CN217669394U - Human body wearing upper limb exoskeleton device for heavy load carrying - Google Patents

Abstract

The utility model discloses a human body dresses upper limbs ectoskeleton device for heavy load transport, adopt shoulder back plate device, width adjusting device, shoulder joint device and arm drive arrangement can realize following human arm and rotate, switch human arm strength to human back, adopt active mode, when lightening whole equipment quality, the degree of freedom distribution that is fit for human motion has, pressure and moment that the heavy object that the shoulder joint received when sharing human transport heavy object brought, be fixed with shoulder back plate revolute joint and shoulder revolute joint on the shoulder flitch, shoulder flitch symmetry is provided with two sets of width adjusting device, a set of shoulder joint device and arm drive arrangement are connected to every width adjusting device of group, can form double bracing auxiliary structure, realize carrying out the supplementary purpose of great strength when carrying out the heavy object to the workman, moreover, the steam generator is simple in structure, it is convenient to dress, helping hand-force when carrying the heavy object to the human body, reduce human shoulder mechanism damage, and has great significance.

Description

Human body wearing upper limb exoskeleton device for heavy load carrying

Technical Field

The utility model belongs to ergonomic engineering makes the field, is applied to needs such as cargo handling, medical care, logistics support and relies on the manpower to carry out object transport place, concretely relates to a human body dress upper limbs ectoskeleton device for heavy load transport.

Background

In some special workplaces it is necessary for people to lift, hold, carry or move heavy objects. The worker who performs this operation is at risk of increasing physical strength due to muscle damage, because of long-term high-intensity physical labor. A large number of facts indicate that frequent and long-term handling of heavy objects tends to increase the risk of injury to the shoulder muscles and lumbar strain of the worker.

The exoskeleton is a special device which can perfectly combine human intelligence with the exoskeleton device and has very wide application value: exoskeletons can generally be divided into two types, depending on the energy source: passive exoskeleton, active exoskeleton.

At present, a passive exoskeleton in China provides an upward supporting force for arms of a wearer through a mechanical structure, and therefore strength assistance for the arms of the wearer is achieved. However, when the arm of the human body has no heavy object and needs to move downwards, the human body is required to provide extra strength to counteract the upward thrust of the mechanical structure to the arm. Has the characteristics of small auxiliary force, low flexibility and poor man-machine cooperativity.

At present, the domestic active exoskeleton measures the motion condition of upper limbs of a human body through a sensor, and the control module drives a motor to drive arms of a wearer to move, so that the force assistance to the arms of the wearer is realized. However, the domestic upper limb active exoskeleton is driven by using the lack of freedom degree, and the flexibility is too low. It is difficult to meet the requirement of flexible movement of the upper limbs of the human body.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a human body dresses upper limbs ectoskeleton device for heavy load transport to overcome prior art's not enough.

A human body wearing upper limb exoskeleton device for heavy load transportation comprises a shoulder back plate device, a width adjusting device, a shoulder joint device and an arm driving device;

the shoulder backboard device comprises a shoulder attachment plate, a shoulder backboard rotating joint and a shoulder rotating joint are fixed on the shoulder attachment plate, two groups of width adjusting devices are symmetrically arranged on the shoulder attachment plate, and each group of width adjusting devices is connected with one group of shoulder joint devices and an arm driving device;

the width adjusting device comprises a back width adjusting mechanism and a shoulder width adjusting mechanism, the back width adjusting mechanism comprises a waist-shoulder cross rod, and one end of the waist-shoulder cross rod is rotatably connected with the shoulder-back plate rotating joint; the shoulder and back plate rotating joint comprises a shoulder cross rod, and one end of the shoulder cross rod is rotatably connected with the other end of the waist and shoulder cross rod;

the shoulder joint device comprises a universal joint motor connecting rod, and one end of the universal joint motor connecting rod is connected with the other end of the shoulder cross rod through a cross universal joint;

the arm driving device comprises a motor, the motor is fixed at the other end of the universal joint motor connecting rod through a motor mounting plate, an output shaft of the motor is fixed with an arm supporting plate, and the arm supporting plate and the shoulder flitch are both provided with a bandage.

Preferably, the device also comprises a height adjusting device, wherein the height adjusting device comprises a waist support rod and a waist positioning rod; one end of the waist support rod piece is sleeved with one end of the waist positioning rod piece, the other end of the waist support rod piece is fixed with a waist patch, and a fixing band is arranged on the waist patch; the shoulder back plate is fixed with a waist rotary joint, and the other end of the waist positioning rod piece is rotationally connected with the waist rotary joint.

Preferably, the shoulder back plate rotating joint and the shoulder rotating joint are both fixed at the lower end of the shoulder flitch through the shoulder back plate, a waist-shoulder rotating joint is fixed on the shoulder back plate, and the upper end of the shoulder flitch is connected with the waist-shoulder rotating joint through a waist-shoulder connecting shaft.

Preferably, one end of the waist-shoulder cross rod is rotatably connected with the shoulder-back plate rotating joint through a back adjusting connecting rod, the back adjusting connecting rod is vertically arranged, and the waist-shoulder cross rod is horizontally arranged.

Preferably, one end of the shoulder cross rod is rotatably connected with the shoulder width rotating joint through a shoulder adjusting connecting rod.

Preferably, the arm supporting plate is fixedly connected with an output shaft of the motor through a motor drive execution plate.

Preferably, a three-dimensional force sensor is arranged between the arm supporting plate and the motor-driven execution plate.

Preferably, a motor motion limiting groove is formed in the motor mounting plate, a limiting block is arranged on the motor drive execution plate, and the limiting block on the motor drive execution plate is limited by the motor motion limiting groove.

Preferably, the shoulder backboard, the shoulder flitch and the waist patch are all arc-shaped structures.

Preferably, the shoulder back plate rotating joint, the shoulder rotating joint and the shoulder width rotating joint can adopt bearing structures.

Compared with the prior art, the utility model discloses following profitable technological effect has:

the utility model provides a human body dresses upper limbs ectoskeleton device for heavy load transport, adopt shoulder back plate device, width regulation device, shoulder joint device and arm drive arrangement can realize following the rotation of human arm, hand over human arm strength to human back, adopt active mode, when lightening whole equipment quality, have the degree of freedom distribution that is fit for human motion, pressure and moment that the heavy object that receives when sharing human transport heavy object the shoulder joint brought, this application can realize the motion of human body in the heavy object transport process of bowing, six actions of satisfying the bending of human shoulder joint respectively, stretch, abduction, adduction, internal rotation, external rotation, helping hand when carrying the heavy object to the human body, reduce human shoulder mechanism damage, have important meaning.

Preferably, a shoulder back plate rotating joint and a shoulder rotating joint are fixed on the shoulder attachment plate, two groups of width adjusting devices are symmetrically arranged on the shoulder attachment plate, each group of width adjusting devices is connected with one group of shoulder joint devices and an arm driving device, a double-support auxiliary structure can be formed, the purpose of carrying out large strength assistance when a worker moves heavy objects is achieved, the structure is simple, and wearing is convenient.

Preferably, the height adjusting device is utilized, the gravity of the whole device can be distributed to the waist of a human body, and the gravity action of the shoulders is further reduced.

Preferably, adopt the motor as power original paper, can provide great strength for the wearer on the one hand supplementary, on the other hand is favorable to controlling, satisfies the needs of high follow-up nature.

Drawings

Fig. 1 is a schematic view of the overall structure of the upper limb exoskeleton device in the embodiment of the present invention.

Fig. 2 is a schematic view of an arm driving device according to an embodiment of the present invention.

In the figure, 1, a shoulder flitch, 2, a shoulder backboard, 3, a shoulder backboard rotating joint, 4, a shoulder rotating joint, 5, a back adjusting connecting rod, 6, a waist and shoulder bent pipe, 7, a waist and shoulder cross rod, 8, a shoulder width rotating joint, 9, a shoulder adjusting connecting rod, 10, a shoulder cross rod, 11, a cross universal joint, 12, a universal joint motor connecting rod, 13, a motor mounting plate, 14, a waist and shoulder connecting shaft, 15, a waist and shoulder rotating joint, 16, a waist rotating joint, 17, a waist positioning rod piece, 18, a waist supporting rod piece, 19, a waist positioning rod piece connecting joint, 20, a waist patch, 21, a driving motor, 22, a motor motion limiting groove, 23, a motor driving execution plate, 24, a three-dimensional force sensor and 25, an arm supporting plate.

Detailed Description

In order to make the technical solution of the present invention better understood, the technical solution of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts shall belong to the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, apparatus, article, or device that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or device.

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1, a human body wearing upper limb exoskeleton device for heavy load transportation comprises a shoulder backboard device, a width adjusting device, a shoulder joint device, an arm driving device, a height adjusting device and a swinging device;

the width adjusting device is arranged on the left side and the right side of the shoulder back plate device through the connection of a back adjusting connecting rod 5 and a shoulder rotating joint 4; when the device is worn by wearers with different shoulder widths, the device rotates around the shoulder rotating joint 4 and the shoulder width rotating joint 8 through the back width adjusting mechanism and the shoulder width adjusting mechanism, so that the width of the device is automatically adjusted, and the requirements of all shoulder width people are met. The shoulder joint device is connected with the shoulder cross bar 10 and the width adjusting device through a cross universal joint 11 and the width adjusting device. When the arm of the wearer swings, the shoulder joint device swings following the upper arm of the person. The arm driving device is connected with the motor driving execution plate 23 and the shoulder joint device through an output shaft of the motor 21. When the motor 21 moves along with the upper arm of the human body, the arm driving device works to push the arm of the human body to move through the arm supporting plate 25, and the purpose of assisting strength is achieved. The swinging device and the shoulder and back plate device are connected together through a shoulder and back plate rotating joint 3 and a waist and shoulder connecting shaft 14. When the waist of the wearer swings left and right, the waist shoulder rotary joint in the swinging device can rotate around the waist rotary joint, and then the shoulder back plate device is driven to rotate correspondingly, so that the whole left and right inclination of the equipment is realized. The height adjustment device and the swinging device are connected together by a waist rotary joint and a waist positioning rod 17. Through to the adjustment to aligning the hole position between height adjusting device, waist accent position member 17 and the waist bracing piece 18, realize the regulation of equipment overall height, satisfy different height crowds' use.

The shoulder backboard device comprises a shoulder pasting board 1, a shoulder backboard 2, a shoulder backboard rotating joint 3 and a shoulder rotating joint 4; the shoulder back plate 2 and the shoulder flitch 1 are connected through screws to form a stable bearing structure, the shoulder flitch 1 is an arc-shaped plate and is attached to the back of a human body, and a cushion layer is arranged on the shoulder flitch 1; the shoulder backboard rotary joint 3 is fixed on the shoulder backboard 2 through a screw or a bolt; the shoulder rotating joints 4 are fixed on the shoulder back plate 2 through screws or bolts, and two shoulder rotating joints 4 are symmetrically arranged on the shoulder back plate 2;

the width adjusting device comprises a back width adjusting mechanism and a shoulder width adjusting mechanism;

the back width adjusting mechanism comprises a back adjusting connecting rod 5, a waist and shoulder bent pipe 6, a waist and shoulder cross rod 7 and a shoulder width rotating joint 8; the back adjusting connecting rod 5 is rotatably connected with the shoulder rotating joint 4 on the shoulder backboard 2, one end of the waist-shoulder cross rod 7 is connected with one end of the back adjusting connecting rod 5 through the waist-shoulder elbow 6, when the whole equipment is vertically placed, the back adjusting connecting rod 5 is in a vertical state, the waist-shoulder cross rod 7 is in a horizontal state, the waist-shoulder elbow 6 is used as a connecting joint of the waist-shoulder cross rod 7 and the back adjusting connecting rod 5, and the waist-shoulder elbow 6 is respectively in threaded connection with the waist-shoulder cross rod 7 and the back adjusting connecting rod 5 or is integrally formed; the waist and shoulder cross bar 7 is used as a support bar for horizontal rotation, and the back adjusting connecting rod 5 is used as a horizontal rotating shaft; the other end of the waist-shoulder cross bar 7 is provided with a shoulder width rotating joint 8;

the shoulder width adjusting mechanism comprises a shoulder adjusting connecting rod 9 and a shoulder cross rod 10, the shoulder adjusting connecting rod 9 is rotatably connected with the shoulder width rotating joint 8, one end of the shoulder cross rod 10 is fixedly connected with one end of the shoulder adjusting connecting rod 9, and the shoulder width adjusting mechanism can be connected with a bent pipe or integrally formed.

The shoulder backboard rotary joint 3, the shoulder rotary joint 4 and the shoulder width rotary joint 8 can all adopt bearing structures, and the resistance of the whole equipment rotation is reduced.

The back width adjusting mechanisms are symmetrically arranged on the shoulder rotating joints 4 on the left side and the right side of the shoulder backboard device, each back width adjusting mechanism is provided with a group of shoulder width adjusting mechanisms, and the back width adjusting mechanisms are connected through the shoulder width rotating joints 8 on the back width adjusting mechanisms.

When people with different shoulder widths wear the equipment, the back width adjusting mechanism and the shoulder width adjusting mechanism respectively rotate around the shoulder rotating joint 4 and the shoulder width rotating joint 8 to drive the shoulder joint device to move, so that the relative distance between the motor mounting plates 13 on the left side and the right side is changed and is kept consistent with the shoulder width of a wearer.

The shoulder joint device comprises a cross universal joint 11, a universal joint motor connecting rod 12 and a motor mounting plate 13, wherein the cross universal joint 11, the universal joint motor connecting rod 12, the motor mounting plate 13 and a motor 21 form a three-degree-of-freedom mechanism which is used for replacing the internal rotation, external expansion, internal contraction and flexion and extension movements of the shoulder joint of a human body. One end of a cross universal joint 11 is fixedly connected with one end of a universal joint motor connecting rod 12 through a pin, the other end of the cross universal joint 11 is fixed at one end of a shoulder cross rod 10, a motor mounting plate 13 is fixed at the other end of the universal joint motor connecting rod 12, and a motor 21 is fixed on the motor mounting plate 13;

as shown in fig. 2, the arm driving device includes a motor 21, a motor movement limiting groove 22, a motor driving execution plate 23, a three-dimensional force sensor 24, and an arm supporting plate 25; the motor 21 is fixed on the motor mounting plate 12, the motor driving execution plate 23 is fixedly connected with an output shaft of the motor 21, the three-dimensional force sensor 24 is connected with the motor driving execution plate 23 through a screw, and the arm supporting plate 25 is connected with the three-dimensional force sensor 24 through a screw; the arm supporting plate 25 can be attached to the arm of a human body, supporting force is provided for the arm of the human body through driving of the motor, and adjustment within a wide angle range can be achieved. When the motor 21 drives the motor to drive the execution plate 23 to move, the arm supporting plate 25 pushes the arms of the human body to move up and down, and the arms of the upper limbs of the wearer are assisted by strength. In order to avoid the injury to the human body caused by the motor movement exceeding the physiological limit of the shoulder joint of the human body, the motor movement limiting groove 22 is arranged on the motor mounting plate 13, the limiting block is arranged on the motor driving execution plate 23, when the motor 21 drives the motor driving execution plate 23 to move to the limit position of the shoulder joint movement of the human body, the limiting block on the motor driving execution plate 23 is limited by the motor movement limiting groove 22, the motor driving execution plate 23 can be prevented from continuing to move by the motor movement limiting groove 22, the motor 21 is driven to stop passively, and the human body is prevented from being injured; the arm supporting plate 25 is provided with an arm fixing belt for fixing the arm supporting plate 25 and the arm of the human body.

The height adjusting device comprises a waist support rod 18 and a waist position adjusting rod 17; the waist support rod member 18 is sleeved with the waist position adjusting rod member 17, the waist support rod member 18 and the waist position adjusting rod member 17 are round pipes with different diameters and the same eyelet distribution, a waist support component lifting lug 19 is fixed at the lower end of the waist support rod member 18, the waist support component lifting lug 19 is fixedly connected to a waist patch 20 through screws, and the waist patch 20 is an arc-shaped plate and is attached to the waist of a human body. In practical use, the wearer can adjust the height of the wearing device by adjusting the length of the waist-adjusting rod 17 in the waist supporting rod 18; a waist rotary joint 16 is fixed on the shoulder back plate 2, and the waist rotary joint 16 is rotatably connected with one end of an adjusting rod 17.

All be provided with shoulder flitch 1 and waist paster 20 on the braces hole, not giving the braces structure in this application figure, shoulder flitch 1 and waist paster 20 are dressed on the human body through the braces, can adopt the knapsack braces structure, use with belly fixed band simultaneously together.

The swinging device comprises a waist and shoulder rotating joint 15, the waist and shoulder rotating joint 15 is fixed on the shoulder back plate 2, the shoulder flitch 1 is made of soft material, the upper end of the shoulder flitch 1 is connected with the waist and shoulder rotating joint 15 through a waist and shoulder connecting shaft 14, the shoulder flitch 1 is fixed with one end of the waist and shoulder connecting shaft 14, and the shoulder flitch 1 is rotated and can rotate relative to the shoulder back plate 2 through the waist and shoulder connecting shaft 14; the shoulder back plate 2 adopts an arc-shaped plate; when the waist of the wearer swings left and right, the mechanism can swing left and right along with the waist of the wearer and drive the shoulder backboard device to move correspondingly.

A specific work flow of a human body wearing upper limb exoskeleton device for heavy load carrying in a use process comprises the following steps:

a. bending the human body and carrying heavy objects. The cross universal joint 11, the universal joint motor connecting rod 12, the motor mounting plate 13 and the motor 21 rotate along with the shoulder joint of the human body in the process of bending the human body to carry heavy objects. Wherein two rotating shafts of the cross universal joint 11 rotate along with the shoulder joint of the human body, and the motor moves up and down according to the arm of the human body to provide strength for the arm of a wearer. The arm driving device lifts the arm of the wearer by driving the motor 21 to carry the heavy object.

b. The human body lifts up by carrying heavy objects. The downward pressure of the heavy object on the arm of the human body is transmitted to the shoulder cross bar 10 of the exoskeleton left-right width adjusting device through the arm driving device and the shoulder joint device, the shoulder cross bar 10 is subjected to downward load, and the force can be transmitted to the waist of the human body along the width adjusting device, the shoulder back plate device and the height adjusting device.

Each joint can adopt a bearing structure; the upper limb exoskeleton device is characterized in that a motor is an actual extension AK80-64 motor, so that the upper limb exoskeleton device is light in weight, convenient to carry and capable of reducing the mass of the whole device, the main body part of the upper limb exoskeleton device is made of carbon fiber materials, the weight of the whole device is not more than 10kg, the wearing requirements of people with different heights, weights and shoulder widths in all ages can be met, the upper limb exoskeleton device adopts the motor as a power element, on one hand, the motor can provide large force assistance for a wearer, on the other hand, the control is facilitated, and the requirement of high follow-up performance is met; the power supply is fixed on the shoulder backboard 2, and the power supply bin is arranged on the shoulder backboard 2 and used for fixedly mounting the power supply.

The device is simple in structure, the force sensor is used as a measuring device, when the arm of a wearer moves, the actual auxiliary force of the motor on the arm of the wearer is obtained through the force sensor, the driving of the motor can be controlled based on an external auxiliary controller, for example, a voice controller controls the motor, after the wearer wears a toy car, the arm supporting plate 25 is fixed on the arm, then the motor is reset, and the execution of the specification can be set, for example, the lifting or the falling, so that the control of the motor is realized; or the driving of the motor is controlled by adopting remote control; finally, high cooperativity between the exoskeleton and the human body and large strength assistance to the arms are realized; under the condition that the power supply energy is sufficient, continuous transportation can be realized. The size can be adjusted within a certain range to meet the requirements of workers with different body types.

Claims (10)

1. A human body wearing upper limb exoskeleton device for heavy load transportation is characterized by comprising a shoulder back plate device, a width adjusting device, a shoulder joint device and an arm driving device;

the shoulder backboard device comprises a shoulder pasting plate (1), a shoulder backboard rotating joint (3) and a shoulder rotating joint (4) are fixed on the shoulder pasting plate (1), two groups of width adjusting devices are symmetrically arranged on the shoulder pasting plate (1), and each group of width adjusting devices is connected with one group of shoulder joint device and an arm driving device;

the width adjusting device comprises a back width adjusting mechanism and a shoulder width adjusting mechanism, the back width adjusting mechanism comprises a waist-shoulder cross rod (7), and one end of the waist-shoulder cross rod (7) is rotatably connected with the shoulder-back plate rotating joint (3); the shoulder backboard rotating joint (3) comprises a shoulder cross rod (10), and one end of the shoulder cross rod (10) is rotatably connected with the other end of the waist and shoulder cross rod (7);

the shoulder joint device comprises a universal joint motor connecting rod (12), one end of the universal joint motor connecting rod (12) is connected with the other end of the shoulder cross rod (10) through a cross universal joint (11);

the arm driving device comprises a motor (21), the motor (21) is fixed at the other end of the universal joint motor connecting rod (12) through a motor mounting plate (13), an arm supporting plate (25) is fixed on an output shaft of the motor (21), and binding bands are arranged on the arm supporting plate (25) and the shoulder pasting plate (1).

2. The human body worn upper extremity exoskeleton device for heavy duty transport of claim 1, further comprising a height adjustment device comprising a waist support bar (18) and a waist positioning bar (17); one end of the waist support rod piece (18) is sleeved with one end of the waist positioning rod piece (17), the other end of the waist support rod piece (18) is fixed with a waist patch (20), and the waist patch (20) is provided with a fixing belt; a waist rotary joint (16) is fixed on the shoulder back plate (2), and the other end of the waist positioning rod piece (17) is rotationally connected with the waist rotary joint (16).

3. The human body-worn upper limb exoskeleton device for heavy load carrying according to claim 1, wherein the shoulder backboard rotating joint (3) and the shoulder backboard rotating joint (4) are both fixed at the lower end of the shoulder patch (1) through the shoulder backboard (2), the waist and shoulder rotating joint (15) is fixed on the shoulder backboard (2), and the upper end of the shoulder patch (1) is connected with the waist and shoulder rotating joint (15) through a waist and shoulder connecting shaft (14).

4. The human body wearing upper limb exoskeleton device for heavy load carrying as claimed in claim 1, wherein one end of the waist and shoulder cross bar (7) is rotatably connected with the shoulder and back plate rotating joint (3) through a back adjusting connecting rod (5), the back adjusting connecting rod (5) is vertically arranged, and the waist and shoulder cross bar (7) is horizontally arranged.

5. The human body worn upper extremity exoskeleton device for heavy duty transport of claim 1, wherein one end of the shoulder crossbar (10) is rotatably connected to the shoulder wide revolute joint (8) through a shoulder adjustment link (9).

6. The human body worn upper extremity exoskeleton device for heavy duty transport of claim 1, wherein the arm support plate (25) is fixedly connected with the output shaft of the motor (21) through the motor driven execution plate (23).

7. The human body worn upper extremity exoskeleton device for heavy duty transport of claim 6, wherein a three-dimensional force sensor (24) is provided between the arm support plate (25) and the motor-driven execution plate (23).

8. The human body wearing upper limb exoskeleton device for heavy load carrying as claimed in claim 7, wherein a motor motion limiting groove (22) is provided on the motor mounting plate (13), a limiting block is provided on the motor driving execution plate (23), and the limiting block on the motor driving execution plate (23) is limited by the motor motion limiting groove (22).

9. The human body worn upper extremity exoskeleton device for heavy duty transport of claim 1, wherein the shoulder backboard (2), the shoulder patch board (1) and the waist patch (20) are all arc-shaped structures.

10. The human body wearing upper limbs exoskeleton device for heavy load carrying as claimed in claim 1, wherein the shoulder back plate rotating joint (3), the shoulder rotating joint (4) and the shoulder width rotating joint (8) can all adopt bearing structures.

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