High-rigidity heavy-load robot with closed-loop structure

Abstract

The invention relates to a robot, in particular to a high-rigidity heavy-load robot with a closed-loop structure. The invention aims to provide a high-rigidity heavy-load robot with a closed-loop structure. The robot has the characteristics of high rigidity, high precision and the like. According to the technical scheme, the invention provides a high-rigidity heavy-load robot with a closed-loop structure. The robot is characterized by further comprising a base fixed to the ground, a rotating base capable of rotating around the vertical axis and being positioned at the top end of the base, a first driving device installed in the rotating base and used for driving the rotating base to rotate, and a first mechanical arm capable of swinging around the horizontal axis and being positioned on the rotating base; the second driving device is installed on the rotating base to drive the first mechanical arm to swing, and the second mechanical arm is connected to the top end of the first mechanical arm through a hinge shaft. The third driving device is mounted on the rotating base to drive the second mechanical arm to swing; and the two sets of hydraulic rods are mounted between the rotating base and the first mechanical arm and used for balancing torque.

Description

Technical Field

[0001] The invention relates to a robot, in particular to a high-rigidity heavy-load robot with a closed-loop structure. Background Art

[0002] High-rigidity heavy-duty robots have shown extremely important application value in many fields. In the manufacturing industry, such as automobile manufacturing, heavy automobile parts such as engines and frames need to be moved during the assembly of automobile bodies. For these heavy parts, only robots with heavy-duty load capacity can ensure that these heavy parts are accurately moved and positioned to the correct position. In automobile body welding, high-rigidity robots can reduce vibration and deformation during welding, making the welding trajectory more accurate, thereby improving welding quality and ensuring the structural strength of the automobile body. In the field of port logistics, a large number of containers need to be moved. For container loading and unloading operations, high-rigidity heavy-duty robots are generally used to improve the loading and unloading efficiency of ports. Compared with traditional cranes, high-rigidity heavy-duty robots are more flexible and more automated, and high rigidity can ensure that the robot can effectively prevent the container from shaking in the complex environment of the seaside under the influence of factors such as sea breeze, ensuring the safety and accuracy of cargo loading and unloading. In the field of construction, robots need to carry heavier inspection equipment for inspection and maintenance of building structures. Heavy-load capacity ensures that robots can move these inspection equipment to various parts of the building structure, and high rigidity helps robots maintain stability at high altitudes and on complex building surfaces. Robots with high rigidity and heavy-load performance improve production efficiency and quality, and reduce production costs and risks. With the continuous advancement and innovation of technology, the application prospects in these fields will be broader.

[0003] For traditional open-loop heavy-duty robots, due to their open-loop structure, when the load is large, the open-loop structure is more likely to accumulate end errors, resulting in low working accuracy. Due to the structural characteristics of the open-loop structure, the final load is borne by the end branch chain alone, and the torque is transmitted by a single connecting rod, which makes the overall load-bearing capacity and deformation resistance of the robot low. Therefore, the load capacity and stiffness of the robot with an open-loop structure are relatively low, so it is necessary to introduce a robot with a closed-loop structure. For heavy-duty robots with closed-loop structures, the advantages are particularly obvious compared to traditional open-loop structures. Multiple branches in the closed-loop structure bear the load at the same time, and its structure has better load-bearing capacity and greater deformation resistance; and due to the structural characteristics, the working accuracy is higher. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and provide a high-rigidity heavy-load robot with a closed-loop structure, which has the characteristics of high rigidity and high precision.

[0005] In order to achieve the above purpose, the technical solution provided by the present invention is:

[0006] A high-rigidity heavy-load robot with a closed-loop structure includes an end working flange or a working arm with three degrees of freedom; the characteristic is that the robot also includes a base fixed to the ground, a rotating base rotatably positioned at the top of the base around a vertical axis, a first driving device installed in the rotating base to drive the rotating base to rotate, a first mechanical arm positioned on the rotating base so as to swing around a horizontal axis, a second driving device installed on the rotating base to drive the first mechanical arm to swing, a second mechanical arm connected to the top of the first mechanical arm through a hinge shaft, a third driving device installed on the rotating base to drive the second mechanical arm to swing, and two sets of hydraulic rods installed between the rotating base and the first mechanical arm for balancing torque; the second mechanical arm is installed with the end working flange or the working arm.

[0007] The bottom end of the first mechanical arm is swingably positioned on the rotating base through a second rotating pair; the second rotating pair includes a connecting shaft horizontally arranged and fixed to the bottom end of the first mechanical arm, and a sleeve installed on the rotating base and rotatingly matched with the connecting shaft.

[0008] The hydraulic cylinders of the two sets of hydraulic rods are swingably positioned on both sides of the rotating base through the fourth rotating pair, and the movable rods matched with the hydraulic cylinders are connected to the top end of the swing arm through the fifth rotating pair; the bottom end of the swing arm is fixed to the connecting shaft.

[0009] The fourth rotating pair includes an articulated sleeve fixed to the hydraulic cylinder and an articulated shaft fixed to the rotating base and rotatably matched with the articulated sleeve; the articulated shaft is horizontally installed on the rotating base, and both ends of the articulated shaft extend outward on the left and right sides of the rotating base, thereby being articulated with the articulated sleeve.

[0010] The fifth rotation pair comprises a short shaft fixed to the swing arm and an articulated cylinder fixed to one end of the movable rod and rotatably matched with the short shaft; the rotation axes of the two fifth rotation pairs are coaxially arranged.

[0011] The second driving device includes a first moving pair installed on a rotating base, a first screw pair and a second motor driving the first moving pair; the first moving pair includes a first guide rail installed horizontally on the rotating base and perpendicular to the rotating axis of the second rotating pair, and a first slider matched with the first guide rail; the first screw pair includes a first screw installed on the rotating base and parallel to the first guide rail, and a first screw nut matched with the first guide rail and connected to the first slider; one end of the first driving rod is hinged to the first mechanical arm, and the other end is hinged to the first slider; the motor shaft of the second motor is connected to the first screw through a coupling.

[0012] The third driving device includes a third motor installed on the third driving device mounting seat and driving the second moving pair through the second screw pair; the second moving pair includes a second guide rail installed horizontally on the third driving device mounting seat and perpendicular to the rotation axis of the second rotating pair, and a second slider matched with the second guide rail; the second screw pair includes a second screw installed on the third driving device mounting seat and parallel to the second guide rail, and a second screw nut matched with the second guide rail and connected to the second slider; one end of the second driving rod is hinged to the second mechanical arm, and the other end is hinged to the second slider; the motor shaft of the second motor is connected to the second screw through a coupling.

[0013] One end of the second robotic arm is connected to the top of the first robotic arm through the third rotating pair, and the other end is connected to the second driving rod in the third driving device through the ninth rotating pair, and the other end of the second driving rod is connected to the second slider through the eighth rotating pair; the third rotating pair, the ninth rotating pair and the eighth rotating pair all include a rotating shaft arranged horizontally and parallel to the rotating axis of the second rotating pair, and a bushing matching the rotating shaft.

[0014] The rotating base can be rotatably positioned around a vertical axis at the top of the base through a first rotating pair, and the first rotating pair includes a circular guide rail laid on the top of the base and a plurality of sliders installed at the bottom of the rotating base and cooperating with the circular guide rail; the first driving device includes two first motors symmetrically installed on the bottom plate of the base, two first gears installed one by one on the two first motor shafts, and a second gear fixed at the bottom end of the base and simultaneously meshing with the two first gears.

[0015] The three-degree-of-freedom working arm includes a third robotic arm rotatably positioned on the second robotic arm, a motor and a transmission gear set installed on the second robotic arm for driving the third robotic arm, a fourth motor mounting base rotatably positioned at the top of the third robotic arm, a fourth motor installed in the fourth motor mounting base, and an end working flange connected to the end of the fourth motor shaft.

[0016] The beneficial effects of the present invention are:

[0017] The high-rigidity heavy-load robot with a closed-loop structure proposed in the present invention has the characteristics of high stability, high rigidity, and high load capacity, and can be applied to multiple fields such as manufacturing, logistics, and construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the three-dimensional structure of Example 1 of the present invention.

[0019] Figure 2 This is a schematic diagram of the structure of the first driving device in Example 1 of the present invention.

[0020] Figure 3Schematic diagram of driving the second driving device in Example 1 of the present invention.

[0021] Figure 4 This is a driving schematic diagram of the third driving device in Example 1 of the present invention.

[0022] Figure 5 This is Example 2 of the present invention.

[0023] Reference numerals:

[0024] 1-base, 1.1-bottom plate, 1.2-first motor base, 1.3-first motor, 1.4-first gear, 1.5-second gear, 1.6-gear connecting base, A1-first rotating pair;

[0025] 2-rotation base, 2.1-fourth rotation pair mounting seat, A2-second rotation pair;

[0026] 3-second driving device, 3.1-first slider, 3.2-first guide rail, 3.3-first lead screw, 3.4-second motor seat, 3.6-second motor, 3.7-first driving rod, A3-third rotating pair;

[0027] 4-first mechanical arm, 4.1-connecting shaft, 4.2-swing arm, 4.3-seventh rotation pair mounting seat, A4-fourth rotation pair;

[0028] 5-third drive device mounting seat, A5-fifth rotation pair;

[0029] 6-third driving device, 6.1-second slider, 6.2-second guide rail, 6.3-second lead screw, 6.4-second coupling, 6.5-third motor, 6.6-third motor seat, 6.7-second driving rod, A6-sixth rotating pair;

[0030] 7-second mechanical arm, 8-third mechanical arm, 9-fourth motor mounting seat, 10-first motor, 11-end working flange, 12-hydraulic rod;

[0031] A7-the seventh rotation pair, A8-the eighth rotation pair, A9-the ninth rotation pair, A10-the tenth rotation pair, A11-the eleventh rotation pair. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the examples shown in the accompanying drawings.

[0033] Example 1

[0034] Figure 1In the high-rigidity heavy-load robot with a closed-loop structure shown, a base 1 is fixed to the ground, a rotating base 2 is rotatably mounted on the top of the base around a vertical axis via a first rotating pair A1, the base bears the gravity of the rotating base and the mechanisms carried thereon via the first rotating pair, and a first driving device is mounted in the base to drive the rotating base to rotate.

[0035] The second driving device 3 is horizontally installed on the rotating base, and the first robot arm 4 is installed on the rotating base through the second rotating pair A2. The second driving device drives the first moving pair to rotate the first robot arm 4 around the axis of the second rotating pair A2; in order to prevent the robot from having accuracy deviation due to excessive load on the working end, two sets of hydraulic rods 12 are respectively installed on both sides of the rotating base and the first robot arm to balance the torque.

[0036] A third driving device 6 is installed on the third driving device mounting seat 5 above the second driving device, and is positioned at a rearward position relative to the upper part of the second driving device; both ends of the second robotic arm 7 are respectively connected to the first robotic arm through the third rotating pair A3 and the ninth rotating pair A9 and the third driving device, and the third driving device drives the second moving pair to move so that the second robotic arm rotates around the third rotating pair.

[0037] Figure 2 The specific structure of the first driving device; wherein: the top of the base 1 is circular, and a circular guide rail is laid on the top of the base. The rotating base is rotatably positioned at the top of the base 1 through a plurality of sliders fixed at its bottom end and matched with the circular guide rail, and is arranged coaxially with the base; obviously, the circular guide rail and the plurality of sliders form the first rotating pair. The middle part of the bottom of the rotating base is fixed with a gear connecting seat 1-6, and the second gear 1.5 is fixed at the bottom of the gear connecting seat and arranged coaxially with the base. Inside the base, two first motor mounting seats 1.2 are symmetrically mounted on the bottom plate 1.1 of the base, and two first motors 1.3 are respectively mounted in two motor seats. The motor shafts at the top of the two motors are arranged vertically upward and fixed with the first gears 1.4 respectively, and the two first gears are meshed with the second gears at the same time. When working, the two motors drive the two first gears respectively, and the gear connecting seat and the rotating base can be driven to rotate together by transmitting the second gear.

[0038] Figure 3It is a driving schematic diagram of the second driving device and the first mechanical arm; wherein: in the second driving device 3: the first slider 3.1 and the first guide rail 3.2 cooperate to form a first moving pair, and the first guide rail is horizontally installed on the rotating base; the first lead screw 3.3 is rotatably installed on the first guide rail seat through brackets at both ends, and is arranged parallel to the first guide rail; the length direction of the first guide rail is perpendicular to the second rotating pair; the second motor seat 3.4 is installed at the end of the first guide rail (the end away from the first mechanical arm), the second motor 3.6 is installed in the second motor seat, and the second motor shaft is connected to the first lead screw through a coupling; the first lead screw nut meshing with the first lead screw is also fixed on the first slider that slides on the first guide rail.

[0039] One end of the first mechanical arm is hinged to the shaft sleeve on the rotating base through a horizontally arranged connecting shaft 4.1, and the connecting shaft 4.1 is fixed to the bottom end of the first mechanical arm; the connecting shaft extends outward from both ends, and the two ends are respectively installed with swing arms 4.2, and the other ends of the two swing arms are respectively connected to one end of the movable rod in two sets of hydraulic rods (the hydraulic rods include hydraulic cylinders and movable rods that cooperate with the hydraulic cylinders through pistons) through the fifth rotation pair A5, and the hydraulic cylinders of the two sets of hydraulic rods are installed on both sides of the rotating base through two fourth rotation pairs A4. The fifth rotation pair A5 is composed of a short shaft fixed to the swing arm and a hinged cylinder fixed to one end of the movable rod and rotatingly cooperated with the short shaft; the rotation axes of the two fifth rotation pairs A5 are coaxially arranged. The fourth rotation pair A4 is composed of an articulated sleeve fixed to the hydraulic cylinder, and an articulated shaft fixed to the rotating base and rotating with the articulated sleeve; the articulated shaft is installed on the rotating base through the fourth rotation pair mounting base 2.1 on the left and right sides of the rotating base, and both ends of the articulated shaft extend outward on the left and right sides of the rotating base to rotate with the articulated sleeve. The oil circuits of the two sets of hydraulic rods are independent and adjusted to the same oil pressure, which can ensure the torque balance of the two first mechanical arms during operation.

[0040] The seventh rotation pair mounting seat 4.3 is fixed at the lower position of the first mechanical arm facing the second driving device 3; this mounting seat is hinged to one end of the first driving rod 3.7 in the second driving device (the seventh rotation pair mounting seat 4.3 cooperates with one end of the first driving rod 3.7 to form the seventh rotation pair). The other end of the first driving rod is hinged to the first slider 3.3 in the second driving device (the other end of the first driving rod cooperates with the first slider 3.3 to form the sixth rotation pair). Therefore, the movement of the first slider in the second driving device can drive the first mechanical arm to swing through the sixth rotation pair A6, the first driving rod 3.7 and the seventh rotation pair A7 in sequence.

[0041] Figure 4The diagram shows the driving of the third driving device 6 and the second mechanical arm; the third driving device 6 is installed on the rotating base through the third driving device mounting seat 5; the structure and connection relationship of the third driving device are similar to those of the second driving device, wherein: the second slider 6.1 and the second guide rail 6.2 cooperate to form a second moving pair, and the second guide rail is horizontally installed on the second driving device mounting seat; the second lead screw 6.3 is rotatably installed on the second guide rail seat through brackets at both ends, and is arranged parallel to the second guide rail; the third motor 6.5 is installed at the end of the second guide rail seat (the end away from the first mechanical arm) through the third motor seat 6.6, and the third motor is connected to the second lead screw through the second coupling; the second slider 6.1 that slidably cooperates with the second guide rail seat is also fixed with a second lead screw nut that meshes with the second lead screw, and the second slider is also connected to the second mechanical arm through the second driving rod 6.7.

[0042] One end of the second mechanical arm 7 is hinged to the other end of the first mechanical arm through a horizontally arranged rotating shaft (forming a third rotation pair A3), and the other end of the second mechanical arm is also hinged to the second driving rod 6.7 in the third driving device 6 through a horizontally arranged rotating shaft (forming a ninth rotation pair A9), and the other end of the second driving rod is hinged to the second slider in the third driving device through a hinge shaft (forming an eighth rotation pair A8); the second guide rail is horizontally installed above the mounting seat of the third driving device and its length direction is perpendicular to the third rotation pair.

[0043] The first guide rail of the second drive device and the second guide rail of the third drive device are parallel to each other. In order to expand the working angle of the flange and prevent interference with the movement of the first drive rod, the third drive device is installed further back than the second drive device (i.e., farther away from the first robotic arm).

[0044] The end working flange is installed on the second mechanical arm. The driving device drives the second mechanical arm to move, thereby driving the flange to move.

[0045] Figure 1 The rotation axis of the second rotation pair and the rotation axis of the third rotation pair are parallel to each other and arranged horizontally, and are perpendicular to the rotation axis of the first rotation pair. The rotation axis of the first rotation pair is arranged vertically.

[0046] Figure 3 The rotation axes of the fourth rotating pair, the fifth rotating pair, the sixth rotating pair, and the seventh rotating pair are parallel to the rotation axis of the second rotating pair and are perpendicular to the first guide rail seat axis of the first moving pair.

[0047] Figure 4 The rotation axis of the eighth rotation pair and the rotation axis of the ninth rotation pair are parallel to each other.

[0048] The first robotic arm, the second robotic arm, the third drive device, the third drive device mounting base and the rotating base constitute a closed-loop structure, and the second drive device, the first robotic arm and the rotating base also constitute a closed-loop structure, which greatly improves the overall rigidity and heavy-load performance of the robot.

[0049] The high-rigidity heavy-load robot with a closed-loop structure has three sets of drives. In the first drive device, the first motor drives the rotating base to rotate around the rotation axis of the first rotating pair through the gear set; in the second drive device, the second motor drives the first slider connected to the nut to move through the first lead screw, thereby driving the first mechanical arm to move around the rotation axis of the second rotating pair; in the third drive device, the third motor drives the second slider connected to the nut to move through the second lead screw, thereby driving the second mechanical arm to move around the rotation axis of the third rotating pair.

[0050] Example 2

[0051] like Figure 5 As shown, on the basis of the original overall structure, the flange on the original second mechanical arm is replaced with a working arm with three degrees of freedom. The specific structure is a third mechanical arm 8 rotatably positioned on the second mechanical arm, a motor and a transmission gear set (conventional structure, omitted in the drawing) mounted on the second mechanical arm for driving the third mechanical arm, a fourth motor mounting seat 9 rotatably positioned at the top of the third mechanical arm, a fourth motor 10 mounted in the fourth motor mounting seat, and an end flange 11 connected to the end of the fourth motor shaft. Obviously, the hinged structure between the bottom end of the third mechanical arm and the second mechanical arm forms the tenth rotation pair A10, and the hinged structure between the fourth motor mounting seat and the top end of the third mechanical arm forms the eleventh rotation pair A11.

[0052] Preferably, the axis of the tenth rotational pair is perpendicular to the axis of the third rotational pair and the length direction of the second robotic arm, and the axis of the eleventh rotational pair is perpendicular to the axis of the tenth rotational pair.

[0053] This working arm provides the robot with a pitch motion and two rotation motions, increasing the flexibility and functionality of the end of the robotic arm.

Claims

1. A high-rigidity heavy-load robot with a closed-loop structure, comprising a terminal working flange (11) or a working arm with three degrees of freedom; characterized in that: The robot also includes a base (1) fixed to the ground, a rotating base (2) positioned at the top of the base so as to be rotatable around a vertical axis, a first driving device installed in the rotating base to drive the rotating base to rotate, a first mechanical arm (4) positioned on the rotating base so as to be swingable around a horizontal axis, a second driving device (3) installed on the rotating base to drive the first mechanical arm to swing, a second mechanical arm (7) connected to the top of the first mechanical arm through a hinge shaft, a third driving device (6) installed on the rotating base to drive the second mechanical arm to swing, and two sets of hydraulic rods (12) installed between the rotating base and the first mechanical arm for balancing torque; the second mechanical arm is installed with the end working flange or the working arm.

2. The high-rigidity heavy-load robot with a closed-loop structure according to claim 1, characterized in that: The bottom end of the first mechanical arm is swingably positioned on the rotating base via a second rotating pair (A2), wherein the second rotating pair comprises a connecting shaft (4.1) arranged horizontally and fixed to the bottom end of the first mechanical arm, and a shaft sleeve mounted on the rotating base and rotatably matched with the connecting shaft.

3. The high-rigidity heavy-load robot with a closed-loop structure according to claim 2, characterized in that: The hydraulic cylinders of the two sets of hydraulic rods are swingably positioned on both sides of the rotating base through the fourth rotating pair (A4), and the movable rods matched with the hydraulic cylinders are connected to the top end of the swing arm (4.2) through the fifth rotating pair (A5); the bottom end of the swing arm is fixed to the connecting shaft.

4. The high-rigidity heavy-load robot with a closed-loop structure according to claim 3, characterized in that: The fourth rotating pair includes an articulated sleeve fixed to the hydraulic cylinder and an articulated shaft fixed to the rotating base and rotatably matched with the articulated sleeve; the articulated shaft is horizontally installed on the rotating base, and both ends of the articulated shaft extend outward on the left and right sides of the rotating base, thereby being articulated with the articulated sleeve.

5. The high-rigidity heavy-load robot with a closed-loop structure according to claim 4, characterized in that: The fifth rotation pair comprises a short shaft fixed to the swing arm and an articulated cylinder fixed to one end of the movable rod and rotatably matched with the short shaft; the rotation axes of the two fifth rotation pairs are coaxially arranged.

6. The high-rigidity heavy-load robot with a closed-loop structure according to claim 5, characterized in that: The second driving device comprises a first moving pair installed on a rotating base and articulated to a first mechanical arm, a first screw pair, and a second motor (3.6) driving the first moving pair; the first moving pair comprises a first guide rail (3.2) installed horizontally on the rotating base and perpendicular to the rotation axis of the second rotating pair, and a first slider (3.1) matched with the first guide rail; the first screw pair comprises a first screw (3.3) installed on the rotating base and parallel to the first guide rail, and a first screw nut matched with the first guide rail and connected to the first slider; one end of the first driving rod (3.7) is articulated to the first mechanical arm, and the other end is articulated to the first slider; the motor shaft of the second motor is connected to the first screw via a coupling.

7. The high-rigidity heavy-load robot with a closed-loop structure according to claim 6, characterized in that: The third drive device (6) comprises a third motor (6.5) mounted on the third drive device mounting seat (5) and driving the second movable pair through the second screw pair; the second movable pair comprises a second guide rail (6.2) mounted horizontally on the third drive device mounting seat and perpendicular to the rotation axis of the second rotating pair, and a second slider (6.1) matched with the second guide rail; the second screw pair comprises a second screw (6.3) mounted on the third drive device mounting seat and parallel to the second guide rail, and a second screw nut matched with the second guide rail and connected to the second slider; one end of the second drive rod (6.7) is hinged to the second mechanical arm, and the other end is hinged to the second slider; the motor shaft of the second motor is connected to the second screw via a coupling.

8. The high-rigidity heavy-load robot with a closed-loop structure according to claim 7, characterized in that: One end of the second mechanical arm (7) is connected to the top of the first mechanical arm through a third rotating pair (A3), and the other end is connected to the second driving rod (6.7) in the third driving device through a ninth rotating pair (A9), and the other end of the second driving rod is connected to the second sliding block through an eighth rotating pair (A8); the third rotating pair, the ninth rotating pair and the eighth rotating pair all include a rotating shaft arranged horizontally and parallel to the rotating axis of the second rotating pair, and a shaft sleeve matched with the rotating shaft.

9. The high-rigidity heavy-load robot with a closed-loop structure according to claim 8, characterized in that: The rotating base can be rotatably positioned on the top of the base around a vertical axis through a first rotating pair (A1), the first rotating pair comprising a circular guide rail laid on the top of the base and a plurality of sliders mounted on the bottom of the rotating base and cooperating with the circular guide rail; the first driving device comprises two first motors (1.3) symmetrically mounted on a base bottom plate (1.1), two first gears (1.4) mounted one by one on the two first motor shafts, and a second gear (1.5) fixed on the bottom of the base and simultaneously meshing with the two first gears.

10. The high-rigidity heavy-load robot with a closed-loop structure according to claim 9, characterized in that: The three-degree-of-freedom working arm comprises a third mechanical arm (8) rotatably positioned on a second mechanical arm, a motor and a transmission gear set mounted on the second mechanical arm for driving the third mechanical arm, a fourth motor mounting seat (9) rotatably positioned at the top end of the third mechanical arm, a fourth motor (10) mounted in the fourth motor mounting seat, and an end working flange connected to the shaft end of the fourth motor.

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