# Current Status and Consideration of Support/Care Robots for Stand-Up Motion
## 3 Results
### Assist Form and Control
#### 3.2.2 Power Unit  
In assisting with STS, some or all of the required lower limb joint torque should be provided to the user by the robot. Power devices that convert power sources such as electricity into mechanical energy such as joint torque in robots are diverse, with different mechanisms and solutions used by the robots, and the power sources are also different. Reviews on power equipment are summarized in Figures 4 and 5. In the literature surveyed in this paper, as the device for generating joint torque in a robot, those using only ACTs comprised 29 cases out of 45, those using only DEVs comprised 4 cases, those using both together comprised 9 cases, and a mechanism using the user's own power comprised 1 case. Thirteen of the 29 cases using only ACTs were wearable. Of these, 12 were electric motors and 1 was an electric linear ACT. On the other hand, 16 out of 29 cases using only ACTs were of the non-wearable type. Of these, seven were electric motors, seven were electric linear ACTs, one was a hydraulic linear ACT using hydraulic power as a power source, and one was a bellows-type pneumatic ACT. Motor and linear ACTs that convert electricity to mechanical energy from the above were often adopted, and the ratio of linear ACTs was higher in the non-wearable type. In addition, one was of the wearable type and three were of the non-wearable type using only DEVs, and three cases out of four were gas springs. In addition, 9 of the 10 cases of the combined use of ACTs and DEVs were of the wearable type, 8 cases used a combination of motor and spring, and 1 case used a combination of some kind of ACT and a spring. There was one case of the non-wearable type using ACTs and DEVs, together with one that used a linear ACT and a gas spring.  
Figure 4: Summary of power unit classification in wearable robots.  
When only ACTs are used in the wearable type, [PERSON] et al's \"WPAL\" is the most common report on the use of motors [15]. WPAL is a robot targeting bilateral lower limb paralytic patients with spinal cord injury. The hip joint of the robot is designed in the inside position as in the conventional Primewalk, and it is a lower limb external skeleton robot with combined use with a wheelchair in mind. WPAL is equipped with electric motors with identical specifications in the three joints of hip, knee, and foot, and these generate standing/sitting motion and walking motion patterns controlled in real time by CPUs with a handy switching operation using a combined use walker.  
Examples of combinations of ACTs and DEVs that have been reported to be secondary to the use of ACTs alone include \"FUM-Knee Exo\" by [PERSON] et al. [14]. This robot is equipped with a linear-series elastic actuator (LSEA); the rotational motion of the motor becomes the linear motion of the ball screw, and it is transmitted as an output through a spring set. This LSEA enables the precise and robust control of human-robot interaction. Linear ACTs, which are most widely chosen along with motors in non-mounted ACTs, are devices that convert the rotational motion of motors into linear motion and are used in the \"MOBOT\" of [PERSON] et al. [39]. MOBOT causes linear ACTs to exert a force on the links in a linear-dynamic direction, creating torque in the robot arm joint, and the end-effector provides a portion of the lower limb joint torque required for to help the user with STS. In DEVs alone, gas-pulling has been the most chosen method, including STSs and the mobile-assisted robots using mobility beagles reported by [PERSON] et al. The robot has an external skeleton to be worn on the lower limb on a mobile platform, and a total of four gas springs provide users with lower thigh anteversion assist torque and knee extension assist torque in STS.