Industrial Electronics

Motion control techniques for synchronous motion

18 May 2020
Automatic Packaging Process Control

In many automation problems, two or more axes of motion are involved which must be synchronized for the motion control. The demand for automation and synchronized machines has increased due to their applications. Motion control techniques are improving day by day with the help of advanced technology. Multi-axis synchronization refers to the synchronized motion and the techniques which are used to achieve motion control.

Multi-axis synchronization

Movement on a machine in one direction, forward or backward, is known as a single axis motion. Likewise, movement in two or more directions is a multi-axis movement. In many cases, two or more axes must move together to accomplish a certain task, perhaps for production or packaging. So two or more axes that have to move together need multi-axis synchronization. This article discusses some of the techniques used to achieve multi-axis synchronization.

The mechanical control system for synchronous motion

The mechanical synchronization technique was mainly in use before electric motion control. In this approach, a central motion source is used to achieve synchronization. Gears and drive trains are used to drive the axes. The drive trains are used to deliver the motion to the right place and gears are used to measure the relative speed. This method is only useful for simple machines which have a constant gear ratio and small drive trains. For complex systems, problems like mechanical wear and backlash occur. Also, the complex arrangement will be expensive.

To synchronize two or more axes, there must be a certain relationship between them. The mechanical cams are used to follow the path when the relationship between the two axes is not constant. Designing the cam for complex arrangements is quite difficult and expensive. Clutches and brakes are used to start and stop the axes. Due to the slip between starting and stopping, they lack the precise control of the position. All the parts used in the mechanical synchronization method are subjected to wear and tear and, as a result, some parts will need replacing over time. The mechanical components also makes the machine run rough with sudden jerks occurring during operation.

Stepper and servo motion control systems

The electronic motion control system has presented the solution to the problems associated with mechanical synchronization. These solutions can be easily understood if we review the electronic motion control system. In the electronic control system, one axis of motion consists of the controller, the motor and the motor drive. With the help of a host computer or a program, the motion commands are sent to the controller. The controller generates a motion profile with these signals and updates the motor driver. The controlled input current from the motor drive helps to reach the desired position. Several motors and drives with one controller in a multi-axis system.

The two types of motion control systems are known as stepper or servo systems. Stepper systems have less power and speed compared to servo systems but they are not as expensive. Position commands send to the drive in the form of steps (low voltage pulses) in stepper systems. The alignment of the motor shaft is adjusted with the help of two motor coils. Each voltage pulse (step) adds a rotational increment on the shaft. The stepper motors range from 200 steps per revolution to 50,000 steps per revolution.

The electronic control system for synchronous motion

Drive trains and gears are removed and individual motors drive the individual axes. The controller is used to control the relationship between the position and the speed. The controller can be reprogrammed infinite times so if the working requirements change the only thing that will need to change is the program fed to the controller. The motion can be delivered directly to the required place using motors. The electronic synchronization system is more precise and has lower maintenance costs. The components of the electronic synchronization method are not subjected to mechanical wear.

The mechanical cams can be replaced by programming the complex position relation between the axes into the controller. This will improve the overall efficiency of the resulting motion and also reduce the maintenance cost and eliminate the cost of designing the cams. Using sensors, the real-time status of different parts of the machine can be updated in the controller. It allows the system to make decisions and impose delays if necessary. It is not possible to achieve this level of design flexibility and decision-making power with mechanical components.

The machine operates quietly because the programmable acceleration and deceleration provide very gentle starting and stopping of the individual axes. The overall quality of the machine increases, thanks to precise synchronization between the axes. Precise control increases the speed of individual axes, resulting in increased machine productivity.

The benefits of a flexible control system

Programmable motion control has increased the reliability, quality and productivity of machines, however, the most important benefit is flexibility. The function of mechanically synchronized machines is limited due to the fixed gears and cams. Processing a different product on the same machine is not possible because the gears and the cams would have to be changed. The programmable motion control system is only limited by the program sent to the controller. Most of the time, the machine can be used for another product by writing a new program to the controller. There is no need to change the components of the machine when the production requirements change. Therefore, programmable motion control systems have the flexibility to work for different products and can be very effective for high production.

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