A bi-stable rotary solenoid is an actuator that uses electromagnetic force to perform oscillatory rotation (swing motion), often referred to simply as a rotary solenoid. Unlike motors, which utilize electromagnetic force for continuous rotation, bi-stable rotary solenoids operate within a limited angle range.

Rotary solenoids excel at oscillating between two points. Because they offer high speed and high torque, they are commonly used as a power source for mechanisms such as sorting devices, shutters, or angle-switching drives.

There are two main types of rotary solenoids: one that converts linear motion to rotational motion internally (often referred to as a “linear-to-rotary” solenoid), and another in which the rotor itself rotates directly (the bi-stable rotary solenoid). TAKANO’s solenoids use the latter design, featuring a construction similar to motors.

The rotor consists of a permanent magnet and a shaft, with the shaft supported by bearings (ball bearings, etc.) for rotation. The stator contains the coil. By reversing the current to the coil, you can switch the direction of rotation, causing the solenoid to oscillate back and forth.

The basic construction differs significantly, and their characteristics also vary. Each type has advantages and disadvantages, so please choose according to your application needs.

TAKANO’s rotary solenoids have a rotor and stator similar to a motor, but the overall structure is simpler.
The rotor is composed of a two-pole permanent magnet, while the stator contains only two-phase coils. This design does not allow full rotation; instead, it provides high-speed oscillation within a limited angle range and offers non-energized self-holding torque.

When no current is applied, the permanent magnet rotor naturally settles at the position shown in Figure A, where forces are balanced. If an external stopper is placed as shown in Figure B, the rotor tends to return to the position in Figure A, generating the self-holding torque indicated by the red arrow. The same self-holding torque is produced on the opposite stopper. The amount of holding torque depends on the stopper angle. Refer to each product’s torque characteristic graph for details.

You can also use the permanent magnet's holding force to return the rotor magnetically. This approach limits the usable angle further, but it lets you drive with even lower power consumption by eliminating the need for energizing in the return motion.
As shown in Figure C, you can place the stopper at -45° and -15° when you want the rotor to pivot 70°, with -45° as one end and -15° as the other. At -45°, a -50 N·m holding torque acts in the CCW direction. When you energize in the CW direction (blue line in Figure D), the rotor rotates until it stops at -15° (Figure E). Once you cut power, the torque at 0 W is -20 N·m, so it returns CCW magnetically.
This design is suitable for fail-safe operation. It also eliminates return springs, offering higher durability without the complexity of spring design and assembly.

When current is applied, the two-phase coils of the stator become magnetized as N and S poles. The permanent magnet in the rotor experiences attraction and repulsion in that magnetic field, causing it to rotate. Reversing the current flow reverses the rotation direction.
Unless overloaded, the rotor will not stop mid-rotation. Energized torque varies depending on the external stopper angle and the applied voltage. Refer to each product’s torque characteristic graphs for more information.

Bi-stable rotary solenoids offer outstanding performance for limited-angle oscillation or positioning. The following comparison table provides a quick overview.

To drive a rotary solenoid, you need three separate elements: a DC power supply, an electrical drive circuit, and external stoppers.

• Drive Circuit
  By switching the polarity of the supply voltage using a switch, the solenoid can oscillate back and forth. After movement is complete, you can turn off the power to leverage the solenoid’s self-holding capability, reducing both power consumption and heat generation.

Figure 2 shows a typical drive circuit diagram. We also offer dedicated drive circuit boards for our solenoids.

• Installing External Stoppers
  Most rotary solenoid models (except for a few) do not include an internal stopper. Please install a stopper to mechanically define the rotation angle.

1. Upon opening the package (with no stopper installed), the permanent magnet and the D-cut shaft will be in a stable position (either Figure F or Figure G), where magnetic forces are balanced.

2. Attach the load you want to rotate, using the D-cut on the shaft.

3. Move the load near the 0° position, then install the external stoppers at your desired oscillation angles.
   The 0° position varies by model. Please refer to the catalog’s dimensional drawing for the 0° reference. Once the stopper is in place and you release the shaft, the rotor will snap to one of the stopper positions due to magnetic force.
   Note: Use cushioning (e.g., rubber) for the stopper. Metal-to-metal contact can cause strong impacts and lead to damage.

4. Installation is complete. If the solenoid does not move when energized, possible causes include:
   
   ① The polarity of the power supply is reversed.
   　→ Solution: Reverse the polarity and check operation.
   
   ② The load is too large.
   　→ Solution: Reduce load, increase supply voltage, or reduce the rotation angle.
   
   ③ The stopper positions are incorrect.
   　→ Solution: Confirm that the external stoppers align with the 0° reference for your model.
   
   ④ The D-cut orientation does not match the 0° position.
   　→ Solution: Verify that the D-cut orientation aligns with the 0° position.

Step 1: Decide Your Stopper Method & Rotation Angle

Choose the rotation angle based on your application needs.
In addition to the standard dual-self-holding configuration, you can select a more limited angle setup to reduce power consumption by using magnetic or spring return. This allows you to reduce or eliminate energization during return motion.

Step 4: Select the Model from the Torque Characteristics Based on Steps 1, 2, & 3