# Artificial-Hand Technology--Current State of Knowledge in Designing and Forecasting Changes
## 3 Construction
### Joint Configurations  
The number of joints in a robotic hand varies depending on the chosen architecture. Commonly, fingers from index to little have 3 to 4 DOM each and are able to flex or extend, and abduct or adduct [24; 45; 109; 110; 111; 112; 113; 114]. There is some research that introduced untypical link applications or reductions [115; 106; 116]. In [90], MCP joints of palm fingers, instead of a conventional yaw-pitch type, were designed as a roll-pitch. This modification helped with in-hand manipulation that was confirmed by appropriate tests, especially 16 Cutkosky grasps that showed that abduction could successfully be replaced. The Kitech hand is known under a new name, Allegro hand, and is commercially available as one of the better prostheses. Another metacarpophalangeal solution was presented in [39; 117], where the first joints of Fingers 2-5 were constructed as one part having 1 DOM (flexion-extension). It had no trouble performing most SHAP points. Another example is the Robonaut hand [20; 118] that also included the opposition of the little and ring fingers. For the same purpose, having better adhesion, [40] utilized three CMC joints (palm fingers) that each had a single degree of motion. The feature primarily affecting whole-hand dexterity is the thumb. Its extraordinary mobility participates in the majority of grasps [62; 63]. Three methods for the first finger are utilized:  
* with opposing joint (most devices) [95; 101; 119; 120; 121; 122; 123; 124],
* placed in opposition [21; 125; 126; 89; 127; 127], and
* manually reconfigurable [70; 106; 107]. The first solution has at least 2 or 3 DOM in the CMC joint and 1 DOM in MCP and IP each. These constructions are highly biomimetic since versatility of such a thumb allows them to perform most types of human movement. More advanced structures involve [128], where the first finger has 5 DOM and highly mimics human mobility. On the contrary, the latter is unable to accomplish precise and power circular grasps due to the parallel work of the first finger to the others. The last group is represented by typical prosthetic applications where the amputee decides how a task would be executed and manually sets a thumb location [112]. In [107], there were nine lockable positions in order to meet the demands of [PERSON], but commercial prostheses show that a small posture is sufficient [129; 130]. In summary, we can conclude from all the analyzed devices that the optimal robotic hand should have 16 DOM: 1 in the DIP, PIP, and MCP joints of the index-little fingers, 1 in the MCP and IP of the thumb, and 2 DOM in the CMC joint. This configuration allows to perform most practical grasps except those where Fingers 2-5 abduction-adduction is required. The carpometacarpal can usually oppose and rotate or flex-extend, while the next two joints simply flex and extend to enclose the grasp with the palm fingers. Appliances with fewer than 16 degrees of motion lose dexterity. The most sophisticated group consist of devices with more than 19 DOM. Abduction and adduction are available as well as some additional DOM in the thumb or palm. The most humanlike robotic hand is the Shadow hand developed by the Shadow Robot company, with 23 DOM that almost ideally mimics natural construction [131]. In Figure 4, hands with five or four fingers were divided into the three groups described above and presented by time period. The most prosperous is the middle one, with 16-19 DOM, because of relatively good human abilities and not many complications, allowing to apply it in prostheses or to test algorithms and new actuators. The development of advanced ones is limited due to recent challenges in combining new technologies, i.e., actuating devices, proven in the next section and supported by appropriate tests. Consequently, legit solutions from the first two groups are more readily used. This chapter mainly includes features directly affecting device dexterity.