They provide a low-cost, industrial-grade motion package with high accuracy using PBC Linear's patented Constant Force anti-backlash nut.
The dual xy actuators are specified for high rigidity, quick change of direction and precision using a 25 mm/rev lead screw for high speed at low rpm. The z actuators use 2 mm/rev lead screws for precise positional accuracy. All accessories used on the actuator, such as sensors, motor mounts and carriage-to-carriage mounting plates are off the shelf.
PBC Linear's SurePrint servo technology includes NEMA 23 step servo motors and encoder inside a servo control loop to improve overall performance (Figure 3). This motor and control technology takes advantage of the stepper motor’s strong points, creating more than 50% more torque for fast dynamic response and torque control for high operating efficiency. The design provides a rigid, accurate position at zero speed and allows travel speeds up to 200 mm/s. A 20,000-count encoder ensures precise, repeatable positioning that exceeds process capability. This closed-loop stepper technology is available with PBC Linear’s SIMO series actuators, providing a complete mechatronics solution.
3D printing control
When it came to the control system, 3D Platform's philosophy was to keep the design as simple, cost-effective and efficient as possible. "Two of the biggest needs identified during initial development was reliability and cost," notes Ben Williams, a controls designer at 3D Platform. "This is why we selected the ATmega2560 microcontroller, Arduino Mega 2560 board with Ramps 1.4 shield software. It is a good microcontroller platform allowing us to use open-sourced Marlin firmware for 3D printers."
The machine uses the Mega 2560 for I/O control and USB communication. It has everything needed to support the microcontroller and 3D printing application by connecting it to a computer and power supply. The microcontroller is installed in an operator-interface enclosure with small LCD display and three control buttons for simple power on/off control and basic operator functions.
The 3D printers use ball-screw linear actuators with each driven by SurePrint Servo motors. "The microcontroller board sends step and direction signals to the motors," notes Williams. "The SurePrint integrated motors handle all of the electronic gearing, microstepping and closed-loop encoder positioning. The SurePrint motors' internal programs store software tunable parameters to improve settling time and accuracy."
Each actuator uses Hall effect sensors for end stops, and a simple mechanical switch is set up to let the user know when the machine has run out of filament, explains Williams. "If filament runs out, the machine will stop, save its location and move to a home position where the user can easily replace the filament," he says. "With the filament replaced, a press of a button on the microcontroller interface will start printing again right where it left off."
The integrated motors have driven the innovation on the 3D printer, says Williams. "Not only do the motors give 3DP's printer more speed and torque for faster cycle times, they also improve accuracy greatly due to the close-loop control capability," he explains. "The technology used helps to fill a niche in the 3D printing market—an inexpensive, industrial 3D printer. As the 3D industry grows, the costs are coming down, which allows us to incorporate more of the new technologies that we are seeing."
Accessing and safeguarding machinery
The 3DP machine includes basic remote access for troubleshooting. "If a customer is having a problem with the printer, we can have them allow us remote access to the computer for control of the printer," says Williams. "The remote connection allows a technician to easily view the customer's process settings to assist in setting up the print process. It also allows some control functions, and the technician can check on a printer remotely and stop it, if necessary. Additional network compatibility is planned for the future, not only for more print monitoring, but also improved troubleshooting."
A big safety hurdle came up while updating the machine for CE compliance. This required the addition of emergency stopping devices, as well as a warning when the heated bed reached a certain temperature. Downward force applied to the machine in the z axis also needed to be reduced to eliminate a serious point. This was overcome by limiting the amount of current in each of the z-axis motors.
"Based on feedback from our CE certification, limiting torque at the pinch points to 150 Newtons, or less than 34 lb, eliminates the risk of permanent injury,” says Binka. "However, the end user is responsible for safeguarding machines and should consider this need when purchasing any machinery. Our machines are used in many environments where guarding is required. In most cases, extra guarding is installed on site by the end users based on factory requirements."
New types of plastic filaments are frequently introduced in the industry, and, as these filaments are released, they require different process settings and limits based on how well they perform. "Hopefully some of these new filaments will allow us to start printing faster because the equipment is capable of it," notes Williams. "I am always looking for new technology and improvements that will allow 3DP's printer to move more accurately and to complete the moves faster, so we'll be ready when the filament's print speed catches up to our equipment."