“I created an inovative laser engraver mashine with equipment available on my faculty. Because I was really pleased with the result I wanted to share the process and the final creation.
Fundamental principal of the device is quite inovative. Instead of a standard X-Y CNC machine programing and design, it uses two rotational movementf of two gears. For this to work, proper kinematic transformations have to be applied so that the inner coordinates of a device move the motors accordingly to the “world” coordinates. Only then can standard programing in XY coordinates be used for preparing vector images for engraving in software such as CadToMotion and others. Kinematic transformation that ensures proper transformation and applies also to this type of a device is primarily used for programing SCARA robots.
Mechanism uses two rotational movements; the first rotational axis moves the workpiece and the second axis moves the laser light source in the transverse direction. Although the motions along both axes are rotational and consequently nonlinear, the movement of the mechanism is in external coordinates, ie the Cartesian coordinate system and it’s performed with the help of kinematic transformation. Generation of motion trajectories, positional control of both servomotors and real-time calculation of kinematic transformation is performed with an industrial motion controller TRIO.
When planning the design of the mechanism the principles were: simple, innovative, efficient and easy to manufacture. Both axes are identical and made on the basis of a rotary plate with a diameter of 200 mm with external cycloid gearing (m = 0.3), which is driven by a servomotor via a second gear. To reduce the undesired effects of play and friction, the drive motor is mounted movably and the required contact force between the gears is determined by the coil spring pressure.
Motors
I used two DC servomotors from the manufacturer ESCAP type D2R 11 219P B 100Y. These are high-dynamic DC motors with permanent magnets and a rotor without an iron core. The motor operates in a closed loop system through which it receives information about the actual position by an encoder. The motors are connected to the output of a servo amplifier with 12 V power supply and their rated power is 15 W. The motors have a gear mounted on the shaft with a module m = 0.3 and have 19 teeth, which allows the transfer of power from the motor to a larger gear. An optical incremental encoder with 100 pulses per revolution is mounted on the motor shaft, through which the measurement of speed and position was performed.
Motion controller
An industrial motion controller is used to control the servo motors, with which we communicate via a personal computer in the MOTION PERFECT software tool. The controller has analog and digital inputs and outputs. Ethernet connection, motor (preliminary connection to the power supply), laser (with independent 5V power supply) are all connected to the controller.
Laser
The laser is connected to a switching power supply with an output voltage of 5V and a switching circuit is added, which switches on the laser beam with a signal from the digital output of the controller. The power of the laser is 1W and it’s wavelength is 405nm, which belongs to the visible spectrum of light and is perceived as the blue-purple color of the beam. Firstly the optimal focal length must be set, because only then the beam engraves the perfect line.
Gear
Two gears with a diameter of 206 mm and a thickness of 3 mm were used out of a lightweight material called Forex. A gear attached to the upper part of the structure has 624 teeth and a second one at the lower part has 629 teeth. Laser is attached to the upper gear and work surface to the lower gear. As the gears rotate, the laser engraves on the workpiece.
Bearings
Four IGUS polymer flange plain bearings, type FM-0608-08 were used. With them I mounted both large gears and two aluminum brackets for the servomotor. I used these bearings because they are easier to install and are comparable to classic ball bearings. Also, these bearings reduce the weight of the device itself.
Motor brackets
I designed two aluminum brackets for the motor. On one side there are holes for attaching the motor and on the other the bracket is mounted and attached to the housing. This method allows the motor to be pressed against the gear by a spring, which helps to effectively adjust the motor gear to any tolerances of the large gear. As a result, the teeth do not jump over each other and the wear of the gears is reduced.”