Principle and application of the hottest tmc428 3-

2022-07-27
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Principle and application of tmc428 3-axis stepper motor controller

Abstract: tmc428 is the latest stepper motor motion controller developed by Trinamic company, which can reduce the workload of motor control software design and development cost. The 3-axis stepping motor drive control system based on it (including tmc236 stepping motor driver) has the advantages of small size and simple control, and can control 3 two-phase stepping motors at the same time

key words: stepping motor controller tmc428

1 main performance characteristics

tmc428 is a two-phase stepping motor control chip with small size and high cost performance. It has two independent SPI ports, which can be connected with microprocessor and stepper motor driver with SPI interface to form a complete system. Its control instructions can be given by microprocessor through SPI interface. Tmc428 provides all functions related to digital motion control, including position control, speed control, micro step control and other common control functions of stepping motor. If these functions are completed by the microprocessor, it will occupy a lot of system resources, so its use can liberate the microprocessor to use resources for interface expansion and higher-level control of stepping motor. In addition, tmc236 is also a stepping motor driver with serial interface developed by Trinamic company. Daisychain structure composed of three tmc236 connections is a network structure based on serial communication, which can enable multiple devices with serial communication interfaces to transmit data in a relay manner. Tmc428 can be connected with them through SPI interface to control three two-phase stepping motors at the same time

The main features of

tmc428 are as follows:

· according to different applications, there are three packaging options: SSOP16, sop24 and dil20

· three two-phase stepping motors can be controlled at the same time, and all motors can work independently

· according to the motor motion parameters (position, speed, acceleration) given by the microprocessor, the line generates the driving pulse waveform and sequence according to the trapezoidal or triangular speed to control the position and speed of the motor. It has four operating modes. The position control has ramp mode and soft mode, and the speed control has velocity mode and hold mode

· micro step control. Micro step subdivision with 6-bit resolution is adopted. It includes full step, half step and 64 subdivisions. Each motor can select its required micro step resolution. Full step frequency up to 20kHz

· through programmable current proportional control, the motor can adopt different working currents under different working states. The control motor can work in 8 grades, which are 12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5% and 100% of the maximum current respectively

· multiple parameters can be set, including more than 20 parameters, such as maximum acceleration, maximum speed, current of motor coil during accelerated operation and position holding, micro step subdivision resolution, parameters of waveform generator and pulse generator

· the motion parameters (position, speed, acceleration) can be changed

· with 4-wire serial SPI interface, the serial communication uses a simple protocol with 32bit data length. Easy to use

· it can be connected to the motor driver through another SPI port, and its data transmission rate is as high as 1mbit/s

· low power consumption (1.25ma, 4MHz), wide clock input range and up to 16mhz clock frequency

· 3.3 long fiber reinforced materials are compatible with any thermoplastic and mixed fiber solutions, and are powered at cmos/ttl compatible levels of V or 5V

2 pin function

Figure 1 shows the pin arrangement when tmc428 is packaged with SSOP16. The functions of each pin are as follows:

1, 2, 3 pins (REF1, 2, 3): refer to switch input 1, 2, 3. A limit switch can be externally connected to trigger the internal interrupt function of tmc428. This feature is not used in this article

4 feet (test): Test feet. When using, the grounding should be near the pin as far as possible

5 pin (CLK): clock input

6 pin (nscs_c): chip selection signal input of SPI control interface. The low level is valid

7 pin (sck_c): clock input of SPI control interface

8 pin (sdi_c): SPI when a plug-in board or device is unplugged, the instrument restores the data input of the normal control interface

9 pin (sdo_c): data output of SPI control interface, high resistance

10 pin (sdo_s): drive the data output of SPI interface

11 pin (sck_s): drive the clock output of SPI interface

12 pin (nscs_s): drive the chip selection signal output of SPI interface

13 pin (V5): +5v power supply

14 pin (V33): +3.3v power supply, 470nf capacitor shall be connected externally

15 feet (GND): ground

16 pin (sdi_s): drive SPI interface data input and connect pull-up or pull-down resistors

3 internal structure and working principle

tmc428 internal structure is shown in Figure 2. Tmc428 is composed of registers and on-chip RAM of each unit. It consists of two external serial interfaces, waveform generator and pulse generator, micro step unit, multi port RAM controller and interrupt disassembly safety valve conditioning screw controller

tmc428 generally obtains control instructions from the microprocessor, and the microprocessor reads and writes tmc428 registers and ram by sending and receiving fixed length data packets. The functions of tmc428 registers and on-chip RAM are different. The register is used to store the overall configuration parameters and motion parameters of the motor, while the on-chip RAM is used to store the configuration of the drive serial interface and the micro step table. The overall parameters of the motor refer to the configuration of tmc236 in the daisy chain of the driver. The motion parameters include the current position, target position, maximum speed, maximum acceleration, current ratio of each motor, parameters of waveform generator and pulse generator, and micro step subdivision resolution. The on-chip RAM includes a data space of 64 addresses. Each address can store 24 bit wide data. The first 32-bit address data is the configuration of the daisy chain serial communication packet of the driver, and the data of the last 32-bit address is the micro step breakdown table

the competitiveness of the market will also be further improved.

after initialization, tmc428 can automatically send data packets to each tmc236 in the daisy chain, that is, after initialization, the drive serial interface can work automatically without the participation of the microprocessor. As long as the position and speed are written into the specified register, the motor can be controlled. The multi port RAM controller of tmc428 can manage the access timing of data. In this way, the microprocessor can read and write the data of registers and on-chip RAM at any time

the waveform generator can process the motion parameters stored in the register and calculate the motor motion speed curve. The pulse generator generates stepping pulse according to the speed calculated by the waveform generator. When the step pulse is generated, the drive serial interface of tmc428 will automatically send data packets to the daisy chain of the step motor driver to drive the step motor. When the micro step control is adopted, the micro step unit starts to process the step pulse generated by the pulse generator, and generates full step, half step and micro step pulses according to the selected micro step resolution, and sends them to the driver daisy chain through the drive serial port

the driver serial interface is the communication interface between tmc428 and the driver daisy chain. The length of the serial data packet from tmc428 to the driver is configurable to adapt to the SPI ring structure composed of circuits of different types and manufacturers. The maximum data length is 64bit. After initialization, the communication between tmc428 and stepping motor driver is completed automatically. Different types of drivers with SPI interfaces can be mixed to form a daisy chain structure to connect with tmc428

4 application

4.1 compatibility

tmc428 is compatible with stepping motor drive circuits produced by most manufacturers. It can be directly connected to the stepper motor driver with SPI port, and can also be connected to the common parallel port driver through additional devices. Even the stepping motor driver with stepping and direction input can be controlled by tmc428. The driving circuit tmc236 of stepping motor is simply connected into a serial daisy chain structure, and the control system of 3-axis stepping motor composed of tmc428 can give better play to the characteristics of tmc428

4.2 state detection

real time monitoring of motor running state is very important for the safety and control of the whole system. Tmc428 provides state detection function. Each time each processor sends a data packet to the tmc428, the tmc428 will return data to the microprocessor. Most motor drive circuits with serial ports are provided with different status bits (working, not working, etc.) and error flags (short circuit, open circuit, high temperature, etc.). In this way, tmc428 can provide the current motor motion parameters, working mode and status bits at any time. The data packet returned from the motor-driven daisy chain to the tmc428 is 48bit long. Tmc428 puts it in two 24bit registers. In this way, the microprocessor can directly read the information in these registers

5 application of system composition

the author uses DSP as the microprocessor of the system, and combines tmc428 and tmc236 to form a stepping motor drive control system. Tmc236 is internally integrated with a double full bridge drive circuit composed of hvcmosfet. It uses the constant current chopper drive mode to drive the bipolar two-phase stepping motor, and has the characteristics of low power consumption and high efficiency. Figure 3 shows the principle circuit diagram of 3-axis motor driver composed of 3 tmc236 and controlled by tmc428

it can be seen from Figure 3 that the system composed of special stepping motor motion controller and drive circuit has the advantages of simple peripheral circuit, strong system anti-interference ability and high reliability, which can reduce the development cost of control circuit. In addition to the power supply, the whole system has only five ICs. Therefore, it is small in size and simple in control. It is especially suitable for the drive of 3-axis step motor. Experiments show that the step time motor controlled by the driver has high positioning accuracy, good acceleration and deceleration performance, and good start stop and reverse performance. (end)

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