6-axis Robot Arm V760 Ver.2

Started: November 2019 Completed: December 2019 Released: January 2020 The robotic arm, which I built in 2015, has been reworked to version 2. The article on version 1 can be found here. The following changes have been made: V760 is the name I have given to the model. Note that there is no product by this name. I made the exterior panel as long as it could be without it becoming too heavy. The pivot axis (Joint 1) has been made more compact. The appearance gives the impression of the basic bricks being stacked. However, it is reinforced from within by liftarms, which keep it from uncoupling. The motor of Joint 2 is centered. The deceleration mechanism of the 6th axis has been modified. The planetary reduction gear that uses the internal gear of the 56-tooth turntable has been modified into a combination of the 60-tooth turntable and the 12-tooth bevel gear. Since the 60-tooth turntable was introduced, it appears the 56-tooth turntable is no longer available in the official Lego set. Hence, I am going to be using the 60-tooth turntable as much as possible in my future designs. I changed the cables to thin Mindsensors cables, and this is the only component of this robot that is not a genuine Lego product. However, there are no lengthy genuine Lego cables, making it unavoidable. I am still improving the program: working on multiple issues, which I would like to fix. For example, synchronization between the two EV3s is currently achieved using a set of optical sensors. I have tried using serial communication (UART) but gave up because I could not solve the problem of EV3 freezing in the middle and communication subsequently getting cut off. A video demo of the GBC module using the robot can be found here.

6-Axis Robot Arm (Type: V760)

Started: November 2015 Completed: December 2015 Released: December 2015 6-Axis Robot Arm (Type: V760) using Lego Mindstorms EV3.
V760 is an improved model of the 5-Axis Robot Arm (S750) using NXT. The degree of freedom of S750 was five, so that the hand posture of S750 at an arbitrary position was restricted. The degree of freedom V760 is improved to be six, so the hand of V760 can move to an arbitrary position with any posture. The structure of the joints of V760 is the same as a general industrial 6-axis vertical articulated robot. bP1000259mbP1000264m I aimed to make the shape of the robot slim. The robot V760 is easy to build in a smaller size because new Lego parts such as medium-sized servo motors and 60-tooth turntables are available. The spring balancer is used only at the second joint that is subjected to the heavy duty. I always try to build my Lego models only using genuine Lego parts, but for V760 I used long cables (70 and 90 cm) made by HiTechnic Co., Ltd. because a genuine Lego cable (50 cm) is too short to connect. bP1000228mbP1000186m I had difficulty in making the turning bearing of V760. It is subjected to large bending moment when the arm takes a horizontal posture. It is difficult to bear the moment only by a single turntable part. In order to solve the problem, I added a bearing that is consist of 4X4 size macaroni parts and roller parts in addition to a regular bearing made from a turntable part. A pair of bearings disperse the stress caused by bending moment. The structure achieves both of the strength against large moment and the slim shape of the hip of the robot. The programs executed in EV3 bricks are written in C using TOPPERS/EV3RT. Though I wanted to use USB or Bluetooth for the communication between two EV3 bricks, the communication has not been achieved yet. I temporary used two light sensors to enable two EV3 bricks to communicate with each other by synchronizing signal. The EV3 bricks calculate the inverse kinematics of the robot in real time and solve the angle of the each joint from the target position and posture of the hand. In the demo video, the movement from a start position to a target position is calculated in different two modes. In the linear interpolation mode, the movement of the hand draws a linear locus. In the joint interpolation mode, the movement of the hand does not draw a linear locus. Not EV3 L-motor but NXT motor is used for rotating the second joint because the inner gear backlash of NXT motor is smaller than that of EV3 L-motor. I am planning to attach a chuck at the tip of the robot and the robot can be used for material handling.