A robotic arm with adaptive mechanical positioning tooling
The robotic arm, driven by a hydraulic pump, uses hydraulic pressure to generate suction to pick up the workpiece, solving the problem of insufficient friction in traditional positioning fixtures and achieving stable workpiece fixation and improved accuracy.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- YANGZHOU YANHUI INTELLIGENT TECH CO LTD
- Filing Date
- 2026-05-09
- Publication Date
- 2026-06-30
AI Technical Summary
Traditional rigid positioning fixtures are difficult to stably fit free-form surfaces or complex contour workpieces, resulting in insufficient friction during positioning and frequent object slippage.
The robotic arm, driven by a hydraulic pump, moves from the movable column at the head end to the positioning column at the tail end by squeezing. It uses hydraulic pressure to generate suction, which causes the support head to adhere and fix the workpiece. The stability is improved by combining a reset mechanism and an elastic oil bladder.
It achieves firm and stable adsorption of the workpiece, avoids the slippage problem caused by insufficient friction, and improves positioning accuracy and stability.
Smart Images
Figure CN122299700A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of machining positioning fixture technology, and in particular to a robotic arm with an adaptive mechanical positioning fixture. Background Technology
[0002] In manufacturing sectors such as machining, assembly, and testing, positioning fixtures are core foundational equipment for ensuring workpiece machining accuracy, assembly consistency, and production efficiency. Their performance directly determines product quality and production cycle time. As the manufacturing industry shifts towards multi-variety, small-batch, and personalized customization, and as workpiece complexity and precision requirements continue to increase, traditional rigid positioning fixtures can no longer meet actual production needs. There is an urgent need for a positioning fixture with adaptive capabilities to address the pain points of existing technologies.
[0003] The shortcomings of existing technologies are that, since the positioning surfaces of existing rigid positioning fixtures are mostly flat or regular curved surfaces, they cannot achieve stable fitting and positioning for free curved surfaces, complex contour workpieces, and cast or forged blanks. The support heads used for object contact all use friction to limit the object. When the friction is insufficient to support the object, the limiting object will slide. Summary of the Invention
[0004] The purpose of this invention is to provide a robotic arm with an adaptive mechanical positioning fixture. By squeezing the movable column at the head end to move towards the positioning column at the tail end, a hydraulic pump is activated to pump oil out of the fixed frame, increasing the oil pressure inside the fixed frame. This causes the support head connected to the movable column at the head end to generate suction. Furthermore, the movable column at the head end moves to the positioning column at the tail end and is braked by the oil pressure, thus enabling the support head to adsorb and fix the object it is in contact with. This improves the object's positioning and makes the adsorption more secure and stable, preventing the object from sliding due to insufficient friction of the support head.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: a robotic arm with an adaptive mechanical positioning fixture, comprising a robotic arm and a support platform; symmetrical movable blocks are provided at one end of the support platform, a fixed frame is fixedly connected to one end of the movable blocks, a hydraulic pump is provided at the top of the fixed frame, and a flow-concentrating hood is provided at one end of the fixed frame; it also includes a support member, which consists of a head movable column, a support head, and a tail positioning column. The head movable column is slidably connected to the fixed frame, and the tail positioning column is located inside the fixed frame. A linkage is provided between the tail positioning column and the head movable column; when the support head abuts against an object, the fixed frame fixed to the movable blocks is driven to converge by the support platform, and the support head, under force, drives the head movable column to move towards the tail positioning column through the linkage. The hydraulic pump drives the oil in the fixed frame to move, so that the tail positioning column locks the head movable column and the object is adsorbed and fixed by the support head.
[0006] As a further description of the above technical solution: An inner cylinder is fixedly connected to the tail end positioning post, and a flow cavity is provided between the inner cylinder and the tail end positioning post. A guide hole is symmetrically provided at one end of the inner cylinder, and the guide hole connects the inner cylinder and the flow cavity.
[0007] As a further description of the above technical solution: One end of the tail-end positioning post is fixedly connected to an elastic oil bladder, and the elastic oil bladder is connected to the inner cylinder. The end of the tail-end positioning post near the elastic oil bladder is movably provided with a connecting tube. One end of the connecting tube passes through the tail-end positioning post and is connected to the flow cavity. The other end of the connecting tube is fixedly connected to a head-end movable post.
[0008] As a further description of the above technical solution: A fixing ring is fixed to one end of the connecting pipe near the head end movable column, and the fixing ring limits the connecting pipe to the head end movable column. A limiting tube is fixed to one end of the connecting pipe near the fixing ring, and the limiting tube is located inside the head end movable column.
[0009] As a further description of the above technical solution: A piston block is movably connected inside the built-in cylinder. A support rod is fixed to one end of the piston block. An air guide pipe is provided inside the support rod. One end of the air guide pipe is connected to the flow-concentrating hood, and the other end of the air guide pipe is connected to the head end movable column.
[0010] As a further description of the above technical solution: A piston cylinder is fixedly connected inside the movable column at the head end. A connecting pipe is fixedly connected to one end of the piston cylinder. A locking block is fixedly connected to one end of the connecting pipe. A ball groove is opened inside the locking block, and the ball groove is connected to the connecting pipe.
[0011] As a further description of the above technical solution: A piston block two is movably disposed inside the piston cylinder. The piston block two is slidably connected to the support rod. One end of the piston block two is fixedly connected to the support rod, and one end of the support rod is fixedly connected to the abutment block.
[0012] As a further description of the above technical solution: One end of the support head is fixedly connected to a ball head, and the ball head is adapted to the ball groove. A connecting groove is opened in the support head and the ball head, and the connecting groove is connected to the ball groove.
[0013] As a further description of the above technical solution: The head end movable column has a directional sliding groove at one end near the locking block, and the directional sliding groove is slidably connected to a reset mechanism.
[0014] As a further description of the above technical solution: The reset mechanism includes a slide rod, which is adapted to a directional sliding mechanism. One end of the slide rod is fixedly connected to a collar, one end of the collar is fixedly connected to a tension spring, and the other end of the tension spring is fixedly connected to a locking block. The other end of the slide rod is fixedly connected to a fixing ring, one end of the fixing ring is fixedly connected to a stop ring, and a support head is provided inside the stop ring.
[0015] This invention provides a robotic arm with an adaptive mechanical positioning fixture, which has the following advantages: In this invention, by squeezing the movable column at the head end to move towards the positioning column at the tail end, the hydraulic pump is activated to pump the oil in the fixed frame outward, thereby increasing the oil pressure in the fixed frame. This causes the support head connected to the movable column at the head end to generate suction. Furthermore, the movable column at the head end moves to the positioning column at the tail end and is braked by the oil pressure, thus enabling the support head to adsorb and fix the object it is in contact with. This improves the object's positioning and makes the adsorption more secure and stable, preventing the object from sliding due to insufficient friction of the support head. Attached Figure Description
[0016] Figure 1 This is a schematic diagram of the structure of a robotic arm with an adaptive mechanical positioning fixture proposed in this invention; Figure 2 This is a schematic diagram of the fixed frame structure in this invention; Figure 3 This is a schematic diagram of the elastic oil bladder in this invention; Figure 4 In this invention Figure 3 Enlarged view of point A in the middle; Figure 5 In this invention Figure 3 Enlarged view of point B in the middle; Figure 6 This is a schematic diagram of the structure of the movable column at the head end in this invention; Figure 7 This is a schematic diagram of the structure of piston block two in this invention; Figure 8 This is a schematic diagram of the collar structure in this invention; Figure 9 This is a schematic diagram of the tail-end positioning post in this invention; Figure 10 This is a schematic diagram of the ball head structure in this invention.
[0017] Legend: 1. Robotic arm; 2. Support platform; 3. Movable block; 4. Fixed frame; 5. Flow hood; 6. Hydraulic pump; 7. Support component; 71. Head end movable column; 711. Locking block; 712. Piston cylinder; 713. Connecting pipe; 714. Ball groove; 715. Connecting port; 716. Mounting groove; 717. Orientation groove; 72. Support head; 721. Ball head; 7201. Cross groove; 7202. Orientation block; 722. Connecting groove; 73. Tail end positioning. 731. Column; 732. Internal cylinder; 733. Guide hole; 733. Connecting pipe; 7331. Limiting pipe; 7332. Fixing ring; 74. Linking component; 741. Support rod; 7411. Limiting ring; 742. Piston block one; 743. Piston block two; 7431. Support rod; 7432. Abutment block; 75. Air guide pipe; 76. Reset mechanism; 761. Collar; 762. Slide rod; 763. Fixing ring; 764. Abutment ring; 765. Tension spring; 77. Elastic oil bladder. Detailed Implementation
[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0019] Reference Figure 1-10 A robotic arm with an adaptive mechanical positioning fixture includes a robotic arm 1, a support platform 2, and a movable block 3 symmetrically arranged at one end of the support platform 2. A fixed frame 4 is fixedly connected to one end of the movable block 3, and a hydraulic pump 6 is provided at the top of the fixed frame 4. A flow-concentrating hood 5 is provided at one end of the fixed frame 4. The support also includes a support member 7, which consists of a head movable column 71, a support head 72, and a tail positioning column 73. The head movable column 71 is slidably connected to the fixed frame 4, and the tail positioning column 73 is located inside the fixed frame 4. A linkage 74 is provided between the tail positioning column 73 and the head movable column 71. When the support head 72 abuts against an object, the fixed frame 4 fixed to the movable block 3 is driven to converge by the support platform 2. The support head 72 is forced to move the head movable column 71 towards the tail positioning column 73 through the linkage 74. The hydraulic pump 6 drives the oil in the fixed frame 4 to move, so that the tail positioning column 73 locks the head movable column 71 and the object is adsorbed and fixed by the support head 72.
[0020] Specifically, the robotic arm 1 is a multi-axis robotic arm 1 in the prior art. A symmetrically sliding movable block 3, fixed to a support platform 2 at one end of the robotic arm 1, drives a fixed frame 4, to which the two movable blocks 3 are fixed, to converge or disperse via hydraulic or pneumatic means. A hydraulic pump 6, fixed to the top of the fixed frame 4, controls the oil inside the fixed frame 4. A flow-concentrating hood 5, fixed to one end of the fixed frame 4, can be connected to an external suction device via a pipe. When the support platform 2 drives the movable block 3 to converge the fixed frame 4, a support head 72 located in the fixed frame 4 presses against the object. 2. It can fit against the surface of the object and move from the head end movable column 71 to the tail end positioning column 73 by squeezing. The hydraulic pump 6 is started to pump the oil in the fixed frame 4 outward, which increases the oil pressure in the fixed frame 4. This causes the support head 72 connected to the head end movable column 71 to generate suction. The head end movable column 71 moves to the tail end positioning column 73 and is braked by the oil pressure. This allows the support head 72 to adsorb and fix the object it is in contact with. After the object is limited, the adsorption is more firm and stable, and the object limited by the support head 72 is prevented from sliding due to insufficient friction of the support head 72.
[0021] An inner cylinder 731 is fixedly connected inside the tail-end positioning post 73, and a flow cavity is provided between the inner cylinder 731 and the tail-end positioning post 73. A guide hole 732 is symmetrically provided at one end of the inner cylinder 731, and the guide hole 732 communicates the inner cylinder 731 with the flow cavity. An elastic oil bladder 77 is fixedly connected to one end of the tail-end positioning post 73, and the elastic oil bladder 77 communicates with the inner cylinder 731. A connecting tube 733 is movably provided at the end of the tail-end positioning post 73 near the elastic oil bladder 77. One end of the connecting tube 733 passes through the tail-end positioning post 73 and communicates with the flow cavity. The other end of the connecting tube 733 is fixedly connected to a head-end movable post 71. A fixing ring 7332 is fixedly connected to the end of the connecting tube 733 near the head-end movable post 71, and the fixing ring 7332 limits the connecting tube 733 to the head-end movable post 71. A limiting tube 7332 is fixedly connected to the end of the connecting tube 733 near the fixing ring 7332. 331, and the limiting tube 7331 is located inside the head end movable column 71; a piston block 742 is movably connected inside the inner cylinder 731, a support rod 741 is fixedly connected to one end of the piston block 742, a duct 75 is provided inside the support rod 741, one end of the duct 75 is connected to the flow hood 5, and the other end of the duct 75 is connected to the head end movable column 71; a piston cylinder 712 is fixedly connected inside the head end movable column 71, a connecting pipe 713 is fixedly connected to one end of the piston cylinder 712, a locking block 711 is fixedly connected to one end of the connecting pipe 713, a ball groove 714 is opened inside the locking block 711, and the ball groove 714 is connected to the connecting pipe 713; a piston block 743 is movably provided inside the piston cylinder 712, the piston block 743 is slidably connected to the support rod 741, a support rod 7431 is fixedly connected to one end of the piston block 7433, and a stop block 7432 is fixedly connected to one end of the support rod 7431; Specifically, the inner cylinder 731 of the tail-end positioning post 73 is connected to the elastic oil bladder 77 and the flow cavity respectively. A piston block 742 is movably connected inside the inner cylinder 731, and the piston block 742 passes through the movable post 71 at the fixed end of the inner cylinder 731. The elastic oil bladder 77 is reserved with oil for the piston block 742 to fill as it moves along the inner cylinder 731. When the piston block 742 moves away from the elastic oil bladder 77 along the inner cylinder 731, the piston block 742 directs the oil in the inner cylinder 731 to the flow cavity through the guide hole 732. The oil in the flow cavity flows to the movable post at the head end through the connecting pipe 713 that passes through the tail-end positioning post 73. In the piston cylinder 712 fixed inside the column 71, the mounting groove 716 of the piston cylinder 712 is used to install the limiting tube 7331 fixed to the connecting pipe 733. A connecting port 715 is provided at one end of the piston cylinder 712 near the mounting groove 716, which connects the piston cylinder 712 to the inner cavity of the fixed frame 4. When the support head 72 drives the movable column 71 at the head end to move, the piston block 742 fixed to the support rod 741 draws the oil in the inner cylinder 731 through the flow chamber and along the connecting pipe 713 into the piston cylinder 712. The hydraulic pump 6 is started to pressurize the oil in the fixed frame 4. The piston block 742, which is slidably connected in the piston cylinder 712, is also activated. 43 moves directionally along the support rod 741 under oil pressure. The piston cylinder 712 is located in one end of the connecting pipe 713 and is connected to the connecting groove 722 of the support head 72 through the connecting pipe 713. One end of the support rod 741 located inside the piston cylinder 712 is fixed with a limiting ring 7411. The limiting ring 7411 is used to limit the piston block 743. When the support head 72 is attached to the surface of the object to form a sealed structure, the movement of the piston block 743 along the piston cylinder 712 generates negative pressure, which facilitates the adsorption and fixation of the object abutting the support head 72, maintaining its own stability. When the support head 72 is attached to the surface of the object and does not form a sealed structure, the piston block 743 moves along the piston cylinder 712 to form a sealed structure. 3. Under the pressure of the oil, the support rod 741 moves in a directional manner and moves to the limiting tube 7331 fixed to the connecting tube 733. This makes the flow chamber connected by the limiting tube 7331 and the inner cylinder 731 form a sealed structure, limiting the piston block 742 fixed to the head end movable column 71 in the inner cylinder 731. The abutment block 7432 fixed to one end of the piston block 743 abuts against the air guide tube 75, so that the air guide tube 75 connects the support head 72 to the flow hood 5. The external suction device generates suction at the support head 72, so that the support head 72 can adsorb and fix the object by its own friction and the generated suction, thereby improving the stability of the object itself.
[0022] One end of the support head 72 is fixedly connected to a ball head 721, and the ball head 721 is adapted to the ball groove 714. A connecting groove 722 is opened in the support head 72 and the ball head 721, and the connecting groove 722 is connected to the ball groove 714. The end of the head end movable column 71 near the locking block 711 is provided with a directional sliding groove 717, and a reset mechanism 76 is slidably connected to the directional sliding groove 717. The reset mechanism 76 includes a slide rod 762, and the slide rod 762 is adapted to the directional sliding. One end of the slide rod 762 is fixedly connected to a collar 761, one end of the collar 761 is fixedly connected to a tension spring 765, and the other end of the tension spring 765 is fixedly connected to the locking block 711. The other end of the slide rod 762 is fixedly connected to a fixing ring 763, one end of the fixing ring 763 is fixedly connected to a stop ring 764, and the stop ring 764 is provided with a support head 72. Specifically, when the support head 72 is installed, the support head 72 is installed in the support head 72. When the support head 72 abuts against the surface of the object, the ball head 721 fixed to the support head 72 can be used to improve the fit between the support head 72 and the surface of the object. The cross groove 7201 opened at one end of the ball head 721 engages with the directional block 7202 fixed in the locking block 711. The directional block 7202 is used to limit the movement trajectory of the ball head 721, so that the ball head 721 floats up and down or left and right along the opened cross groove 7201, so that the support head 72 can fit against the inclined surface of the object. The reset mechanism 76 connected to the movable column 71 at the head end presses the abutment ring 764 against the support head 72 under the action of the tension spring 765. When the support head 72 separates from the surface of the object, the tension spring 765 resets and corrects the inclined support head 72 through the abutment ring 764, improving the convenience of the support head 72 abutting against the object.
[0023] Working principle: A multi-axis robotic arm is used as the actuator. The support platform fixed to its end is symmetrically equipped with slidingly connected movable blocks 3. The movable blocks 3 are driven by hydraulic or pneumatic power, which can drive the fixed frame 4 to achieve the gathering or dispersing action. The hydraulic pump 6 configured at the top of the fixed frame 4 is used to regulate the oil pressure in the frame, while the flow-gathering hood 5 fixed to one end of the fixed frame 4 is connected to the external negative pressure equipment through the pipeline, forming a complete suction generation system. When the support platform 2 drives the fixed frame 4 to converge, the support head 72 inside the fixed frame 4 comes into contact with the surface of the object and moves towards the tail positioning post 73 by squeezing the head end movable column 71; the hydraulic pump 6 is started to pump the oil in the fixed frame 4 outward, so that the oil pressure in the frame increases, pushing the support head 72 connected to the head end movable column 71 to generate negative pressure suction; when the head end movable column 71 moves to the tail positioning post 73, the oil pressure achieves braking, thereby firmly adsorbing and fixing the object abutting the support head 72; this dual fixing mechanism effectively avoids the object slippage that may be caused by relying solely on friction, and significantly improves the limiting stability; The cylindrical structure built into the tail-end positioning post 73 is connected to the elastic oil bladder 77 and the flow chamber respectively. The piston block 742, which is movably connected inside the inner cylinder 731, passes through the cylinder wall and is fixedly connected to the head-end movable post 71. The oil pre-filled in the elastic oil bladder 77 is used to fill the space generated when the piston block 742 moves. When the piston block 742 moves away from the elastic oil bladder 77 along the inner cylinder 731, the oil in the inner cylinder 731 flows into the flow chamber through the guide hole 732, and then enters the piston cylinder 712 in the head-end movable post 71 through the connecting pipe. The hydraulic system is activated. After the pump 6 pressurizes the oil, the piston block 743 inside the piston cylinder 712 moves directionally along the support rod 741 under the action of the oil pressure. If the support head 72 forms a sealed structure with the surface of the object, the movement of the piston block 743 will generate negative pressure at the support head 72, achieving adsorption and fixation. If no sealed structure is formed, the piston block 743 moves to the limiting tube, making the flow chamber and the inner cylinder 731 sealed. At the same time, the block triggers the air guide tube to connect the support head 72 and the flow hood 5, generating suction through the external negative pressure device, thus achieving stable fixation of the object.
[0024] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A robotic arm with an adaptive mechanical positioning fixture, characterized in that, Includes a robotic arm (1) and a support platform (2); The support platform (2) is symmetrically provided with movable blocks (3) at one end, and a fixed frame (4) is fixedly connected to one end of the movable block (3). A hydraulic pump (6) is provided at the top of the fixed frame (4), and a flow-concentrating hood (5) is provided at one end of the fixed frame (4). It also includes a support member (7), which consists of a head movable column (71), a support head (72) and a tail positioning column (73). The head movable column (71) is slidably connected to the fixed frame (4), and the tail positioning column (73) is located inside the fixed frame (4). A connecting member (74) is provided between the tail positioning column (73) and the head movable column (71). When the support head (72) is pressed against the object, the fixed frame (4) fixed to the movable block (3) is driven by the support platform (2) to converge. The support head (72) is forced to move the movable column (71) at the head end to the positioning column (73) at the tail end through the linkage (74). The hydraulic pump (6) drives the oil in the fixed frame (4) to move, so that the positioning column (73) at the tail end locks the movable column (71) at the head end and the object is adsorbed and fixed by the support head (72).
2. The robotic arm with an adaptive mechanical positioning fixture according to claim 1, characterized in that, An inner tube (731) is fixedly connected inside the tail end positioning post (73), and a flow cavity is provided between the inner tube (731) and the tail end positioning post (73). A guide hole (732) is symmetrically provided at one end of the inner tube (731), and the guide hole (732) connects the inner tube (731) and the flow cavity.
3. The robotic arm with an adaptive mechanical positioning fixture according to claim 1, characterized in that, One end of the tail-end positioning post (73) is fixedly connected to an elastic oil bladder (77), and the elastic oil bladder (77) is connected to the inner cylinder (731). A connecting tube (733) is movably provided at one end of the tail-end positioning post (73) near the elastic oil bladder (77). One end of the connecting tube (733) passes through the tail-end positioning post (73) and is connected to the flow cavity. The other end of the connecting tube (733) is fixedly connected to a head-end movable post (71).
4. A robotic arm with an adaptive mechanical positioning fixture according to claim 3, characterized in that, The connecting pipe (733) is fixedly connected to a retaining ring (7332) at one end near the head end movable column (71), and the retaining ring (7332) limits the connecting pipe (733) on the head end movable column (71). The connecting pipe (733) is fixedly connected to a limiting pipe (7331) at one end near the retaining ring (7332), and the limiting pipe (7331) is located inside the head end movable column (71).
5. A robotic arm with an adaptive mechanical positioning fixture according to claim 2, characterized in that, A piston block (742) is movably connected inside the built-in cylinder (731). A support rod (741) is fixedly connected to one end of the piston block (742). An air guide pipe (75) is provided inside the support rod (741). One end of the air guide pipe (75) is connected to the flow hood (5), and the other end of the air guide pipe (75) is connected to the head end movable column (71).
6. A robotic arm with an adaptive mechanical positioning fixture according to claim 2, characterized in that, A piston block (742) is movably connected inside the built-in cylinder (731). A support rod (741) is fixedly connected to one end of the piston block (742). An air guide pipe (75) is provided inside the support rod (741). One end of the air guide pipe (75) is connected to the flow hood (5), and the other end of the air guide pipe (75) is connected to the head end movable column (71).
7. A robotic arm with an adaptive mechanical positioning fixture according to claim 1, characterized in that, The piston cylinder (712) is equipped with a piston block two (743), which is slidably connected to the support rod (741). One end of the piston block two (743) is fixedly connected to the support rod (7431), and the other end of the support rod (7431) is fixedly connected to the stop block (7432).
8. A robotic arm with an adaptive mechanical positioning fixture according to claim 1, characterized in that, One end of the support head (72) is fixedly connected to a ball head (721), and the ball head (721) is adapted to the ball groove (714). A connecting groove (722) is opened in the support head (72) and the ball head (721), and the connecting groove (722) is connected to the ball groove (714).
9. A robotic arm with an adaptive mechanical positioning fixture according to claim 1, characterized in that, The head end movable column (71) has a directional slide groove (717) at one end near the locking block (711), and the directional slide groove (717) is slidably connected to a reset mechanism (76).
10. A robotic arm with an adaptive mechanical positioning fixture according to claim 9, characterized in that, The reset mechanism (76) includes a slide rod (762) and the slide rod (762) is adapted to a directional sliding. One end of the slide rod (762) is fixedly connected to a collar (761), one end of the collar (761) is fixedly connected to a tension spring (765), and the other end of the tension spring (765) is fixedly connected to a locking block (711). The other end of the slide rod (762) is fixedly connected to a fixing ring (763), one end of the fixing ring (763) is fixedly connected to a stop ring (764), and a support head (72) is provided inside the stop ring (764).