Whilst reviewing literature pertaining to current, non-industrial robotics (section 2.3 - 2.5), it appeared that there was a major lack of variability of educational robotic manipulators on the market, aimed at the secondary education level, seemingly indicating a potential market gap. Fixed arm configurations like DexTAR, Mover6 and Scorbot can be very useful at teaching robotic theory; however, these systems are limited to only provide educational content directly relating to that specific type of robotic arm and therefore cannot educate a user about the numerous types of arms popular for industrial use. Throughout the mainstream industrial robotics industry, the type of robotic arm in use generally falls into one of the following categories: Cartesian, SCARA, cylindrical, spherical or articulated (tab. 3 - 1). The Shell-Core structured manipulator concept presented in this research aims to provide a platform in which all mainstream arms may be constructed. This is achieved through the use of various linkages (shells) and two types of mechanical actuators, rotational and linear (cores) as shown in Table 3 - 2. The design and development of these unique shells and cores provide a good educational study basis relating to mainstream industrial robotic configurations. Unique relating features include their compact design, interchangeable nature, simple configuration and reconfiguration, plug and play accessibility and their ability to construct commonly used mainstream industrial robotic manipulators. Tables 3 - 3 and 3 - 4 present some of the industrial robotic arms constructed using the Shell-Core concept.
Cartesian SCARA Cylindrical Spherical (Polar) Articulated
3 linear 2 rotational 1 linear 1 rotational 2 linear 2 rotational 1 linear 3+ rotational
Rotational (revolute) Linear (prismatic)
Table 3 - 2. Basic types of actuator.
Cartesian SCARA Cylindrical Spherical (Polar) Articulated
Table 3 - 3. Configurations realised with the proposed system (no end-effector).
PUMA (no gripper, no final axis)
SCARA (no linear, no
gripper) Articulated (with gripper)
Table 3 - 4. Other configurations.
3.1.1 Actuators Design
As defined in the kinematics section (tab. 2 - 18), each core unit will enable either rotational actuation or linear actuation in a single plane (fig. 3 - 1). One end of each core will be stationary with respect to the connected structural element, with both ends held in place by locating mounts. Due to the nature of inter-connecting, modular design, each core unit has its own on-board control electronics as well as pass along both data and power to the next core unit in the queue.
Each core unit has a unique ID and will be able to detect its position in the queue constructing the robotic arm. The queue position information, added with structural link type information, allows for complete knowledge of the assembled manipulator.
Figure 3 - 1. Actuator planes of motion.
Mechanical stops are implemented for the rotational actuator in a cam design, which limits its rotational range to less than 360°. This allows for a simplified homing methodology as well as preventing infinite rotation, reducing the overall complexity needed for power and data transmission.
The amount of actuation required from each core unit making up the manipulator arm may not be equal. Because of this, more power is needed of the rotational actuator at the base of the robot, resulting in components with varying power outputs. Hence two types of actuators are included, self-locking and non-self-locking.
Passive building blocks are designed to the same size and dimensions as a rotational or linear actuation unit, however, this unit will not allow for any movement whatsoever. Power and data lines are supported. The purpose of this component is to increase the variety of useable robotic building blocks, which in turn will accommodate for different assembly of robotic arms, such as the cylindrical configuration (fig. 3 - 2).
3.1.2 Shell Structural Units
Shell structural units as shown in Figure 3-5 are specifically designed to make the assembly of a robotic arm possible. The goals of these shells are to inter-connect actuators and provide appropriate offsets for mechanical motion in various planes in different robot arm configurations.
Each shell structural unit has a unique ID attached to its specific dimensions, which are passed along and recognised by a pre-programmed microcontroller, allowing it to act accordingly. This information is also sent to the master control unit which may in turn adjust system kinematics to suit the specific arrangement. Upon installation the ‘Structure type’ is configured to correspond with the correct robot arm structure.
Power and data will be conveyed through the structural piece itself.
Figure 3 - 3. Shell Structural Units.
3.1.3 End-Effectors
As the nature of the system is modular, the end-of-arm tooling platform is flexible and permits any appropriate design requiring power and data exclusively. Varying end- effectors will also be included depending on application, eg: electro-magnetic, 2-fingered gripper, 3-fingered gripper, drawing utensil attachment.
The 2-fingered electronic gripper will be the first addition to the eventual range of grippers accompanying this system. The unit will be a separate component, supporting the plug-and-play feature as the other modules in the system. The 2-fingered gripper may also introduce another rotational axis, providing actuation directly to the handled part; in addition, this will simplify the configuration of some robotic manipulators, such as the PUMA (fig. 3 - 4).
Figure 3 - 4. 2-Fingered gripper pictures.
Figure 3 - 5. PUMA realised with gripper addition.