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The Forefront of Monozukuri (17)
Find technologies that solve on-site problems
Linear servo motors are motors that can drive a load linearly without using a ball screw or other linear conversion mechanism. They are essential items for equipment which require high-speed driving and high-accuracy positioning, and demand has been increasing every year.
For this interview, we spoke to some of the members of Servo Systems Division Design Dept. 1, about the story behind the development of compact, large thrust, low magnetic attractive force linear servo motors: a center magnet type with core and a dual magnet type with core.
Design Department 1
Akihiko Takahashi
Design Department 1
Hiroyuki Sato
Design Department 1
Yasutaka Kiguchi
When I joined the company, I started by designing rotary motors. After that, I moved to designing linear servo motors.
When I joined the company, I started by designing stepping motors. After that, I moved to designing linear servo motors.
I have been involved with linear servo motor design since joining the company.
A linear servo motor is, put simply, a motor used for linear motion where high speed and high acceleration are required.
They are used, for example, in equipment that mounts electronic components on the circuit boards of smartphones and televisions. Since electronic components used in devices such as smartphones are small, the mounting heads must be moved with high speed and accuracy to increase productivity.
Trying to do this with a rotary motor mechanically stresses the linear conversion mechanism and the speed cannot be increased. This is where we see the advantage of using linear servo motors.
In the past, the price of linear servo motors was very high. They were limited to applications where speed was essential, no matter the cost. Recently, the performance of linear servo motors has been improving, and as their price has been decreasing, their popularity has been rising. With mounters, medium-speed machines used to use rotary motors, but now even medium to low-speed machines are using linear.
Unlike rotary motors, the magnet and coil portions of linear servo motors need to be provided to the customer separately, and then integrated into their equipment. I believe that one of the reasons for their widespread use is that manufacturers have proven techniques and know-how for integrating them with equipment, and have improved the efficiency of installation.
To start, we received a request from a customer to reduce the load put on their equipment.
With a normal linear servo motor, the magnetic attractive force is applied to the linear guide. So, we worked on reducing the motor's magnetic attractive force to reduce the load on the linear guide, and allow the customer's equipment to demonstrate its strengths.
A regular linear servo motor consists of a movable armature coil and a fixed magnetic rail, and must be constructed so as to maintain a small gap between them. Since there is a very strong magnetic attractive force between them, mechanisms such as the linear guide must be strong to maintain that gap.
▼Structural cross-section of a regular core-equipped linear servo motor and direction of magnetic attractive force
In the case of the newly developed center magnet type, magnetic attractive force works on the armature coils located on the outside of the motor in the direction of the magnet rail in the center, while another magnetic attractive force works on the magnet rail in the center in the direction of the armature coils located on the outside of the motor. The respective magnetic attractive forces are generated in opposing directions, and therefore cancel out.
This product was designed to provide advantages to customers' equipment. This time, customers were very interested in the advantages of compactness and weight reduction. By eliminating the magnetic attractive force, customers' equipment can be simplified, and made smaller and lighter.
In addition, the reduced weight makes installation in equipment easier and the size of the linear guide can be reduced, so the overall equipment cost can be lowered. SANYO DENKI was the first to produce a product like the center magnet type.
In contrast, the dual magnet type requires more strength on the fixed side because the magnetic attractive force acting on the magnet rail is in one direction only and cannot be canceled out. For this reason, with a magnet rail fixed and immobile, the dual magnet type is suitable for applications that require quick and agile movement of the armature coil.
The following is a specific example that uses a dual magnet type for the Y-axis and a center magnet type for the X-axis. The Y-axis dual magnet type has a magnetic attractive force working on the fixed base. To prevent the magnet rails on both sides from collapsing, the fixed base must be thickened, and the mass must also be increased.
However, in this example, the fixed side of the Y-axis does not move, so making it lighter does not increase the speed of equipment. In fact, if it is too light vibration will occur, so to some extent it is better to make it heavy.
The X-axis center magnet type has no magnetic attractive force working on the fixed base, so thickness is not required and the mass can be reduced. Therefore, the weight of equipment can be reduced just by incorporating the center magnet type.
▼X-Y Cartesian robot (excluding linear guide)
At first, I was thinking about a conventional structure, but as it was no different than motors from other companies, I lost interest. I thought about what I would choose if I were a customer. When I wondered what kind of a motor would provide advantages to equipment, I realized, "Oh, this is what we need to do."
The hard part was determining how to incorporate our customers' wishes in our products. As we developed the system, we had to deal with issues such as making it faster, smaller, and smoother. I think it is important to solve each and every problem without giving up. I visited our customers about 2 or 3 times a month.
Because linear servo motors are incorporated in customers' equipment, we put effort into doing trial and error in the actual equipment on site.
We faced many problems in the process of prototyping and mass production, because the structure and other aspects had changed from the previous model. The center magnet type, in particular, was a first for us; neither we nor our suppliers had experience with it, which led to a lot of difficulties.
To reduce costs, at our factory we are building automated systems for mass production to reduce costs. As this motor used a new structure, we had difficulties automating production. Since the Design Dept. can't make products by itself, we have cooperated with related departments to set up mass production facilities to make high-quality products at low cost.
The performance of the motor itself is key for rotary motors, but since linear servo motors are incorporated in equipment there are some problems that cannot be solved by the motor alone. We worked together with customers to solve such problems.
The strong point for the center magnet type is the cancellation of the magnetic attractive force, and for the dual magnet type, it's the high acceleration. I think it's currently at an industry-leading level.
Since we developed it with a focus on increasing equipment speed, I imagine it will be used in applications that can take advantage of that. For now, it is used in mounters, but I believe that in the future other machines will also need higher speeds, so it will expand to a variety of applications.
I want to make products that did not exist before, but that are so useful that people are amazed when they try them.
Since I am working in development, I would like to create new products that can be widely accepted around the world. We need to keep in mind that, for our products to be used widely, we have to identify the needs of our customers and deliver them products without defects.
I like my work because I enjoy coming up with ideas to tackle challenges, and I would like to continue devising forward looking products.
Created: Jun 17, 2018