Locomotion simulation device

Abstract

A locomotion simulation device comprising a harness arranged to limit the movement of a user in three degrees of freedom: translation along the x-axis, translation along the y-axis, and rotation around the z-axis of an imaginary system of orthogonal axes. A support element actuator assembly is configured to actuate a support element in the limited three degrees of freedom. A force / torque sensor is configured to determine the force and / or torque exerted by a foot of the user on the support element in the limited three degrees of freedom of movement. A controller is configured to determine a velocity profile for the support element within the limited three degrees of freedom based on the determined force and / or torque and to control the support element actuator assembly to actuate the support element in accordance with the determined velocity profile such that the support element moves within the limited three degrees of freedom. (Fig. 2)

Description

P36729NL00 / SMI Title: Locomotion simulation device BACKGROUND Locomotion is the movement of a person within the world. Walking or running are examples of locomotion. A person uses their limbs to exert a force on the surface on which they are standing. The reactionary force results in a propulsion of the person, which allows them to move within the world. Locomotion is simulated for several use cases. For example, a traditional treadmill simulates walking or running in the real world while the user of the treadmill remains within a limited area, i.e., the user remains confined to the bounds of the treadmill while he or she experiences the sensation of walking or running. Similarly, in Virtual Reality (VR) applications, users interact with a virtual world. In such applications, typically the user is represented by a digital avatar within the virtual world. The user interacts with the virtual world through this avatar. VR applications attempt to immerse the user within the virtual world: the user feels one with the avatar, and thereby gets the impression of being within the virtual world as if itwere the real world. VR headsets provide for one aspect of that immersion by projecting the virtual world close to the eyes of the user and allowing the user to look around in the virtual world by tracking head and / or eye movements. ManyVR systems, however, lack the simulation ofhuman locomotion. In manyVR systems, the user is stationary while navigating the virtual world, e.g., using a controller. lmmersion is negatively affected since the movement of the virtual avatar in the virtual world does not influence the user in the real world. And vice versa, the movement of the user in the real world does not influence the movement of the virtual avatar in the virtual world. Thus, the user is confronted with the physical boundaries in which the user is located. Further, by allowing movement within the virtual world but no or limited movement in the real world, the user may experience motion sickness. Several solutions to this locomotion problem have been proposed. Classical treadmills, which are optionally redesigned to allow movement of the user in multiple directions, have long been used in fitness applications. They consist of a belt-pulley system driven by an actuator. Historically, treadmills have not been well-suited to applications that require a change in speed since they rely on a flywheel to keep the velocity of the belt constant regardless of the user inputs. This flywheel introduces a large inertia into the system that reduces the dynamic response. Additionally, the vertical forces are transferred from the belt to the ground directly, causing significant friction losses. Slidemills are a type of treadmill which reduce the friction between the floor and the shoe of the user to a very low value. When the user moves his foot away from the centre (as if making _ 2 _ a step), the foot will slide back to the centre because of the low-friction and gravity. This sliding motion is achieved either by tilting the entire floor surface, or by making the floor bowl-shaped with slopes towards the edges. This allows a type of movement that is like walking. However, because slidemills are non-actuated devices, slidemills do not consider any of the dynamics used in actual walking motion. Because of this, users generally describe the experience of walking on slidemills as difficult to learn and unpleasant over longer periods. Large-scale free roam VR solutions offer more mobility to the user, allowing for a wider range of movement and exploration within the virtual environment. These solutions, however, require a significantly larger physical space and are limited by the layout of the room. Additionally, the large-scale free roam VR solutions pose a greater safety risk due to the potential for collisions with other users or obstacles within the space. An object of the invention is to overcome some or all of the identified disadvantages of existing locomotion simulation devices or at least to provide an alternative to existing locomotion simulation devices. SUMMARY The present invention relates to a locomotion simulation device. An imaginary system of orthogonal axes comprising an x-axis, a y-axis, and a z-axis is defined, each axis defining two degrees of freedom, the two degrees offreedom being translation along and rotation around the axis. In the imaginary system of orthogonal axes, an xy-plane defined by the x-axis and the y- axis corresponds to the horizontal, axial, or transverse plane with respect to the user of the device. The z-axis is the vertical axis, and so a zy-plane defined by the z-axis and the y-axis corresponds to the coronal or frontal plane with respect to the user of the device; a zx-plane defined by the z-axis and the x-axis corresponds to the sagittal or longitudinal plane with respect to the user. The locomotion simulation device comprises a movement-limiting device which comprises a harness arranged to limit the movement of a user of the device in three degrees of freedom of movement, the limited three degrees offreedom of movement being translation along the x-axis of the imaginary system of orthogonal axes, translation along the y-axis of the imaginary system of orthogonal axes, and rotation around the z-axis of the imaginary system of orthogonal axes. The locomotion simulation device further comprises a stationary element supporting the harness. In this document, the term limited three degrees offreedom refers to those three degrees offreedom that, in use of the device, are limited by the harness. The locomotion simulation device further comprises a support element arranged to support a foot of the user; a support element actuator assembly configured to actuate the support element in the limited three degrees of freedom; and a force / torque sensor configured to _ 3 _ determine the force and / or torque exerted by the foot of the user on the support element in the limited three degrees offreedom of movement and to generate a force / torque sensor signal representative of said force and / or torque. In this document, the term degree offreedom is used as a synonym for degree of freedom of movement. The locomotion simulation device further comprises a controller. The controller is configured to receive, from the force / torque sensor, the force / torque sensor signal representative of the force and / or torque with which the users foot interacts with the support element in the limited three degrees offreedom of movement; to determine a velocity profile for the support element within the limited three degrees offreedom based on said force / torque sensor signal; and to control the support element actuator assembly to actuate the support element in accordance with the determined velocity profile such that the support element moves within the limited three degrees of freedom. The device according to the present invention performs locomotion simulation by 1) limiting the movement of the user; and 2) simulating the sensation of movement. The limiting is achieved by the harness of the device that limits, or optionally blocks, movement of the user in three limited degrees offreedom of movement. Therewith, within those three limited degrees of freedom of movement, the user is held at a fixed location or at least only has a small envelope in which they can move. The device mimics or simulates the sensation of movement that the user would experience in the real world by moving a support element within the limited degrees of freedom; therewith, the support element embodies the surface on which the user is walking or running, underneath the user. Optionally, the support element moves in the same direction as the direction of the force exerted by the user on the support element as measured by the force / torque sensor. The support element moves proportionally with the magnitude of the force exerted by the user on the support element as measured by the force / torque sensor. Optionally, the velocity profile for the support element comprises an x-velocity (i.e., the linear velocity for the support element along the x-axis), a y-velocity (i.e., the linear velocity for the support element along the y-axis) and an angular velocity (i.e., the angular or rotational velocity for the support element around the z-axis). For example, these velocities are determined based on the forces exerted by the user on the support element in a respective limited degree of freedom: the x-velocity is determined based on the force exerted by the user along the x-axis, the y-velocity is determined based on the force exerted by the user along the y-axis, and the angular velocity is determined based on the torque exerted by the user about the z-axis. Optionally, the x- and y-velocities are additionally determined based on the torque exerted by the user about the z-axis. In the real world, when a person exerts a force on the ground, the person experiences an acceleration which results in the movement of the user relative to the ground. Since the harness of the device limits the movement of the user, such acceleration of the user in the limited three _ 4 _ degrees offreedom is not possible, or possible only to a limited extent. Therefore, the support element, which embodies the surface on which the user is walking or running, is moved with respect to the user instead of the user moving with respect to the support element. Therewith, the support element embodies the surface on which the user is moving. The movement of the support element results in the user experiencing movement as if he or she would be moving with respect to that surface. The support element is configured to be at any position within the xy-planewhere the foot of the user may land. For example, the support element, which is for example a footplate, is configured to be moved to the position within the xy-plane where the foot of the user may land. Optionally, the support element is further configured to be at any rotational position about the z- axis, such that the orientation of the support element conforms to the orientation of the foot of the user. In other examples, the support element is in a stationary location. ln such examples, the support element spans an area within the xy-plane that is sufficiently large such that the foot of the user is supported wherever it lands within the xy-plane. ln such examples, the support element is for example a treadmill, or the support element comprises several smaller elements such as rollers. Therewith, any movement within the xy-plane of the user is supported. This includes fonNards steps (i.e., steps along the x-axis), sidesteps (i.e., steps along the y-axis), and any other steps at an angle within the xy-plane. Existing solutions, e.g. traditional treadmills, in general limit the movement of the user in a single direction, e.g., the fonNards direction. To determine the velocity profile for the support element, the force / torque sensor of the device measures the force with which the foot of the user interacts with, Le, pushes against, the support element. Additionally, the force / torque sensor measures the torque with which the foot of the user interacts with, Le, provides a rotational moment (around the z-axis, i.e., around the vertical) to the support element. The support element is for example a footpad which has dimensions that accommodates the foot of the user but may also comprise individually moveable support elements such as rollers or tiltable plates. The force and / or torque exerted by the foot of the user on the support element in some examples is / are measured directly within the support element by the force / torque sensor. ln alternative examples, said force and / or torque is / are measured indirectly in other locations of the device, such as the harness: the force and / or torque exerted by the user on the harness in the three degrees offreedom is opposite to, but identical in magnitude to the force and / or exerted by the user on the support element (within a margin of error, defined by the amount of movement of the user that is still allowed by the harness). The velocity profile for the support element thus denotes the speed and the direction in which the support element is to be moved to simulate locomotion simulation. The velocity profile for the support element has a certain relationship to the velocity profile of the user if the movement of the userwould not be limited by the harness, i.e., the velocity profile of the user _ 5 _ when moving in the real world. Said relationship is for example that the velocity profile for the support element is identical in magnitude but opposite in direction to the velocity profile of the user ifthe movement of the userwould not be limited by the harness. ln examples wherein the support element is a footpad, the velocity profile for the support element corresponds to a translation of the support element within the xy-plane and / or a rotation of the support element around the z-axis. Alternatively, in examples wherein the support element is a roller or a tiltable plate, the velocity profile for the support element corresponds for example to a rotation and / or a tilting motion of the support element. The harness, the support element, the support element actuator assembly, and the controllerwork in unison to perform natural locomotion simulation. The support element is actuated within the xy-plane, thereby simulating a 2-dimensional surface, as would be expected by the userwhen walking on a surface in the real world. ln comparison with slidemills, for example, the present invention allows for more natural movement, since the foot of the user is supported by the support element as expected when walking on a surface in the real world. There is thus no longer a need to train users to use the device correctly, or a training time at least is minimized. Due to the measurement of the force / torque exerted by the foot of the user on the support element, the support element is moved by the support element actuator assembly in the limited three degrees of freedom, e.g., within the xy-plane, to accurately simulate the movement of the user that results from the force and / or torque that the user exerts on the support platform. As a result, the device is highly reactive to changes in the velocity profile of the user, which results in natural locomotion simulation. For example, when the force that the user exerts on the support platform in the backwards direction (i.e., along the x-axis towards the back of the person) increases, then their acceleration in the forwards direction increases, thereby resulting in an increased velocity profile of the support element along the x-axis. This is the result of the user pushing the simulated surface, i.e., the support element, harder away from themselves. In the real world, this would result in the user accelerating faster in the forward direction, i.e., moving away faster in the forward direction. The device simulates such movement by moving the support element backwards. Thus, instead of the surface (in the real world) defining a fixed reference frame along which the user moves, the user of the device defines a fixed reference frame along which the support element moves, since the movement of the user is limited / blocked by the harness in the three degrees offreedom of movement. The velocity profile for the support element determines the speed of the support element along the three degrees of freedom, i.e., translation along the x- and y-axis, and rotation around the z-axis. These three degrees offreedom allow to simulate any possible movement of the user within the xy-plane, including forwards steps (translation along the x-axis), sidesteps (translation along the y-axis), and turns (rotation around the z-axis).The support element actuator assembly _ 6 _ is thus driven to move the support element in accordance with the velocity profile for the support element such that the movement of the support element corresponds to the velocity profile. The direction of movement of the support element caused by the support element actuator corresponds to the directions of the forces and / or torques exerted by the foot of the user on the support element, as measured by the force / torque sensor. The velocity profile for the support element mirrors the velocity profile which the userwould experience in the real world on solid ground. For example, the force / torque sensor comprises a strain gauge. ln some examples, the force / torque sensor comprises multiple strain gauges, each of the strain gauges being arranged to measure the force and / or torque in one or more of the three limited degrees of freedom. In an embodiment, the harness is arranged to allow movement of the user in the degrees of freedom of movement other than the limited three degrees of freedom of movement. In this embodiment, the users movement are constrained by the harness in the translational direction for the x- and y-axis (forward and sideways movement), as well as the rotation along the z-axis (yaw). The users movement in the remaining three degrees of freedom, i.e., rotation around the x-axis (roll), rotation around the y-axis (pitch), and translation along the z-axis (jumping / kneeling), is not limited by the harness. This means that then user is able to move relatively unconstrainted within those remaining three degrees of freedom. In other words, the harness is arranged to limit movement of the user of the device in the following three degrees of freedom: translation along the x-axis of the imaginary system of orthogonal axes, translation along the y-axis of the imaginary system of orthogonal axes, and rotation around the z-axis of the imaginary system of orthogonal axes. In this embodiment, the harness is arranged to allow movement of the user of the device in the following three degrees of freedom: rotation around the x-axis, rotation around the y-axis, and translation along the z-axis. In an embodiment, the force / torque sensor is configured to determine the force exerted by the foot of the user on the support element within the xy-plane of the imaginary system of orthogonal axes. The force / torque sensor thus is configured to determine the linear force, exerted by the user on the support element in the two dimensions of the xy-plane, i.e., the xy-force exerted by the user in the forwards-backwards direction (x-axis) as well as the sideways direction (y-axis). These forces determine the direction in which the user intends to move _ 7 _ within the xy-plane, i.e., which translational movement the user intends to perform. For example, a force directed backwards and to the right means that the user is pushing the support element backwards and to the right, which means that the user intends to make a forward step to the left. The force / torque sensor is further configured to determine the torque exerted by the foot of the user on the support element about the z-axis of the imaginary system of orthogonal axes. The force / torque sensor thus determines the torque exerted by the user around the vertical direction (z-axis). Said torque determines the rotation around the z-axis that the user intends to take. For example, a torque directed in counterclockwise direction around the z- axis means that the user intends to rotate their body clockwise. This means that the feet of the user essentially move (in the real world) or are to be moved (by the device) in counterclockwise direction, when seen from the centre of mass of the user. The controller is further configured to determine the velocity profile for the support element based on the force exerted by the foot of the user on the support element within the xy-plane of the imaginary system of orthogonal axes and on the torque exerted by the foot of the user on the support element about the z-axis of the imaginary system of orthogonal axes. Since the movement of the user is limited in the limited three degrees of freedom by the harness, the intended movement of the user in these three degrees of freedom cannot be physically completed by the user. lnstead, the device is configured to simulate the intended movement of the user. Thus, the controller is configured to determine the extent of movement of the support element - which supports the foot of the user to appropriately simulate the intended movement of the user. The velocity profile for the support element thus represents, e.g., the movement of the support element within the xy-plane. As a result, the linear force and torque exerted by the user on the support element cause the support element to move such that the intended movement of the user is accurately simulated. For example, a linear force in the backwards (x-axis) direction and leftwards (y-axis) direction cause the support element to move backwards and leftwards, such that the support element moves beneath the userwhen seen from the centre of mass of the user. Said movement of the support element results in the foot of the user which is supported by said support element to also move in the direction in which the support element is moved. Thereby, the movement of the user is accurately simulated by moving the surface on which the user is standing while the user remains stationary. Optionally, in this embodiment, the device further comprises a rotational actuator configured to rotate the support element around the z-axis of the imaginary system of orthogonal axes. The controller is further configured to instruct the rotational actuator to rotate the support element based on the torque exerted by the user on the support element. For example, a linear force in the backwards (x-axis) direction and leftwards (y-axis) direction _ 8 _ combined with a torque in the clockwise direction (z-axis) cause the support element to move backwards and leftwards, as well as rotated clockwise. By rotating the support element around the z-axis, turns of the user are accurately simulated: in a rightwards turn, the feet of the user essentially move leftwhen viewed from the centre of mass of the user. In an embodiment, the harness is configured to be worn on a torso of the user and the harness is arranged to limit the movement of the torso of the user in the limited three degrees of freedom of movement. The torso, or trunk, of the user corresponds to the core of the body. The torso thus corresponds to the body without the head, neck, and limbs. In this embodiment, the movement of the whole torso or parts thereof are limited in the limited three degrees of freedom. The other parts of the body are free to move in the limited three degrees of freedom although the movement of these other parts is also limited by virtue of being attached to the torso of the user. So, the feet and legs of the user are not directly limited by the harness in the limited three degrees of freedom and in that sense, the user is able to move their feet and legs within a constrained space around the torso of the user. While the foot of the user is supported by a support element of the device, the translation of the foot of the user within the xy-plane is determined by the movement of the support element. When the foot of the user breaks contact with the support element, the foot of the user is free to move in any direction until it makes contact with the support element again. The possible movement of the foot of the user either imparted by the support elementwhen the foot is supported by the support element or imparted by the userwhen the foot is not supported by the support element defines a walking envelope around the centre of mass of the user. In an embodiment, the harness is arranged to limit the movement of the user at the waist of the user in the limited three degrees of freedom of movement. The centre of mass of the user is slightly below the belly button, i.e., around the height of the waist of the user. Thus, when limiting the movement of the user at the waist, the centre of mass of the user is fixated in the limited three degrees of freedom. The remainder of the body of the user is free to be moved in relation to this centre of mass as its movement is not limited by the harness. So, the legs and feet of the user are free to move in relation to the centre of mass of the user, as well as the head and neck and the torso of the user above the waist. However, since these parts of the body are in some way connected to the waist, the movement of these parts of the body are also (indirectly) limited by the harness. For example, while it may be possible to slightly rotate the torso above the waist, it is not possible for the user to make a full turn around the vertical axis (i.e., the z-axis). _ 9 _ In an embodiment, the harness is arranged to block the movement of the user in the limited three degrees of freedom of movement. When fully blocking movement in the three degrees of freedom, the force / torque sensor is capable of more accurately determining the force and / or torque with which the users foot interacts with the support element in the three degrees of freedom, because any forces exerted on the support element represents an intended movement of the user. In an embodiment, the support element is a footpad. In this embodiment, the device further comprises a position sensor configured to determine the position of the foot of the user within the xy-plane and optionally along the z- axis of the imaginary system of orthogonal axes and to generate a foot position sensor signal representative of said position of the foot of the user; In this embodiment, the controller is further configured to receive, from the position sensor, the foot position sensor signal; to determine, based on the force / torque sensor signal and / or the foot position sensor signal, whether the foot of the user is in contact with the support element; to, in case that it is determined that the foot of the user is not in contact with the support element, control the support element actuator assembly to move the support element within the xy-plane of the imaginary system of orthogonal axes to the position of the foot of the user; and to, in case that it is determined that the foot of the user is in contact with the support element, proceeding with the steps of determining the velocity profile for the support element and controlling the support element actuator assembly to move the support element in accordance with the determined velocity profile. In this embodiment, the footpad is dimensioned to support the foot of the user. For example, the footpad is in a rectangular shape, optionally with rounded corners, and dimensioned to be larger, such as 20% or more, than a typical foot size of a user. For example, the footpad is 25% or 50% or 75% or 100% larger than the typical foot size of the user. The footpad can be manufactured of any suitable material, for example metal or aluminium. The surface of the footpad is free of any obstructions and therefore is generally flat, thereby resembling a flat surface that is simulated by the device. When the foot of the user is in contact with the footpad, the controller is configured to control the actuator to actuate the footpad in such a way as to simulate the acceleration and / or movement of the user which pushes against the footpad, based on the force and / or torque that is / are determined to be exerted on the footpad. This is achieved by moving the footpad in accordance with the determined velocity profile, as explained above. At some point in their movement, the user lifts their foot, breaking contact with the footpad. Such lifting of the foot corresponds to a natural movement: when moving in the real world: the user would push against the floor to accelerate, and then take a step forward to _ 10 _ continue moving fonNards. In the real world, the surface on which the user moves typically extends in the xy-plane and so the user can run, theoretically, forever in any direction. In this embodiment, the device simulates such a surface and thus ensures that the user has a surface (embodied by the support element) to step onto when moving their foot back downwards. To achieve this, the position sensor detects the position of the foot of the user while the foot of the user is not in contact with the support element. To determine whether the foot of the user is in contact with the footpad, the force / torque sensor signal is for example used by the controller: if the force / torque sensor signal exceeds a predefined threshold, then the foot of the user is determined to be in contact with the footpad; if the force / torque sensor signal is below said predefined threshold, then the foot of the user is determined not to be in contact with the footpad. Alternatively or additionally, the position sensor signal is for example used by the controller to determine whether the foot of the user is in contact with the footpad: if the position sensor signal indicates that there is, along the z-axis, a gap in between the foot of the user and the footpad that is arranged to support that foot, then the foot of the user is determined not to be in contact with the footpad. For example, the position sensor comprises a camera and an object tracking module configured to identify the foot of the user and to determine the position of the foot of the user. The camera is pointed towards the foot of the user and is configured to take a series of images and / or a video of the foot of the user. Said series of images and / or video is subsequently received by the object tracking module, which is configured to detect the foot of the user in the images and / or video captured by the camera. The position sensor continuously tracks the position of the foot of the user while it is not in contact with the footpad, i.e., the position sensor determines the position of the foot of the user with a suitable frequency. The position sensor alternatively is any sensor capable of detecting the position of the foot of the user, such as: an infrared tracking system that tracks a sensor or a reflector provided at the foot of the user; a camera configured to track individual feet of the user; or a full-body tracking system. While the position sensor tracks the position of the footpad, the footpad is , based on this tracking, simultaneously moved towards the location of the foot of the user within the xy- plane when the foot of the user is not in contact with the footpad. This mode is called the tracking mode. Thereby, when the user moves their foot downwards, the footpad is in a position beneath the foot of the user, and the foot of the user makes contact again with the footpad at some point in the downwards movement of the foot of the user. Once contact of the foot with the footpad is re-established, the controller again switches to the other mode of _ 11 _ control, in which the footpad is moved in accordance with the determined velocity profile of the footpad. This mode is called the acceleration mode. In this way, movement of the user in any direction within the xy-plane is supported by the device. For example, when moving forward, the foot of the user goes through a cycle of being in contact with the footpad, pushing against the footpad, and then breaking that contact as if taking a step in the real world. The device tracks the foot of the user to ensure that the user feels a surface beneath themselves at all points in time where that is necessary (i.e., when making contact with the simulated surface such as a floor). The controller further switches between the tracking mode and the acceleration mode to accurately simulate the locomotion of the user as if they were moving on a real surface. In an embodiment, the position sensor is further configured to determine the position of a portion of the foot of the user, preferably the tip or heel of the foot of the user, within the xy-plane of the imaginary system of orthogonal axes and to generate a foot portion position sensor signal representative of said position of the portion of the foot of the user. The controller is further configured to receive, from the position sensor, the foot portion position sensor signal; and, in case that it is determined that the foot of the user is not in contact with the support element, to control the support element actuator assembly to move the support element within the xy-plane such that a portion of the support element corresponding to the portion of the foot of the user is moved to the location of the portion of the foot of the user. The controller is thus configured to control the support element actuator assembly to move the support element within the xy-plane based on the position sensor signal representative of the position of the portion of the foot of the user within the xy-plane of the imaginary system of orthogonal axes. The position sensor, which for example comprises a camera and an object tracking module, is configured to track the portion of the foot of the user. As a result, the full foot of the user is not required to be visible for the camera, only the portion that is tracked. When the tip of the foot is tracked, the front portion of the support element is moved within the xy-plane towards the detected position of the tip of the foot. Conversely, when the heel of the foot is tracked, the rear portion of the footpad is moved within the xy-plane towards the detected position of the heel of the foot. In an embodiment, the position sensor is further configured to determine a rotation of the foot of the user around the z-axis of the imaginary system of orthogonal axes and to generate a foot rotation position sensor signal representative of said rotation of the foot of the user around the z-axis of the imaginary system of orthogonal axes. _ 12 _ In this embodiment, the support element actuator assembly comprises a rotational actuator configured to rotate the support element around the z-axis of the imaginary system of orthogonal axes. For example, the rotational actuator is arranged within the support element. In this embodiment, the controller is further configured to receive, from the position sensor, the foot rotation position sensor signal; and, in case that it is determined that the foot of the user is not in contact with the support element, to control the rotational actuator to rotate the support element around the z-axis of the imaginary system of orthogonal axes such that the rotation of the support element around the z-axis of the imaginary system of orthogonal axes corresponds to the rotation of the foot of the user around the z-axis of the imaginary system of orthogonal axes. The controller is thus configured to control the rotational actuator to rotate the support element about the z-axis of the imaginary system of orthogonal axes based on the position sensor signal representative of the position sensor signal representative of said rotation of the foot of the user around the z-axis of the imaginary system of orthogonal axes. Thus, in this embodiment, the footpad is not only moved towards the position of the foot of the user, but also rotated such that the rotation of the support element corresponds to the rotation of the foot of the user. Thereby, it is ensured that if the user rotates their feet around the z-axis while the foot of the user is not in contact with the footpad, that the foot of the user is fully supported by the support element once the foot of the user makes contact with the support element again. The rotational actuator is for example a servomotor. A concrete example of a suitable servomotor is the commercially available PRHD2 servomotor manufactured by STXI Motion. In an embodiment, the support element actuator assembly comprises a first arm and a second arm. The first arm has a first end hinged to the stationary element at a first hinge. The first arm further has a second end hinged to a first end of the second arm at a second hinge. In other words, the second arm extends from the first arm at a second hinge. The support element is provided at a second end of the second arm. The second end of the second arm is opposite the first end of the second arm, i.e., opposite the second hinge. Effectively, in this embodiment, the support element actuator assembly corresponds to a serial SCARA robot arm configuration, having a jointed two-link arm layout, wherein the support element is provided, i.e., arranged, at one end of the robot arm. The other end of the robot arm is supported by the stationary element. Optionally, the end of the robot arm at which the support element is provided, i.e., the second end of the second arm, is supported on the ground by a wheel. The wheel provides for additional stability, ensures that the robot _ 13 _ arm remains rigid within the xy-plane, and further supports the userwhen their foot is placed on the support element. Optionally, in this embodiment, the support element is rotatably coupled to the second end of the second arm via the rotational actuator. Thus, rotation of the support element around the z-axis is provided by the rotational actuator. The point of rotation is provided at the second end of the second arm, i.e., at the location at which the support element is coupled to the SCARA robot arm configuration. Optionally, in this embodiment, the support element actuator assembly comprises a first actuator and a second actuator. The first actuator is configured to pivot the first arm about the first hinge. The second actuator is configured to pivot the second arm about the second hinge. The pivoting of the first arm about the first hinge and the pivoting of the second arm about the second hinge causes the footplate to move within the xy-plane of the imaginary system of orthogonal axes. The first and second actuators are for example motors that produce a rotational movement. The first and second actuators are for example rotary actuators such as for example servomotors. A concrete example of a suitable servomotor is the commercially available PRHD2 servomotor manufactured by STXI Motion. The rotational movement of the first motor is transferred to the first arm (e.g., at the first hinge) to pivot the first arm about the first hinge. The rotational movement of the second motor is transferred to the second arm (e.g., at the second hinge) to pivot the second arm about the second hinge. For example, the first and second motors are placed close to the first and second robot arms, respectively. Alternatively, the first and second motors are placed at some distance to the first and second robot arms, wherein the rotation of each motor is transferred to their respective hinge using e.g. a belt or a chain. In an embodiment, the device comprises two support elements, wherein the support elements are footpads, both footpads being arranged to each support a distinct foot of the user; and two force / torque sensors, each configured to determine the force and / or torque exerted by the foot of the user on a distinct footpad in the limited three degrees offreedom of movement and to generate a force / torque sensor signal representative of said force and / or torque. In this embodiment, the support element actuator assembly is configured to actuate the footpads in the limited three degrees offreedom and the controller is configured to receive, from each force / torque sensor, a force / torque sensor signal representative of the force and / or torque with which the users foot interacts with a respective footpad in the limited three degrees offreedom of movement; to determine a velocity profile for each footpad within the limited three degrees offreedom based on a force / torque sensor signal received from a force / torque sensor; and to control each support element actuator assembly to actuate a respective footpad in _ 14 _ accordance with the determined velocity profile such that the respective footpad moves within the limited three degrees of freedom. In this embodiment, the device, in use, is configured to support both feet of the user, thereby allowing the accurate simulation of walking or running. The velocity profile of each individual footpad is determined as explained above with respect to the other embodiments, and the respective footpad is moved in accordance with the determined velocity profile. For example, the support element actuator assembly comprises two support element actuators, each support element actuator being configured to actuate a respective footpad in the limited three degrees of freedom. Each of these support element actuators may comprise a first arm and a second arm in a SCARA-configuration, the first arm and second arm being driven by respective first and second actuators. In a variant of this embodiment, the velocity profile for each respective footpad is determined based on the force / torque sensor signal received from both force / torque sensors. In this variant, the history of the force measurements performed by both force / torque sensors is used to determine the velocity profile for both footpads. This stems from the observation that, in the real world, when a person starts running, they will exert a force with one of their feet (the left leg or the right foot) on the surface on which they are standing. As a result, their body is propelled forwards (or backwards, depending on the direction of the force thatwas applied). In other words, their body experiences an acceleration imparted on it by the force that is exerted by the foot of the person on the surface. Said acceleration results in their body having a velocity imparted on it. The user will then lift their other foot and subsequently, while their body is being propelled fonNards, place that foot at a location which is farther in the direction of the velocity. They will then exert a force on that foot once it has made contact with the surface again. If the force increases, then the acceleration increases; if the force decreases; then the acceleration decreases. In the real world, the feet of the user move with respect to the surface as a result of the velocity imparted on them, which is the result of the force exerted by the feet of the user on the surface. It is noted that the velocity of each foot is the result of the history of the force exerted by each foot on the surface. lndeed, if the left foot exerts a force on the surface, then the right foot, once it has been placed back on the surface, initially also carries the same velocity thatwas imparted by the left foot. Therefore, in this variant, the velocity profile for an individual footpad is determined based on the force / torque sensor signal received from both force / torque sensors. For example, the velocity profile of an individual footpad is determined based on a history of the force / torque sensor signal received from both force / torque sensors. When one of the feet of the user exerts a force on its respective footpad, then the sensor signal representing this force is also taken into accountwhen the velocity profile of the footpad of the other foot once _ 15 _ the user exerts a force with that foot on its respective footpad. For example, the same velocity is imparted to the footpad configured to support the other foot once a force is exerted on said footpad. In other words, the velocity of one of the footpads is used to initialize the velocity of the other footpad. After said initialization, the force / torque sensor signal of the force / torque sensor corresponding to the footpad is used to determine a new velocity profile for said footpad. For example, if the force on that footpad in the direction of the velocity increases, then the acceleration of the foot, and therefore also the velocity of the footpad supporting that foot also increases. Conversely, if the force on that footpad in the direction of the velocity decreases, then the acceleration of the foot, and therefore also the velocity of the footpad supporting that foot also decreases. In a variant of this embodiment, the position sensor is configured to determine the position of both feet of the user within the xy-plane of the imaginary system of orthogonal axes and to generate a respective foot position sensor signal representative of said position of each foot of the user. Alternatively, the position sensor generates a single foot position sensor signal representative of the position of both feet of the user. In this variant, the controller is further configured to receive, from the position sensor, the respective foot position sensor signals; to determine, based on the force / torque sensor signal and / or the respective foot position sensor signals, whether a respective foot of the user is in contact with a respective support element; to, in case that it is determined that the respective foot of the user is not in contact with the respective support element, control the support element actuator assembly to move the respective support element within the xy-plane to the position of the respective foot of the user; and to, in case that it is determined that the respective foot of the user is in contact with its respective support element, proceed with the steps of determining the velocity profile for the respective support element and to control the respective support element actuator assembly to move the respective support element in accordance with the determined velocity profile. The two support elements of the device are, in use, moved towards the position of the feet of the user such that the support elements are in a location to support both feet of the user. That is, when the user moves either foot of its respective support element, the position sensor tracks the respective foot while it is not in contact with its respective support element. The resulting position sensor signals are received by the controller, which determines a new position for the respective support element to move to. Based on the determined new position, the controller is configured to control the support element actuator assembly (e.g., one of the support element actuators comprised in the support element actuator assembly, the one of the support element actuators being configured to actuate the respective support element) to move the respective support element to the new location. ln doing so continuously and _ 16 _ simultaneously with detecting the position of the feet of the user while the respective foot of the user is not in contact with the respective support element, the respective support element is continuously moved such that that respective support element is located underneath the foot of the user. When the user moves the respective foot back down and makes contact with the respective support element, the controller proceeds with determining the velocity profile for the respective support element based on the force and / or torque exerted by the respective foot of the user on the respective support element. ln some examples, when the user is running or walking, one foot of the user is in contact with its respective support element while the other foot is not in contact with its respective support element. Thus, one support element is in tracking mode to follow the foot of the user that is not in contact with that support element, while the other support element is in surface simulation mode to simulate the movement resulting from the force and / or torque exerted by the user on the surface embodied by the support element. In other cases, for example when the user is standing still, both feet are in contact with the support elements, and so both support elements are in surface simulation mode. When standing perfectly still, the support elements also remain stationary. However, typically some force and / or torque is exerted by the user on the support elements even when standing still. ln such cases, the support elements are moved slightly in accordance with the determined velocity profiles, thereby providing the necessary haptic feedback to the user to simulate the slight movements in the limited three degrees of freedom. For example, when standing still on both feet and slightly leaning forwards, in the real world this would result in the full body of the user being at a slight angle with respect to the floor. Thus, the reference frame is the floor, which is fixed. Since the harness is arranged to limit the movement of the user, for example at the waist of the user, the user is held stationary at a part of their body. Thus, when leaning forwards, that part of the user (for example the waist of the user) is held at a fixed location and, for the purpose of the intended movement of the user (leaning forward) acts as the reference frame. Thus, instead of the user being at an angle with respect to the floor (i.e., the body moving to create an angle with the floor), the floor (embodied by the two support elements) is moved such that the angle of the body with respect to the floor is simulated. Practically, in this example, both support elements are moved backwards as a result of the forces being exerted by the user on the support elements such that the leaning movement is simulated by the device. ln yet other cases, for example atsome point while running orjumping, both feet are not in contact with their respective support element. Thus, in such cases, both support elements are in tracking mode until one or both feet make contact again with their respective support element. _ 17 _ In a variant of this embodiment, the position sensor is further configured to determine the rotation of both feet of the user around the z-axis of the imaginary system of orthogonal axes and to generate respective position sensor signals representative of said rotation of each foot of the user. In this variant, each support element comprises a rotational actuator configured to rotate the respective support element around the z-axis of the imaginary system of orthogonal axes; In this variant, the controller is further configured to receive, from the position sensor, the respective foot rotation position sensor signals; to, in case that it is determined that the foot of the user is not in contact with the support element, control a respective rotational actuator to rotate a respective support element around the z-axis of the imaginary system of orthogonal axes such that the rotation of the support element around the z-axis of the imaginary system of orthogonal axes corresponds to the rotation of a respective foot of the user around the z-axis of the imaginary system of orthogonal axes. In this way, it is ensured thatwhen the user moves the respective foot back down after not being in contact with the respective support element, that also the orientation of the respective support element within the xy-plane (i.e., the rotation of the respective support element around the z-axis) is such that the foot of the user is fully supported by the respective support element once the foot of the user makes contact with the respective support element. In an embodiment, the force / torque sensor is arranged inside the support element such that the force and / or torque exerted by the foot of the user on the support element is transmitted to the force / torque sensor. In this embodiment, the force / torque sensor is configured to directly measure the forces exerted by a respective foot of the user on a respective support element. For example, in case the support element is a footplate, the force / torque sensor is arranged directly underneath the surface of the footplate on which the foot of the user rests. For example, the force / torque sensor is a 6 degrees of freedom sensor that allows force and torque measurement in three mutually perpendicular axes, such as for example the commercially available K6D110 sensor manufactured by ME-Meßsysteme GmbH. In an alternative embodiment, the force / torque sensor is arranged inside the harness such that the force and / or torque exerted by the user on the harness is transmitted to the force / torque sensor. In this alternative embodiment, the force / torque sensor is configured to determine the force and / or torque exerted by the foot of the user on the support element by inverting the direction of the force and / or torque exerted by the user on the harness. Thus, the force exerted by the foot of the user on the support element is measured by the force / torque sensor indirectly. _ 18 _ Since the harness limits or blocks the movement of the user in the three degrees of freedom, when the user attempts to move in those three degrees of freedom, a force is exerted on the harness which is proportional with the intended movement of the user. This force is identical to but opposite to the force exerted by the foot of the user on the support element. This alternative placement of the force / torque sensor offers a cost-effectiveway of determining the force and / or torque exerted by the foot of the user on the support element. In an embodiment, the controller is configured to determine the velocity profile for the support element by calculating the acceleration for the support element as a function of the determined force and / or torque exerted by the foot of the user on the support element in the limited three degrees offreedom of movement, the mass of the user, and the rotational inertia of the user; and integrating the acceleration for the support element over time to determine the velocity profile for the support element. Thus, the calculated acceleration of the support element is dependent on the determined force exerted by the foot of the user on the support element in the translational direction for the x- and y-axis (forward and sideways movement), as well as the rotation along the z-axis (yaw). Further, the calculated acceleration of the support element is dependent on the mass and the rotational inertia of the user, as it is the case in the real world: a heavier object requires more force to accelerate. The mass and rotational inertia of the user is for example measured at the moment the user first places their feet on the support elements (i.e., at the start of using the device). ln other examples, the mass and rotational inertia is provided by the user as an input to the device. ln yet other examples, the mass and / or rotational inertia is estimated. For example, the rotational inertia of the user is estimated by considering the user as a cylindrical body with a certain height corresponding to the height of the user. In a variant of this embodiment, the controller is configured to determine the velocity profile for the support element by: calculating the acceleration a for the support element by using formula a=F . m, wherein F is the determined force exerted by the foot of the user on the support element in the xy-plane of the imaginary system of orthogonal axes and m is the mass of the user; calculating the angular acceleration or for the support element by using the formula d=T . I, wherein T is the determined torque exerted by the foot of the user on the support element about the z-axis of the imaginary system of orthogonal axes and lis the rotational inertia of the user; and integrating the acceleration for the support element and the angular acceleration for the support element over time to determine the velocity profile for the support element. _ 19 _ In this variant, the implementation of the determination of the velocity profile for the support element is described by the following equations: (1) F .m = a (2)v=v+a°öt (3) T ° l = q (4)w=w+d°öt where: F is the determined force exerted by the foot of the user on the support element in the xy-plane of the imaginary system of orthogonal axes , m is the user mass, a is the acceleration for the support element, v is the current (linear) velocity, for the support element v is the updated (linear) velocity for the support element, or is the angular acceleration for the support element; T is the determined torque exerted by the foot of the user on the support element about the z-axis of the imaginary system of orthogonal axes, I is the rotational inertia of the user, and 6 is the step size of the algorithm, i.e., the duration in between computation steps. The step size is typically expressed in milliseconds, and an appropriate step size is chosen to ensure that the velocity of the support element is smoothly updated such that the movement of the user can be accurately simulated. The equations are based on Newtonian dynamics, in particular Newtons second law of motion. They result from the observation that the motion of a person is the result of the force exerted on the surface on which the user is standing, which results in an acceleration of the person with respect to the surface. The device, however, constrains the movement of the user in the limited three degrees offreedom of movement. Therefore, the user remains stationary in the degrees offreedom of movement that are constrained and simulated by the device. ln other words, the user is the reference frame for the movement to be simulated. Thus, it is not the acceleration of the user with respect to the floor that is computed, but rather the acceleration of the floor (i.e., the one or both support elements) with respect to the user. In a further variant of this embodiment, a variant of the equations described above are used, described below: (1) F ° K °m = a (2)v=C°v+a°öt (3) T ° K ° l = q (4)w=C°w+d°öt where K is a correction factor on the inertia, and C the damping factor on the velocity. It was discovered that a value for K and C close to and below 1 ensure a fast response timewhen starting movement of the support elements, lower resonance effects in the support elements, and less micro-movements of the support elements. ln some cases, the values K and C are functions of the current velocity v, i.e., the values K and C change based on the current velocity v. This variant is identical to the previous variant if K and C are equal to 1. -20- By choosing appropriate values for K and C, a more accurate and pleasant simulation of movement is provided. In an embodiment, the force / torque sensor is further configured to determine the force exerted by the foot of the user on the support element along the z-axis and to generate a vertical force / torque sensor signal representative of said force; and the controller is configured to receive, from the force / torque sensor, the vertical force / torque sensor signal and to determine the mass of the userm based on the vertical force / torque sensor signal. In this embodiment, the force / torque sensor acts as a scale for weighing the user. In that case, the mass of the user can be determined by the formulam = %, where 9 is the acceleration due to gravity. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described below with reference to the figures. These figures serve as examples to illustrate the invention and will not be construed as limiting the scope of the claims. In the different figures, like features are indicated by the like reference numerals. In the figures: Fig. 1 schematically shows the device according to an embodiment of the invention. Fig. 2 schematically shows the device according to an embodiment of the invention in use. Fig. 3 schematically shows a detailed view of the movement-limiting device of the device according to an embodiment of the invention. Fig. 4 schematically shows an exploded view of a footpad of the device according to an embodiment of the invention. Fig. 5 schematically shows an exploded view of the first arm and the second arm of the device according to an embodiment of the invention. DETAILED DESCRIPTION Fig. 1 schematically shows the locomotion simulation device 100 according to an embodiment of the invention. A system of orthogonal axes is defined with three dimensions: x, y, and 2. The z-axis corresponds to vertical. The xy-plane, then, corresponds to the horizontal plane. A stationary element 101 provides for a fixed reference point to which the other components of the device 100 are connected. The stationary element 101 is for example attached to the surface on which the device 100 rests using bolts. Additionally or alternatively, _ 21 _ the stationary element 101 is attached to a metal baseplate 110 of the device which is placed on the surface on which the device 100 rests. The metal baseplate 110 is for example provided with a layer that prevents the device 100 from sliding across the surface, for example wherein the layer is a rubber layer. The metal baseplate 110, as shown in figures 1 and 2, comprises a rectangular part extending from the stationary element 101 and two semi-circles on either side of the rectangular part. The metal baseplate 110 for example corresponds to the movement envelope of the support element within the xy-plane, which movement envelope corresponds to the expected walking envelope of the user of the device. However, the metal baseplate 110 is optional: the device can also be placed directly on an appropriate surface. The device 100 comprises a support element 102. The support element 102 is arranged to support a foot of a user of the device 100. In the figures, the support element 102 is a footpad which supports exactly one foot of the user. In this case, a single foot of the user is supported by a single support element 102. The support element 102 can alternatively comprise a plurality of smaller elements, such as rollers or moveable plates. However, as for the embodiments shown in the figures, the terms footpad and support element are used interchangeably. To use the device, the user initially places their foot on the support element 102. While in use, the foot of the user is either supported by the support element 102 or is lifted off the support element 102. When the foot of the user is lifted off the support element 102, the foot of the user is above the support element 102 in the z-direction. The support element 102 is actuated within the xy-plane defined by the x-axis and the y- axis by a support element actuator assembly which comprises a support element actuator 103. The support element actuator 103 comprises a first arm 104 and a second arm 105. The first arm 104 has a first end hinged to the stationary element 101 at a first hinge 106. Thus, the first arm 104 is pivotable about the first hinge 106 with respect to the stationary element 101. The first arm 104 has a second end hinged to the second arm 105 at a second hinge 107. Thus, the second arm 105 is pivotable about the second hinge 107 with respect to the first arm 104. In other words, the second arm 105 is attached at one of its ends to the first arm 104 at the end of the first arm 104 which is opposite the first hinge 106. The attachment point between the first arm 104 and the second arm 105 is defined by the second hinge 107. The support element 102 is provided at the second end of the second arm 105, le., the end of the second arm 105 opposite the second hinge 107. This end of the second arm is supported on the baseplate 110 by a wheel which is rotatable around the z-axis. The support element actuator 103 further comprises a first actuator 108 and a second actuator 109. The first actuator 108 and second actuator 109 are rotary actuators, for example servomotors. The first actuator 108 is arranged and configured to rotate the first arm 104 around the first hinge 106. The second actuator 109 is arranged and configured to rotate the second arm 105 around the second hinge 107. _ 22 _ The support element actuator 103 thus corresponds to aSCARA robot by virtue of its jointed two-link arm layout. Said layout defines a motion envelope of the support element 102 within the xy-plane. In other words, the extent of motion of the support element 102 within the xy- plane is defined by the support element actuator 103. The minimum and maximum angle of the first arm 104 around the first hinge 106 and the minimum and maximum angle of the second arm 105 around the first hinge 106 are chosen in function of the desired extent of motion of the support element 102. In use, the support element 102 is moveable to any position at which the foot of the user may be positioned. Said extent of motion is limited, because the movement of the user is limited by a harness of the device (not shown in Fig. 1, see for example Fig. 2 which shows harness 202) which is supported by the stationary element 101. For example, the harness holds the user, or part of the user such as the waist of the user, at a fixed location with respect to the stationary element 101. Therefore, the extent of motion of the feet of the user is also limited, in practice by the length and the extent of motion of the legs of the user. This extent of motion is defined by an imaginary circle or oval in the xy-plane with as its centre point the user of the device and is also called the walking envelope of the user. For example, the maximum step length is set at 1500mm. When measured from the stationary element 101 forwards in the x-direction, the centre of the circle is at x = 1000mm, which means that the most rearward point of the support element 102 is atx = 250mm and the most forward point is atx = 1750mm. The length of the first arm 104 is for example 1000mm and the length of the second arm 105 is for example 950mm. The dimensions of the support element 102 are chosen such that the support element 102 is capable of supporting the foot of the average user; for example, the width (i.e., the dimension along the y-axis) of the support element 102 is 135mm and the length (i.e., the dimension along the x-axis) of the support element 102 is for example 350mm. In this example, to achieve the required extent of motion of the support element 102, the minimum and maximum pivot angle of the first arm 104 about the first hinge 106 are chosen at around -20° and 75°, respectively. The minimum and maximum pivot angle of the second arm 105 about the first hinge 106 are chosen at around 15° and 130°, respectively. Other values of the minimum and maximum angle of the first arm 104 and second arm 105 are possible, depending on the desired step length as well as the length of the first arm 104 and the second arm 105. The device further comprises a force / torque sensor 112 which is arranged inside of the support element 102. The force / torque sensor 112 is arranged and configured to determine the force and / or torque exerted by the foot of the user on the support element 102 in three degrees of freedom of movement which are limited by the harness: translation along the x- axis of the imaginary system of orthogonal axes, translation along the y-axis of the imaginary system of orthogonal axes, and rotation around the z-axis of the imaginary system of -23- orthogonal axes. The force / torque sensor 112 is further configured to generate a force / torque sensor signal representative of said force and / or torque and to provide said force / torque sensor signal to the controller 111 of the device. By virtue of the force / torque sensor 112 being arranged inside of the support element 102, the force and / or torque exerted by the foot of the user on the support element 102 is sensed by the force / torque sensor 112 as it is transmitted through the surface of the support element 102 which is in contact with the foot of the user. A detailed view of the support element 102 and the force / torque sensor 112 arranged therein is shown in Fig. 4. In use of the device, the user is standing on the support element 102 and thus one of the users feet is supported by the support element 102. Therefore, the foot of the user exerts a force on the support element 102 which is measured by the force / torque sensor 112. In case the user is completely at rest, the force is directed downwards, i.e., in a downwards direction along the z-axis. The force exerted in this way is proportional with the weight of the user. When the user is intending to move in the xy-plane, the foot of the user exerts a force which is directed in the opposite direction to the direction in which the user intends to move. In the real world, when a person intends to move forward, a force which is directed backwards is exerted on the surface on which that person stands. The surface remains stationary and thus, as a result of the force exerted by the person on the surface, the surface provides a reactionary force opposite to the force exerted by the person which propels the person forwards. The device simulates such movement of the user by limiting the movement of the user in the three degrees offreedom mentioned above. Thus, instead of the surface remaining stationary, it is the user that remains stationary and thus the user functions as the reference point in relation to which the surface, embodied by the support element 102, is moved. When the force / torque sensor 112 measures a force in the backwards direction (i.e., along the x-axis towards the stationary element 101), then, just as in the real world, the user intends to move forward. However, since the movement of the user is limited in the x-direction by the harness, the user cannot move forward. lnstead, the support element 102 is moved backward proportional to the force that the user exerts on the support element 102. The device supports all movement in the xy-plane, i.e., forward / backward and leftward / rightward, as well as turning motions around the z-axis. To move the support element 102 appropriately, the controller determine a velocity profile for the support element 102 within the xy-plane of the imaginary system of orthogonal axes based on the force / torque sensor signal that it received from the force / torque sensor 112. The velocity profile is determined by calculating the (linear and rotational) acceleration of the support element 102 as a function of the determined force and / or torque exerted by the foot of the user on the support element 102 in the limited three degrees of freedom of movement, the mass of the user, and the rotational inertia of the user. The acceleration of the foot of the user is integrated over time to determine the (linear and rotational) velocity of the support element _ 24 _ 102. The mass and the rotational inertia of the user is for example determined when starting to use the device in a calibration step: in such a step, for example, the user remains stationary on the support element 102 and the downwards force exerted by the foot of the user on the support element 102 is used to calculate the mass of the user. Alternatively, the mass and / or the rotational inertia of the user is / are provided as a value to the device 100, for example to the controller 111. The controller 111 is configured to control the support element actuator 103 to actuate the support element 102 in accordance with the determined velocity profile for the support element 102 such that the support element 102 moves within the limited three degrees of freedom. The main equation governing the motion of theSCARA robot, embodied by the support element actuator 103 is: [M11 M12I_\QAI+[C11 C12]_[wAl:lT / 1] M21 M22 w'B C21 C22 (UB TB where M indicate the inertial forces, C the Coriolis forces, and T the torques at hingeA (i.e., hinge 106) and hinge B (i.e., hinge 107). The values ofM and C are chosen based on known methods in the art forSCARA control. This control scheme allows for direct feedback to the user by the near-instantaneous movement of the support element 102. This control scheme, called torque control in the art is one option of controlling theSCARA robot arms. Alternatively, a variable frequency drive is inserted between the controller 111 and the support element actuator 103. The controller 111 instructs the variable frequency drive to rotate the motor at a particular speed; the variable frequency drive in turn adjusts the torque dynamically to reach that speed. Said variable frequency drives are known in the art. The resulting velocity of the support element 102 is thus proportional to the force exerted by the foot of the user on the support element 102. Similarly, the resulting velocity of the support element 102 is proportional to the velocity of the userwhich would be the result of the user moving in the real world as a result of exerting thatsame force on the surface on which the user is standing. Thus, the device 100 simulates the locomotion of the user as a result of the force exerted by the foot of the user on the support element 102, while limiting the movement of the user. Thus, the user of the device has the sensation of moving as they would expect in the real world, while remaining (near) stationary. In Fig. 1, only a single support element 102 is shown that is arranged to support a foot of the user. Fig. 2 schematically shows the device according to an embodiment of the invention in use, wherein two support elements 102 are arranged to each support a foot of the user. In this embodiment, the support element actuator assembly comprises two support element actuators 103, each support element actuator 103 being configured to actuate a distinct support element -25- 102 within the xy-plane of the imaginary system of orthogonal axes. Two force / torque sensors 112 are each configured to determine the force and / or torque exerted by the foot of the user on a distinct footpad 102 in the limited three degrees of freedom of movement and to generate a force / torque sensor signal representative of said force and / or torque. The controller 111 is configured to receive the force / torque sensor signal from each force / torque sensor 112, to determine a velocity profile for each support element 102 within the limited three degrees of freedom based on said force / torque sensor signals and to control the support element actuators 103 to move each respective support element 102 in accordance with the velocity profile. In the figure, the user of the device is shown with one foot of the user being in contact with its respective support element 102, while the other foot of the user is located above its respective support element 102. Thus, the user is in the middle of a stepping or running movement. Atsome point, it can be expected that the left foot of the user will make contact with its respective support element 102 again, while the right foot of the user will break contact with its respective support element 102. The device comprises a movement-limiting device 201 which comprises the stationary element 101 and the harness 202 arranged to limit the movement of the user of the device in the three degrees offreedom of movement thatwere already mentioned (translation along the x-axis and y-axis, and rotation around the z-axis). The harness 202 is supported by the stationary element 101. As seen in the figure, a vertical beam of the stationary element 101 extends from a base plate of the stationary element 101. The harness 202 is supported by this vertical beam of the stationary element 101. The user is, during use of the device 100, the user is secured within the harness 202, for example using one or more straps. The harness 202 is arranged to allow movement of the user in the degrees of freedom of movement other than the limited three degrees of freedom of movement. In particular, the harness 202 allows translation of the user on the z-axis, as well as rotation around the x-axis (roll) and rotation around the y-axis (pitch). The movement-limiting device 201 is shown in more detail in Fig. 3. The harness 202 is worn on the torso of the user and the harness 202 is arranged to limit the movement of the torso of the user in the limited three degrees offreedom of movement. In particular, the harness 202 is worn on the waist of the user and the harness is arranged to limit the movement of the user at the waist of the user in the limited three degrees offreedom of movement. The harness is optionally arranged to block the movement of (parts of) the torso of the user in the three degrees of freedom of movement, although slight movements of the user in the three degrees of movement due to slack within the harness 202 may also be possible. The device comprises a position sensor 203. The position sensor 203 is a camera which is configured to detect the position of the feet of the user. For example, the camera _ 26 _ comprises or is connected to an object detection module which is configured to detect the position of the feet of the user. The camera provides a series of images to the object detection module. In some cases, the camera is configured to detect the position of the feet of the user within the xy-plane. In other cases, the camera is configured to detect the position of the feet of the user within 3D-space. Thus, as the user moves their feet, the camera and / or the object detection module provides a foot position sensor signal which is representative of the position of the foot of the user within the xy-plane of the imaginary system of orthogonal axes and / or along the z-axis of the imaginary system of orthogonal axes. The controller is configured to determine whether each foot of the user is in contact with its respective support element 102. Said determination is based, for example, on the force / torque sensor signal received from the force / torque sensor 112 of each of the support elements 102: if the force / torque sensor signal represents a force of (essentially) zero, then the controller 111 determines that the respective foot of the user is not in contact with the respective support element 102. If the force / torque sensor signal represents a non-zero force, then the controller 111 determines that the respective foot of the user is in contact with the respective support element 102. Alternatively or additionally, the determination whether each foot of the user is in contact with its respective support element 102 is for example based on the foot position sensor signal received from the position sensor 203. If said foot position sensor signal represents a gap in-between the foot of the user and its respective support element 102, then the controller 111 determines that the respective foot of the user is not in contact with the respective support element 102. If said foot position sensor signal represents (essentially) no gap in-between the foot of the user and its respective support element 102, then the controller 111 determines that the respective foot of the user is in contact with the respective support element 102. The controller 111 switches between two modes of operation based on the determination whether each foot of the user is in contact with its respective support element 102: when the foot of the user is in contact with its respective support element 102, the controller is configured to control said support element 102 in surface mode, also called acceleration mode, wherein the surface on which the user is moving is simulated as explained above: the force exerted by the foot of the user on the support element 102 is determined, a velocity profile for the support element 102 is determined, and the footplate 102 is moved (while supporting the foot of the user) in accordance with said velocity profile. When the foot of the user is not in contact with its respective support element 102, the controller is configured to control said support element 102 in following mode, also called tracking mode, wherein the support element 102 is moved to the position of the foot of the user within the xy-plane. Thus, as a result, the support element 102 follows the foot of the user while the foot of the user is located above the support element 102. Therewith, the support element -27- 102 is at the location of the foot of the user and will therefore support the foot of the user when the user places their foot back down. As a result, the user gets the impression of walking on a continuous surface, because they are supported by said surface embodied by the support element 102 when placing their foot back down. In some examples, the position sensor 203 is configured to determine the position of a portion of the foot of the user, such as the tip or the heel of the foot of the user. The foot portion position sensor signal generated by the position sensor 203 is representative of said position of the portion of the foot of the user. In such an example, the controller is configured to move the respective support element 102 within the xy-plane such that a portion of the respective support element 102 corresponding to the portion of the foot of the user is moved to the location of the portion of the foot of the user. For example, if the position sensor 203 is configured to determine the position of the tip of the foot of the user, then the controller 111 is configured to move the tip of the respective support element 102 to the detected position of the tip of the foot of the user. The user in the figure is wearing a virtual reality headset, which means that the user is immersed in a virtual or mixed reality world. Therefore, the user has limited or no visibility of the real world and thus is (virtually) unaware of the locomotion simulation device 100. lnstead, the virtual world is updated while locomotion of the user is being simulated. A forward step taken by the user, for example, results in the users avatar in the virtual world also taking a virtual step forward. Therewith, a realistic movement experience in the virtual world is provided by the locomotion simulation device 100. Fig. 3 schematically shows a detailed view of the movement-limiting device 201 of the device 100 according to an embodiment of the invention. The movement-limiting device 201 comprises a harness 202 which is supported by the stationary element 101. The height of the harness 202 is fixed, for example by suspending the construction which attaches the harness 202 to the stationary element 101 from a cable: said suspending prevents the movement-limiting device 201 from moving up or down. The user takes place inside of the harness 202 by placing the harness 202 securely around their waist. In this manner, the harness 202 limits the movement of the waist of the user in three degrees of freedom: forward and backward movement, i.e., movement along the x-axis (also known as translation T(x) along the x-axis); left and right movement, i.e., movement along the y-axis (also known as translation T(y) along the y-axis); and rotation around the vertical, i.e., rotation around the z-axis (also known as rotation R(z) around the z-axis). In particular, for rotation around the z- axis to be limited, in some examples the harness 202 further comprises a belt which is tightened around the waist of the user. -28- The harness 202 allows (limited) movement in the degrees offreedom other than the limited three degrees of freedom. The harness 202 is vertically slidable along bars, which thus allows for translation T(z) along the z-axis, i.e, up-and-down movement of the user along the z- axis. Said movement allows the user tojump or kneel down. The harness 202 is further rotatable around the x-axis, which thus allows for rotation R(x) around the x-axis, e.g., for the user to rotate their hips. Further, the harness 202 allows for limited tilt of the pelvis (i.e., rotation R(y) around the y-axis). An alternative placement of the force / torque sensor 112, is to arrange the force / torque sensor 112 inside the harness 202 such that the force and / or torque exerted by the user on the harness 202 is transmitted to the force / torque sensor 112. The force / torque sensor 112 is configured to determine the force and / or torque exerted by the foot of the user on the support element 102 by inverting the direction of the force and / or torque exerted by the user on the harness 202. The force / torque sensor 112 for example comprises one or more strain gauges that measure deformations in the harness 202 as the user moves. Since the harness limits or blocks movement of the user in the limited three degrees of freedom, the movement of the user in those three degrees of freedom is partly or completely transferred to the harness 202. Therefore, these forces measured in the harness 202 can be used to represent the desired movement of the user in the three degrees of freedom. The forces measured in the harness 202 are related to the forces exerted by the feet of the user on the support elements 102: they are equal in magnitude, but opposite in direction. Fig. 4 schematically shows an exploded view of a footpad of the device according to an embodiment of the invention. In this embodiment, the support element actuator assembly comprises a rotational actuator403 which is embedded within the second arm 105 and is configured to rotate the support element 102 around the z-axis of the imaginary system of orthogonal axes (i.e., rotation R(z)). In other words, the support element 102 is rotatably coupled to the end of the second arm 105 opposite the second hinge 107 via the rotational actuator 403. As shown in the figure, the rotational actuator 403 is mechanically connected to the footplate 102 using a belt-and-pulley system. Alternatively, the rotational actuator 403 is placed directly within the axis of rotation of the footplate 102. For example, the rotational actuator 403 is a servomotor that is directly connected, optionally via a gearbox, to the rotation axis of the footplate 102. The rotation axis is optionally further provided with an optical encoder to provide feedback about the absolute angular position of the footplate 102. The rotational actuator 403 is used for two purposes: one is to simulate rotations of the user while the foot of the user is supported by the footplate 102, the other is to rotate the -29- footplate 102 while the foot of the user is not in contact with the footplate 102 such that the rotation of the footplate 102 matches the rotation of the foot of the user. To simulate rotations of the user while the foot of the user is supported by the footplate 102, the force / torque sensor 112 is configured to measure the torque exerted by the foot of the user about the z-axis on the footplate 102. Said torque is a result of the user intending to rotate: a clockwise torque indicates that the user intends to rotate counterclockwise, while a counterclockwise torque indicates that the user intends to rotate clockwise. Since the rotation of the user around the z-axis is limited by the harness, the actual rotation that the user intends cannot be completed: instead, the feet of the user are rotated in the opposite direction to which the user intends to rotate their body to simulate said rotation. So, the controller 111 is configured to control the rotational actuator to rotate the footplate 102 around the z-axis in correspondence with the determined torque exerted by the foot of the user on the footplate 102. To rotate the footplate 102 while the foot of the user is not in contact with the footplate 102 such that the rotation of the footplate 102 matches the rotation of the foot of the user, the position sensor203 is further configured to determine the rotation of the foot of the user around the z-axis of the imaginary system of orthogonal axes and to generate a foot rotation position sensor signal representative of said rotation of the foot of the user around the z-axis of the imaginary system of orthogonal axes. The controller 111 is configured to control the rotational actuator to rotate the support element around the z-axis of the imaginary system of orthogonal axes such that the rotation of the support element around the z-axis of the imaginary system of orthogonal axes corresponds to the rotation of the foot of the user around the z-axis of the imaginary system of orthogonal axes. Fig. 5 schematically shows an exploded view of the first arm 104 and the second arm 105 of the device 100 according to an embodiment of the invention. The first actuator 108 is arranged to directly pivot the first arm 104 about the first hinge 106. The second actuator 109 comprises a rotary motor and a chain-and-pulley system embedded within the first arm 104 to transfer the rotation of the rotary motor to the second arm 105 in order to pivot the second arm 105 about the second hinge 107. Alternatively, a belt can be used instead of a chain or any other element that allows transferring of the rotation from the second actuator 109 to the second hinge 107. The rotational actuator403 is configured to rotate the support element 102 around the z-axis. Thus, due to the three actuators 108, 109, and 403 shown in the figure, movement of the support element 102 within the xy-plane and around the z- axis is supported. The controller 111 is connected to the first actuator 108, the second actuator 109 and the rotational actuator 403. The controller 111 is configured to instruct the actuators to which it is -30- connected to move the support element 102 in accordance with a velocity profile for the support element 102 which is determined from the force and / or torque with which the foot of the user interacts with the support element 102 in the three degrees of freedom. As required, this document describes detailed embodiments of the present invention. However, it must be understood that the disclosed embodiments serve exclusively as examples, and that the invention may also be implemented in other forms. Therefore, specific constructional aspects which are disclosed herein should not be regarded as restrictive for the invention, but merely as a basis for the claims and as a basis for rendering the invention implementable by the average skilled person. Furthermore, the various terms used in the description should not be interpreted as restrictive but rather as a comprehensive explanation of the invention. The word "a" used herein means one or more than one, unless specified othenNise. The phrase "a plurality of" means two or more than two. The words "comprising" and "having" do not exclude the presence of more elements. Reference figures in the claims should not be interpreted as restrictive of the invention. Particular embodiments need not achieve all objects described. The mere fact that certain technical measures are specified in different dependent claims still allows the possibility that a combination of these technical measures may advantageously be applied. C O N C L U S l E S 1] Locomotiesimulatieinrichting (100), waarbij een denkbeeldig systeem van orthogonale axes comprising an x-axis, a y-axis, and a z-axis are defined, where each axis has two defines degrees of freedom, where the two degrees of freedom are translation along and rotation about the as are; the locomotive simulation device comprising: ° a movement-restricting device (201), comprising: - a harness (202) designed to restrict the movement of a user of the to restrict the arrangement into three degrees of freedom of movement, whereby the restricted three degrees of freedom translation along the x-axis of the imaginary system of orthogonal axes, translation along the y-axis of the imaginary system of orthogonal axes and rotation about the z-axis of the imaginary system of orthogonal axes are; - a stationary element (101) that supports the harness; ° a support element (102) that is set up to support a user's foot to support; . a support element actuator assembly (103, 403) configured to the support element to drive in the limited three degrees of freedom; ° a force / torque sensor (401) configured to determine the force and / or torque exerted by the user's foot on the support element in the limited three degrees of freedom and to generate a force / torque sensor signal that is representative of the force and / or the torque; ° a controller (111) configured to: - to receive the force / torque sensor signal from the force / torque sensor that is representative of the force and / or torque with which the user's foot interacts with the support element in the limited three degrees of freedom of movement; - to determine a velocity profile for the support element within the limited three degrees of freedom based on the force / torque sensor signal; - to control the support element actuator assembly to the support element to drive in accordance with the specified speed profile, so that the support element moves within the limited three degrees of freedom. 2] Device according to claim 1, where the harness is designed to allow movement of the to allow the user in degrees of freedom that differ from the limited three degrees of freedom of movement. 3] Arrangement in accordance with one of the preceding claims, whereby: ° the force / torque sensor is configured to: - to determine the force exerted by the user's foot on the support element is exercised within an xy-plane of the imaginary system of orthogonal axes; and - to determine the torque exerted by the user's foot on the support element is exercised around the z-axis of the imaginary system of orthogonal axes; ° the controller is configured to determine the speed profile for the support element at basis of the force exerted by the user's foot on the support element within the xy-plane of the imaginary system of orthogonal axes and based on the torque exerted by the user's foot on the support element around the 2- axis of the imaginary system of orthogonal axes. 4] Configuration in accordance with one of the preceding claims, whereby the harness is configured to be worn on the user's torso and where the harness is designed to to restrict the movement of the user's torso in the limited three degrees of freedom of movement. 5] Configuration in accordance with one of the preceding claims, whereby the harness is configured to restrict the movement of the user at the level of the user's waist in the limited three degrees of freedom of movement. 6] Configuration in accordance with one of the preceding claims, whereby the harness is configured to block the user's movement within the limited three degrees of freedom. 7] Arrangement in accordance with one of the preceding claims, whereby: ° the support element is a foot platform; ° the device further includes a position sensor (203) which is designed to determine the position of the user's foot within the xy-plane and optionally along the z-axis of the imaginary to determine system of orthogonal axes and to generate a foot position sensor signal that is representative of the position of the user's foot; ° the controller is further configured to: - to receive the foot position sensor signal from the position sensor; - based on the force / torque sensor signal and / or the foot position sensor signal to determine whether the user's foot is in contact with the supporting element; - if it is determined that the user's foot is not in contact with the support element, to control the support element actuator assembly to the support element to move within an xy-plane of the imaginary system of orthogonal axes towards the position of the user's foot; - if it is determined that the user's foot is in contact with the support element, to proceed with the steps of determining the speed profile for the support element and controlling the support element actuator assembly to the to move support element in accordance with the determined velocity profile. 8] Arrangement in accordance with claim 7, whereby: ° the position sensor is further configured to determine the position of a part of the foot of the user, preferably the tip or heel of the user's foot, within the xy-plane of the to determine an imaginary system of orthogonal axes and to a to generate a foot section position sensor signal that is representative of the position of the section of the user's foot; ° the controller is further configured to: - to receive the footrest position sensor signal from the position sensor; - if it is determined that the user's foot is not in contact with the support element, to control the support element actuator assembly to the support element to move within the xy-plane such that a part of the support element that corresponds with the part of the user's foot to the location of the part of the foot of the The user is moved. 9] Arrangement in accordance with one of claims 7-8, whereby: ° the position sensor is further designed to detect a rotation of the user's foot around to determine the z-axis of the imaginary system of orthogonal axes and to a to generate a foot rotation position sensor signal that is representative of the rotation of the foot of the user around the z-axis of the imaginary system of orthogonal axes; ° the support element actuator assembly includes a rotary actuator (403) which is arranged to the support element around the z-axis of the imaginary system of orthogonal to rotate axes; ° the controller is further configured to: - to receive the foot rotation position sensor signal from the position sensor; - if it is determined that the user's foot is not in contact with the support element, to control the rotational actuator to rotate the support element around the z-axis of to rotate the imaginary system of orthogonal axes such that the rotation of the support element around the z-axis of the imaginary system of orthogonal axes corresponds to the rotation of the user's foot around the z-axis of the imaginary system of orthogonal axes. 10] Arrangement in accordance with one of the preceding claims, whereby: ° the support element actuator assembly a first arm (104) and a second arm (105) includes; ° the first arm has a first end that is hinged to the stationary element at a first hinge (106); and a second end that hinges is connected to a first end of the second arm at a second hinge (107); ° The support element is provided on a second end of the second arm. 11] Configuration in accordance with claims 9 and 10, where the support element is rotatable connected to the second end of the second arm via the rotational actuator. 12] Arrangement in accordance with one of claims 10-11, whereby: ° the support element actuator assembly a first actuator (108) and a second actuator (109) includes; ° the first actuator is configured to pivot the first arm around the first hinge; ° the second actuator is configured to move the second arm around the second hinge swivel; ° the pivot of the first arm around the first hinge and the pivot of the second arm around the second hinge ensures that the support element moves within the xy-plane of the imaginary system of orthogonal axes. 13] Arrangement in accordance with one of the preceding claims, where the arrangement comprises: ° two support elements, where the support elements are foot platforms, and where Both foot platforms are designed to each accommodate a separate foot of the user. to support; ° two force / torque sensors, each configured to measure the force and / or torque determine that exercise is performed by the user's foot on a separate foot platform within the limited three degrees of freedom of movement and to a force / torque sensor signal generate that is representative of the power and / or torque; ° where the support element actuator assembly is configured to the foot platforms to drive in the limited three degrees of freedom; ° where the controller is configured to: - a force / torque sensor signal from each force / torque sensor received that is representative of the force and / or torque with which the foot of the user interacts with a respective foot platform in the limited three degrees of freedom of movement; - to determine a speed profile for each foot platform within the limited three degrees of freedom based on a force / torque sensor signal received from a force- / torque sensor; - to control the support actuator assembly to a respective to propel the foot platform in accordance with the specified speed profile so that it The respective foot platform moves within the limited three degrees of freedom. 14] Configuration in accordance with claim 13, where the velocity profile for each respectively foot platform is determined based on the force / torque sensor signal received from both force / torque sensors. 15] Arrangement in accordance with one of claims 13-14, whereby: ° The position sensor is designed to measure the position of both of the user's feet within to determine the xy-plane of the imaginary system of orthogonal axes and to to generate respective foot position sensor signals that are representative of the position of every foot of the user; ° the controller is further configured to: - to receive the respective foot position sensor signals from the position sensor; - based on the force / torque sensor signal and / or the respective foot position sensor signals to determine whether a respective foot of the user is in contact with a respective supporting element; - if it is determined that the respective foot of the user is not in contact with the respective support element, to control the support element actuator assembly to to move the respective support element within the xy-plane to the position of the respective foot of the user; - if it is determined that the respective foot of the user is in contact with the respective support element, to proceed with the steps of determining the velocity profile for the respective support element and the control of the support elements actuator assembly to move the respective support element in accordance with the specific speed profile. 16] Arrangement in accordance with one of claims 13-15, where the position sensor is further arranged for the rotation of both feet of the user around the z-axis of the imaginary to determine system of orthogonal axes and to respective position sensor signals generate that are representative of the rotation of each foot of the user; ° each support element comprises a rotational actuator configured to the respective to rotate a support element around the z-axis of the imaginary system of orthogonal axes; ° the controller is further configured to: - from the position sensor the respective foot rotation position sensor signals received; - if it is determined that the user's foot is not in contact with the support element, to control a respective rotational actuator to a respective to rotate a support element around the z-axis of the imaginary system of orthogonal axes so that the rotation of the support element around the z-axis of the imaginary system of orthogonal axes correspond to the rotation of a respective foot of the user around the z-axis of the imaginary system of orthogonal axes. 17] Configuration in accordance with one of the preceding claims, where the force / torque sensor is placed inside the support element so that the force and / or torque that the the user's foot is exerted on the support element, is transferred to the force / torque sensor. 18] Arrangement in accordance with one of claims 1-16, whereby: ° the force / torque sensor is placed inside the harness so that the force and / or the torque exerted by the user on the harness is transferred to the force / torque sensor; ° the force / torque sensor is designed to measure the force and / or torque exerted by the foot the force exerted by the user on the support element is determined by the direction of the to invert the force and / or the torque exerted by the user on the harness. 19] Configuration in accordance with one of the preceding claims, where the force / torque sensor includes a strain gauge. 20] Device in accordance with one of claims 7-19, where the position sensor is a camera and includes an object tracking module configured to identify the user's foot and to determine the position of the user's foot. 21] Configuration in accordance with one of the preceding conclusions, where the regulator is configured to determine the velocity profile for the support element by: ° to calculate the acceleration for the support element as a function of the determined force and / or the specific torque exerted by the user's foot on the support element is exercised within the limited three degrees of freedom of movement, the mass of the user, and the user's moment of inertia; and ° to integrate the acceleration for the support element over time to the to determine the velocity profile for the support element. 22] Configuration according to claim 21, where the regulator is configured to to determine the velocity profile for the support element by: ° to calculate the acceleration a for the support element using the formula a=F ° m, where F is the specific force exerted by the user's foot on the support element exercised in an xy-plane of the imaginary system of orthogonal axes and the mass of the user is; ° to calculate the angular acceleration or for the support element using the formula or = T ° I, where T is the specific torque exerted by the user's foot on the support element exercised around the z-axis of the imaginary system of orthogonal axes and I the moment of inertia of the user is; ° the acceleration for the support element and the angular acceleration for the support element to integrate over time to determine the velocity profile for the support element. 23] Arrangement in accordance with one of the preceding claims, whereby: ° the force / torque sensor is further configured to determine the force exerted by the foot force exerted by the user on the support element along the z-axis and to a vertical to generate a force / torque sensor signal that is representative of the force; ° the controller is designed to convert the vertical force / torque from the force / torque sensor to receive the sensor signal and to determine the mass of the user based on the vertical force / torque sensor signal.

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