The delta robot is a parallel robot, i.e. it consists of multiple kinematic chains connecting the base with the end-effector. The robot can also be seen as a spatial generalisation of a four-bar linkage.[10]
The key concept of the delta robot is the use of parallelograms which restrict the movement of the end platform to pure translation, i.e. only movement in the X, Y or Z direction with no rotation.
The robot's base is mounted above the workspace and all the actuators are located on it. From the base, three middle jointed arms extend. The ends of these arms are connected to a small triangular platform. Actuation of the input links will move the triangular platform along the X, Y or Z direction. Actuation can be done with linear or rotational actuators, with or without reductions (direct drive).
Since the actuators are all located in the base, the arms can be made of a light composite material. As a result of this, the moving parts of the delta robot have a small inertia. This allows for very high speed and high accelerations. Having all the arms connected together to the end-effector increases the robot stiffness, but reduces its working volume.
The version developed by Reymond Clavel has four degrees of freedom:[6] three translations and one rotation. In this case a fourth leg extends from the base to the middle of the triangular platform giving to the end effector a fourth, rotational degree of freedom around the vertical axis.
Currently other versions of the delta robot have been developed:
Delta with 6 degrees of freedom: developed by the company Fanuc, on which a serial kinematic with 3 rotational degrees of freedom is placed on the end effector
Delta with 4 degrees of freedom: developed by the company Adept, which has 4 parallelogram directly connected to the end-platform instead of having a forth leg coming in the middle of the end-effector
Delta direct drive: a 3 degrees of freedom delta having the motor directly connected to the arms. Accelerations can be very high, from 30[11] up to 100 g.
Pocket Delta: developed by the company Asyril, a version of the delta Robot adapted for high-precision applications.
Delta Cube: developed by the LSRO, a delta robot built in a monolithic design, having flexure-hinges joints. This robot is adapted for ultra-high-precision applications.
Several "linear delta" arrangements have been developed where the motors drive linear actuators rather than rotating an arm. Such linear delta arrangements can have much larger working volumes than rotational delta arrangements.[12][13]
The majority of delta robots use rotary actuators. Vertical linear actuators have recently been used (using a linear delta design) to produce a novel design of 3D printer.[14][15] These offer advantages over conventional leadscrew-based 3D printers of quicker access to a larger build volume for a comparable investment in hardware.