre-locking screws meet the pre-locking qualification conditions, the suction cup assembly is released. The first vision component identifies the center of the heads of at least three pre-locking screws that are spaced apart and not collinear, and establishes a first cross-station reference feature set according to the pre-locking position number. Based on the bottom plate pose obtained by the first vision component, the design coordinates of the remaining screw holes to be locked are converted into the first station predicted coordinates under the pre-locking station coordinate system. The pre-locked battery pack is then moved to the downstream current screw-driving station and positioned. The second vision component is used to re-identify the center of the same pre-locked screw head, forming a second cross-station reference feature set; the two-dimensional rigid transformation relationship from the pre-locked station coordinate system to the current screw-driving station coordinate system is obtained based on the two reference feature sets, and the reference fitting residual is verified; when the residual meets the preset conditions, the predicted coordinates of the first station are converted into the coarse predicted coordinates of the current station; a local search area is established near each coarse predicted coordinate based on the error budget, and the hole position is precisely located within the local search area; based on the precise location result and the calibration relationship between the second vision component and the second electric screwdriver, the second electric screwdriver is controlled to fasten the corresponding screw; after all the specified screws are fastened to qualified condition, the battery pack is discharged.

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