A low-cost servo control method based on SIP technology

Abstract

The present invention belongs to the technical field of servo control systems, and in particular to a low-cost servo control method based on SIP technology. The method comprises: using a 32-bit Cortex M4 chip as a control chip of an MCU controller, using another 32-bit Cortex M3 chip as a decoding chip of the MCU controller, and encapsulating the bare cores of the two chips in the same plastic package using SIP technology; the decoding chip and the control chip are connected in parallel via a 16-bit GPIO. The present invention adopts SIP technology to encapsulate the bare DIEs of the decoding chip and the control chip into the same plastic package to reduce the area of ​​the chip package and thus reduce the area of ​​the PCBA, thereby greatly reducing the overall cost of the servo controller.

Description

Technical Field

[0001] The invention belongs to the technical field of servo control systems, and in particular relates to a low-cost servo control method based on SIP technology. Background Art

[0002] In order to achieve precise position control of the servo control system, a rotary encoder is usually used to provide a higher position resolution. Take an incremental photoelectric encoder commonly used in the market as an example. The encoder outputs three sets of square wave pulses A, B and Z through the principle of photoelectric conversion. A and B are orthogonal signals with a phase difference of 90°, which are used to determine the rotation direction; Z phase is a full circle signal, and a pulse signal is generated every circle for reference point positioning; the waveforms of A, B and Z phases are as follows: Figure 1 shown.

[0003] In addition to directly outputting A, B and Z orthogonal signals, many encoders have built-in signal processing chips that compile the orthogonal signals into position signals and send them out through serial communication protocols such as 485, SPI, SSI, BISS, etc.

[0004] The common processing methods for the encoder output signal at the servo control end are as follows: Figure 2 As shown, a decoding chip is added between the servo motor encoder and the servo controller. For orthogonal signals or simple serial communication signals such as 485, the decoding chip can be an MCU with relatively ordinary performance. The MCU has an orthogonal decoding interface and can capture orthogonal pulses through a timer. At the same time, the MCU also has conventional peripherals such as SPI, I2C, and UART, and can receive conventional serial communication data. For SSI / BISS serial data with complex communication protocols, due to the requirements for the main frequency of the decoding chip and the communication rate of the interface, there are generally two existing practices. One is to use FPGA as a decoding chip and perform protocol decoding by embedding software algorithms in the FPGA; or to use a dedicated ASIC chip for decoding. The decoding chip obtains the data sent by the encoder through the orthogonal interface or the serial communication interface, obtains the position information of the motor through a specific decoding algorithm, and then sends it to the control chip (usually MCU or DSP) of the servo controller in a serial communication manner through a specific protocol (such as 485 and other commonly used protocols). Due to the existence of a dedicated decoding chip, the control chip does not need to spend a lot of computing time to process the decoding algorithm, which reduces the performance requirements for the control chip. Among them, the control chip and decoding chip used in the servo controller are both plastic encapsulated.

[0005] This common servo control system has the following defects and shortcomings:

[0006] First, as the application scope of industrial robots and service robots becomes wider and wider, the demand for miniaturization of motor control becomes more and more obvious, which requires not only the miniaturization of motors but also the miniaturization of controllers. Figure 2 In the control system shown, since both the control chip and the decoding chip are plastic-encapsulated chips, especially when a multi-pin FPGA is used as the decoding chip, it is difficult to reduce the PCBA area of ​​the control system, and the demand for miniaturization of the control system cannot be met.

[0007] Secondly, whether using FPGA or dedicated ASIC chip as the decoding chip, the price is much more expensive than ordinary MCU, and the cost of the entire control system cannot meet the customer's requirements for low cost.

[0008] Finally, it should be noted that the communication between the decoding chip and the control chip adopts serial communication. Calculated based on the maximum transmission rate of 10Mbps of the 485 bus, if 16-bit position information is transmitted, plus the frame header and frame tail, the entire transmission process will take at least 2 microseconds. When the motor rotates at high speed, the position information obtained by the control chip will have a large deviation from the actual position of the motor, resulting in unsatisfactory control effect.

[0009] In summary, the existing Figure 2 The servo control system shown is difficult to meet the requirements of miniaturization and low cost, and there is also a defect of long transmission delay between the decoding chip and the control chip. A technical solution is needed to make up for the above shortcomings. Summary of the invention

[0010] The purpose of the present invention is to provide a low-cost servo control method based on SIP technology. The present invention adopts SIP technology to encapsulate the bare DIE of the decoding chip and the control chip into the same plastic package to reduce the area of ​​the chip package and thus reduce the area of ​​the PCBA, thereby greatly reducing the overall cost of the servo controller.

[0011] To solve the above technical problems, the present invention provides a low-cost servo control method based on SIP technology, comprising the following steps:

[0012] A 32-bit Cortex M4 chip is used as the control chip of the MCU controller, and another 32-bit Cortex M3 chip is used as the decoding chip of the MCU controller. The bare cores of the two chips are packaged in the same plastic package using SIP technology.

[0013] The decoding chip and the control chip are connected in parallel via a 16-bit GPIO;

[0014] The decoding chip sends the parsed motor position information to the GPIO output through the internal bus. The establishment time of the GPIO level is 20ns. When the data is established, the decoding chip sends an interrupt signal to the control chip. After the control chip responds to the interrupt, it reads the sent position information from the GPIO of the control chip, and then sends it to the CPU of the MCU controller through the internal bus for processing.

[0015] Preferably, the two bare cores are packaged in the same plastic package by using a frame bonding method.

[0016] Preferably, the MCU SPI clock rate used by the decoding chip is as high as 72MHz, and the data of the SSI or BISS protocol is parsed by software decoding; in addition, the decoding chip also has conventional serial port peripherals and orthogonal interfaces, and can normally receive 485, 422 or SPI serial port signals and orthogonal signals.

[0017] Preferably, the GPIO of the decoding chip has a flip rate of up to 20 MHz, and the time for transmitting 16 bits of position information is 50 to 100 ns.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention uses the SIP technology to share the plastic package of the control chip with the decoding chip, which greatly reduces the PCBA area occupied by the chip package, making the layout of the controller more concise and more in line with the needs of miniaturization. At the same time, since the two chips are packaged in the same plastic package, the length of the connection line between the two is also greatly shortened, which greatly improves the anti-interference ability of the communication between the two.

[0020] 2. The decoding chip of the present invention adopts software decoding for complex communication protocols, and is also compatible with conventional serial communication signals and orthogonal signals. This allows users to design servo controllers without changing the hardware design. By replacing the connection port and the soft core, different encoder outputs can be matched, making it convenient for customers to standardize materials.

[0021] 3. The present invention uses a low-cost 32-bit MCU as a dedicated decoding chip, replacing expensive FPGA and ASIC chips, which greatly reduces the BOM cost of the entire control system. Thanks to the improvement of MCU performance, the overall performance of the controller can remain consistent with before.

[0022] 4. The present invention changes the connection mode between the decoding chip and the control chip from serial communication to parallel communication. According to calculations, the present invention can reduce the transmission delay between the decoding chip and the control chip by 90% when transmitting 16 bits of position information. At the same time, the parallel connection mode saves the cost of the level conversion chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a waveform diagram of A, B and Z phases in the prior art.

[0024] Figure 2 It is a common servo control system block diagram in the prior art.

[0025] Figure 3 It is a serial connection diagram of a control chip and a decoding chip in the prior art.

[0026] Figure 4 It is a block diagram of a low-cost servo control system based on SIP technology of the present invention.

[0027] Figure 5 It is a parallel connection diagram of the control chip and the decoding chip of the present invention in the SIP package. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in very simplified form and in non-precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0029] In the common servo controller system on the market, the control chip and the decoding chip are independently present in the PCBA in the form of plastic packaging. Figure 2 As shown. The decoding chip is responsible for parsing the signal sent by the encoder into an easily identifiable motor position signal and transmitting it to the control chip. If the encoder sends an orthogonal signal or a common serial communication signal such as 485, an ordinary performance MCU can be used as a decoding chip; if the signal sent by the encoder is a complex coded serial signal (such as SSI / BISS encoding format), the encoding chip will use FPGA or a dedicated decoding ASIC chip. The control chip and the decoding chip are connected through a serial communication interface. Taking the 485 interface as an example, the specific details are as follows: Figure 3 This common system framework is difficult to reduce the area of ​​PCBA, and the use of FPGA / ASIC increases the BOM cost, making it difficult to meet customers' requirements for miniaturization and low cost of servo control systems.

[0030] The embodiment of the present invention adopts a variety of technical means to perform optimization:

[0031] Generally speaking, the area of ​​the package is much larger than the area of ​​the bare DIE of the chip. For example, a commonly used LQFP-64Cortex M3 plastic package MCU on the market has a standard area of ​​10mm×10mm (100 square millimeters), while the area of ​​the bare DIE is 2.5mm×2.8mm (7 square millimeters). The bare DIE occupies only 7% of the area of ​​the package, which makes it possible to place multiple bare DIEs in the same package. The present invention uses the SIP technology to package the bare DIEs of the decoding chip and the control chip into the same plastic package to reduce the area of ​​the chip package and thus reduce the area of ​​the PCBA.

[0032] With the continuous progress of chip technology and technology, the main frequency of MCU is getting higher and higher, and the performance is getting closer and closer to FPGA without much fluctuation in price. For example, the main frequency of the 32-bit Cortex M0 chip with the highest main frequency on the market is 200MHz, the main frequency of the M3 chip is nearly 300MHz, and the main frequency of the M4 chip is as high as 500-600MHz, which makes it possible to decode complex SSI / BISS through MCU software. Generally, BISS uses a clock rate of up to 10MHz. The clock rate of the MCU SPI used by the decoding chip of the present invention can be as high as 72MHz, and the data of the BISS protocol can be parsed out by software decoding. In addition, the decoding chip also has conventional serial port peripherals and orthogonal interfaces, and can normally receive conventional serial port signals and orthogonal signals. Therefore, the present invention uses a 32-bit Cortex M4 chip as the control chip of the controller, and uses another 32-bit Cortex M3 chip as a special decoding chip, and the bare DIEs of these two chips are encapsulated in the same plastic package using SIP technology. Since the cost of the 32-bit Cortex M3 chip is much lower than that of FPGA or decoding-specific ASIC, the overall cost of the servo controller has been greatly reduced.

[0033] For the connection between the control chip and the decoding chip, the present invention also adopts the "serial to parallel" method for optimization. The decoding chip and the control chip can be connected in parallel through a 16-bit GPIO. For the decoding chip, the GPIO flip rate can be as high as about 20MHz. In theory, it only takes 50 to 100 nanoseconds to transmit 16-bit position information (the actual transmission process also needs to consider interruptions and the processing of some control signals), which greatly improves the communication efficiency between the decoding chip and the control chip, so that the motor position information obtained by the control chip is more accurate and can provide a better control effect. At the same time, the control chip and the decoding chip are connected by a parallel port, eliminating the level conversion chip required for 485 communication, further reducing the cost of the system.

[0034] The optimized servo control system is as follows Figure 4As shown, in order to meet the customer's requirements for miniaturization and low cost of the servo control system, the present invention provides a method of sealing the control chip and the decoding chip through the SIP technology, and replaces the expensive FPGA or ASIC circuit with the MCU through software decoding. The connection method between the decoding chip and the control chip is also optimized, and a parallel connection method is used to improve the communication transmission rate and save two level conversion chips.

[0035] There are many methods for SIP sealing. Since the bare DIE area is much smaller than the package area, the present invention uses a frame bonding method to put two bare DIEs into the same package body, and uses the plastic package of the control chip, which greatly reduces the PCBA area occupied by the chip. In terms of internal connection, the level conversion chip is omitted because of the parallel connection method. Figure 5 As shown, the decoding chip sends the parsed motor position information to the GPIO output (up to 16 bits of data) through the internal bus. In the present invention, the GPIO level establishment time is about 20 nanoseconds. When the data is established, the decoding chip sends an interrupt signal to the control chip. After the control chip responds to the interrupt, it reads the sent position information from the GPIO of the control chip, and then sends it to the CPU of the MCU through the internal bus for processing.

[0036] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A low-cost servo control method based on SIP technology, characterized in that: The steps include: A 32-bit Cortex M4 chip is used as the control chip of the MCU controller, and another 32-bit Cortex M3 chip is used as the decoding chip of the MCU controller. The bare cores of the two chips are packaged in the same plastic package using SIP technology. The decoding chip and the control chip are connected in parallel via a 16-bit GPIO; The decoding chip sends the parsed motor position information to the GPIO output through the internal bus. The establishment time of the GPIO level is 20ns. When the data is established, the decoding chip sends an interrupt signal to the control chip. After the control chip responds to the interrupt, it reads the sent position information from the GPIO of the control chip, and then sends it to the CPU of the MCU controller through the internal bus for processing.

2. A low-cost servo control method based on SIP technology as claimed in claim 1, characterized in that: The two bare cores are encapsulated in the same plastic package by using the frame bonding method.

3. A low-cost servo control method based on SIP technology as claimed in claim 1, characterized in that: The MCU SPI clock rate used by the decoding chip is as high as 72MHz, and the data of the SSI or BISS protocol is parsed through software decoding; in addition, the decoding chip also has conventional serial port peripherals and orthogonal interfaces, and can normally receive 485, 422 or SPI serial port signals and orthogonal signals.

4. A low-cost servo control method based on SIP technology as claimed in claim 1, characterized in that: The GPIO of the decoding chip has a flip rate of up to 20 MHz, and the time for transmitting 16 bits of position information is 50 to 100 ns.

Images