ORA

ORA is a plug-and-play robotic arm built with six industrial actuators on each of its six joints, providing six degrees of freedom along six axes of movement (X, Y, Z & Pitch, Roll, Yaw).

ORA is designed and engineered for education. It is designed to take up minimal space while still providing a safe working distance of 440 mm in any direction horizontally and over 680 mm vertically. ORA is designed with safety in mind, including collision detection and an emergency stop button.

ORA can be programmed with the latest version of Ozobot Blockly. The programming environment offers blocks (controls) that allow the user to program ORA’s movements more freely along its six axes and degrees of freedom. The programming environment also allows you to utilize the ORA grid system that is incorporated into the included mat. The grid system is a simplified offering for beginners to learn how ORA moves through a 3D space along its six axes using predefined locations integrated into specific programming blocks.

Parts of the Arm

See the images in the student section.

1. Base
2. Joint 1
3. Joint 2
4. Joint 3
5. Joint 4
6. Joint 5
7. Joint 6
8. Pneumatic Gripper
9. Vacuum Gripper
10. Emergency Stop Button
11. Power Supply

Emergency Stop

The emergency stop button sends a command to cut off power between the power supply and the robotic arm. Pressing it will immediately shut down ORA and stop any of its movements.

If for any reason you feel the arm may cause harm to you, to others, to the table, or to anything else in the vicinity, press the emergency stop button immediately.

To reset the emergency stop button, twist the button clockwise until it releases upward.

Understanding the Six Axes

ORA is capable of moving along each of the X, Y, and Z axes. The X axis controls ORA’s forward and backward movements. The Y axis controls its left and right movements. The Z axis controls ORA’s movements up and down. Any movement along each of the different axes is called translation.

Notice that the base and tool head have Z axes that move in opposite directions. An upward movement of the tool head along its Z axis would move it closer to the table, while an upward movement of the tool head along the Z axis of the base would move it further away from the table.

ORA’s six joints allow it to also turn along the Pitch (P), Roll (R), and Yaw (Y) axes. Any movement along each of these different axes is known as rotation.

Rotation around the front-to-back axis (X) is called Roll. Rotation around the side-to-side axis (Y) is called Pitch. Rotation around the vertical axis (Z) is called Yaw.

Six Degrees of Freedom

The six degrees of freedom (6DOF) is a representation of how an object moves through 3D space by either translating linearly or rotating axially. A single degree of freedom on an object is controlled by the up/down (Z), forward/back (X), left/right (Y), pitch, roll, or yaw.

Six Degrees of Freedom - Translation

Three of the 6DOF are controlled through translation. As you recall, a translation is any movement along the X, Y, and Z axes. A linear translation’s degrees of freedom are controlled by defining the origin (like the base or the tool head of the robotic arm) and should all be perpendicular to one another respectively.

Translation does not affect an object’s rotation. In theory, the object could be rotating in space and not have any translation, like a wheel spinning on a stationary axle.

Six Degrees of Freedom - Rotation

The remaining three 6DOF are controlled through axial rotation. Typically, the three rotational degrees of freedom, Pitch (P), Roll (R), and Yaw (Y), will rotate around the center of the object’s origin. The rotational degrees of freedom are controlled by either a level plane or by a line. Similar to the three linear translation degrees of freedom, the rotational degrees of freedom are perpendicular to one another. The rotational degrees of freedom will be considered at the center axis of the linear degrees of freedom. XYZ linearly are respective to PRY rotationally.

Movement & Rotation Limits

ORA, like most robotic arms, has limits on how far it can safely extend or rotate. It is important to keep these limits in mind when programming ORA.

• With the tool head pointing down and the arm fully extended, ORA can rotate 880 mm around the base.
• With the tool head parallel to the table and the arm fully extended, the tool center point (TCP) can reach over 680mm.

Each joint can move independently and in conjunction with the others. Some of the joints are designed to provide full 360º of rotation in either direction (J1, J4, J6), while others are limited due to interference with other parts of the robotic arm (J2, J3, J5). Each axial rotation limit is listed below:

• J1 (±360°)
• J2 (±150°)
• J3 (-3.5°~300°)
• J4 (±360°)
• J5 (±124°)
• J6 (±360°)

Collisions

Collisions can occur for various reasons. Most are a result of the arm trying to move beyond its limits.

Some specific examples include:

• If ORA detects a change in the amount of torque used by a joint that exceeds a normal range during the movement, the robotic arm will automatically stop to prevent damage to the arm itself and/or any injury to the operator.
• If ORA collides with itself or another object/surface during the movement that results in an automatic stop, it will report an error that must be cleared before it can be used normally. Be sure to clear any obstructions and refactor your code to avoid any further collisions.

While the ORA grid system providews simplified offering of codeable movements, when it finds itself in certain positions, the robotic arm’s linear motion may be impeded. The chart below shows how the arm moves from location to location when starting from the initial position. The light blue squares denote locations that require at least one additional move before the arm can safely get there. The green squares show pairs of locations that the arm can move directly and safely from one to the other when starting from the initial position. And the red squares indicate pairs of locations that require and intermediate location when moving from one to the other.

These collisions occur when the arm attempts to pass through the center of a plane in which a part of ORA exists. The primary example for this is when the arm has to pass through the center of the grid, thus causing a collision between a part of the arm and the base.

Singularity

Singularities occur when the axes of any two joints of a robotic arm are on the same straight line (see image). At the singularity point, the robot's degrees of freedom will be degraded. This causes the angular velocity of some joints to be too fast and can lead to a loss of control. One common occurrence is when the wrist joint (J5) is at or near the axis of the first joint (J1). When this happens, a singularity point appears. To avoid a loss of control (likely to cause J1 to move too fast), the robotic arm should keep from passing directly over or through the center area of the base.

A characteristic of a singularity is when a planned movement cannot be performed correctly. For example, a coordinate-based movement cannot be explicitly translated into joint rotations of each axis. So when the arm attempts to perform a motion (excluding joint movements) near a singularity point, it will stop itself to avoid an instantaneous increase of speed at the joint that would pass the singularity point. Be sure that the rotation of the joint does not move near a singularity point or try to avoid them all together.

Grippers

Pneumatic Gripper

• The pneumatic gripper is an end-effector of the robotic arm that can grasp objects dynamically.
• Using the provided tool, you can unscrew the four screws holding in the mechanical claw and position them in one of two ways.
• The normal installation provides a stroke range of 0-16mm (image 2), and the reverse installation provides a stroke range of 20-38mm (image 1). Regardless of the installation method, the maximum stroke of the gripper is 16mm.
• The maximum payload of the gripper is 600g.
• The two states of the gripper are open and closed (on or off in Ozobot Blockly).

Vacuum Gripper

• The vacuum gripper is able to create a constant suction on a smooth object that doesn’t exceed 600 g.
• The vacuum gripper can be equipped with one of three suction cups. The size, weight, and surface of an object can determine wich size suction to use.
• If the surface of the object is not smooth, the suction cup may not be able to create a sealed connection, resulting in an air leakage and a failed attempt to raise or move the object.

Precautions

• When ORA is equipped with one of the two grippers, the arm’s trajectory changes and it is necessary to perform a safety assessment. You must take into account how ORA will move, rotate, and return to various points to avoid collisions.

ORA Grid System

The included table mat intrudoces the ORA Grid System. As mentioned previously, the grid system grid system is a simplified approach to learning how ORA can move through a 3D space along its linear axes (XYZ) using non-complex, pre-defined locations that are all integrated into a handful of easy-to-use programming blocks. This system makes it easy for beginners to be accurate and efficient right from the start.

In Lesson 2, you will learn all about each of these blocks, including how they work and how you can use them to program ORA.

Other key features of the mat and ORA Grid System include:

• Markings for X (red) and Y (green) axes.
• Markings (dashed circle with a center point) for accurate placement of Evo or other objects. The exact location of each marking is part of the pre-programming included in the blocks above.
• A calibration circle for anyone using Evo to line follow in conjunction with ORA.