## 1 Introduction  
Consider a patient with stroke or incomplete spinal cord injury (iSCI) who uses a powered exoskeleton as an assistive device for the training of residual lower body sensorimotor skills (with additional beneficial effects of bringing the body upright for blood pressure regulation and bowel functions; overview in [1; 2; 3]). The task of the exoskeleton here is to sense leg and hip movements and to enhance or produce the joint forces such that the patient can perform the desired movements such as hip, knee and ankle flexion and extension. With standing and on-ground walking, balancing is then typically performed using hand-arm crutches that are used in a \"quadruped\"-like standing and walking style, i.e., with the upper body leaning forward and supported. This is different from the normal bipedal standing and walking style originally learned and used. Furthermore, it constrains the usage of arms and hands, and it is very exhausting [4; 5; 6].  
Physiologically, the deficits typically affect the two main constituents of sensorimotor control, i.e., the \"proactive\" part that provides voluntary action and the \"reactive\" (often reflexive) part that controls the postural stability and body balancing in response to external and self-produced disturbances (e.g., from the effects of gravity and intersegmental reaction forces; compare [4]). Current research and developments aim therefore to extend the functionality of the exoskeleton such that it provides also _posture control_[7; 8; 9; 10] in addition to the control of voluntary movements. Stability, fall-safe control, and balance recovery are also a current topic in exoskeleton research [11; 12; 13; 14; 15; 16].  
A major aim in this research field is to provide the control torque adjustments in the ankle, knee and hip joints of the exoskeleton required for voluntary action and the standing balance (unconsidered remain here targeted foot placements as an additional constituent of maintaining walking balance). It is important that the sensorimotor control of the exoskeleton corresponds to that intended and anticipated by the patient. This concerns the sensory information on joint kinematics and kinetics and foot sole pressure as well as vestibular and visual derived estimates of the kinematics of the body COM (center of mass) and the corresponding ego-motion perception in space. With major discrepancies between expected and actual sensorimotor signals, considerable extra training would be required for the patients, and patients' compliance may suffer. This paper, therefore, suggests using a method for the sensorimotor control of the exoskeleton that is human-derived and therefore complies by and large to human habits and expectations.  
This human-derived sensorimotor controller with proactive and reactive (self-balancing) properties is described in the following in abbreviated form. It has previously already been implemented into humanoid robots for proof of principle (showing, for example, that it tolerates'real world' noise and inaccuracies and copes with external and self-produced disturbances). Descriptions of this 'disturbance estimation and compensation' (DEC) controller, can be found in [7; 15; 16; 17]. Here we present it in abbreviated form and test its functionality using a novel experimental paradigm.