CN115520660A

CN115520660A - Pile up neatly machine people tongs with accurate positioning mechanism

Info

Publication number: CN115520660A
Application number: CN202211222937.4A
Authority: CN
Inventors: 刘德友
Original assignee: Guangzhou Topt Light Industry Machinery Co ltd
Current assignee: Guangzhou Topt Light Industry Machinery Co ltd
Priority date: 2022-10-08
Filing date: 2022-10-08
Publication date: 2022-12-27
Anticipated expiration: 2042-10-08
Also published as: CN115520660B

Abstract

The invention provides a robot palletizer gripper with an accurate positioning mechanism, and particularly relates to the technical field of robots. The method comprises the following steps: the tongs module, it includes: the fixed seat is provided with a movable cavity; the movable seat is movably connected with the fixed seat, the fixed seat is positioned at one side of the movable cavity, and the movable seat is fixedly connected with a positioning block; the gripper mechanism is positioned on the movable seat and is used for connecting the storage tray; the adjusting mechanism is positioned between the fixed seat and the movable seat and positioned in the movable cavity. The adjustment mechanism includes: the mounting block is fixedly connected to the movable seat; and one end of the telescopic rod is hinged with the mounting block, and the other end of the telescopic rod is hinged with the fixing seat. Still be connected with fixed subassembly between fixing base and installation piece, fixed subassembly is used for fixing between installation piece and the fixing base. The robot palletizer can effectively solve the problems that the conventional robot palletizer gripper is easy to generate collision and the gripping precision is low.

Description

Pile up neatly machine people tongs with accurate positioning mechanism

Technical Field

The invention relates to the technical field of robots, in particular to a robot palletizer gripper with an accurate positioning mechanism.

Background

The stacker crane usually picks and positions the goods by a gripper of a robot, and then stacks the goods into a material rack in sequence and stacks the goods.

It is common for a material rack to include a plurality of compartments with trays disposed within the compartments. Goods are usually placed on pallets, and robots grip the pallets to extract the material. Wherein, different compartments on the material frame correspond to respective coordinate numerical value. Thus, the robot may allow the pallet to be gripped by its gripper according to the corresponding coordinate information.

However, the precision of the robot is gradually reduced during long-term use, which causes the collision between the gripper of the robot and the pallet during use.

Disclosure of Invention

In view of the above disadvantages of the prior art, an object of the present invention is to provide a robot palletizer gripper with a precise positioning mechanism, so as to solve the problems that the existing robot palletizer gripper is easy to generate a collision and has low gripping precision.

To achieve the above and other related objects, the present invention provides a robot palletizer gripper with a precise positioning mechanism, comprising:

the tongs module is connected on pile up neatly machine people, the tongs module includes:

a fixed seat which is provided with a movable cavity;

the movable seat is movably connected with the fixed seat, the fixed seat is positioned on one side of the movable cavity, and a positioning block is fixedly connected to the movable seat;

the gripper mechanism is positioned on the movable seat and is used for connecting a storage tray; and

the adjusting mechanism is positioned between the fixed seat and the movable seat, and the adjusting mechanism is positioned in the movable cavity, wherein the adjusting mechanism comprises:

the mounting block is fixedly connected to the movable seat; and

one end of each telescopic rod is hinged with the corresponding mounting block, and the other end of each telescopic rod is hinged with the corresponding fixing seat;

the fixing seat and the mounting block are connected with a fixing component, and the fixing component is used for fixing the mounting block and the fixing seat.

In an aspect of the present invention, the gripper mechanism includes:

the fixing block is used for being clamped with a limiting hole arranged on the storage tray;

the driving wheel is positioned at one end of the fixed block, and the driving wheel is rotationally connected with the fixed block;

the driving block is positioned on the movable seat, wherein one end of the driving block is of an inclined surface structure, and the inclined surface structure is in contact with the driving wheel; and

the cylinder body of the cylinder is fixedly connected to the movable seat, and the cylinder rod of the cylinder is fixedly connected to the driving block;

the movable seat is provided with a cavity, and the driving wheel, the driving block and the fixed block are located in the cavity.

In one scheme of the invention, the movable seat further comprises a return spring, the return spring is positioned between the fixed block and the movable seat, and the return spring enables the fixed block to have a movement trend of retracting into the cavity.

In one aspect of the present invention, the four sets of telescopic rods are arranged in a central symmetry manner along the center of the mounting block.

In one scheme of the invention, the telescopic rod comprises a sliding sleeve and a sliding rod, wherein the sliding sleeve is connected with the sliding rod in a sliding manner, and a spring is connected between the sliding rod and the sliding sleeve.

In one scheme of the invention, spherical hinges are arranged between the telescopic rod and the fixed seat and between the telescopic rod and the mounting block.

In one aspect of the present invention, the fixing assembly includes a plurality of electromagnets, and the electromagnets are disposed on the fixing base. When the electromagnet is electrified, the electromagnet adsorbs the mounting block.

In one aspect of the present invention, a gap exists between the mounting block and the bottom surface of the fixing base.

In one aspect of the present invention, an end of the positioning block is a hemisphere.

In summary, the invention discloses a robot palletizer gripper with a precise positioning mechanism, which can realize precise positioning of a gripping position within a certain precision range by clamping a positioning block and a positioning hole.

The hemispherical positioning block can move along the empty surface of the positioning hole, so that the gripper module enters an accurate gripping position. Through the positioning action between locating piece and the locating hole for the robot need not too high positioning accuracy to and in the contact range of locating piece and locating hole, all can realize snatching the storage charging tray.

Meanwhile, a certain included angle is formed between the telescopic rod and the bottom surface of the movable cavity, so that the telescopic rod and the bottom surface of the movable cavity are in a triangular structure. Therefore, the stability of the mounting block and the fixing seat in the connection process can be improved, and the grabbing precision of the grabbing mechanism in the grabbing process of the storage material disc is further improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic structural view of a palletizing robot gripper with a precise positioning mechanism according to an embodiment of the present invention;

fig. 2 is a schematic view of a gripper module of a palletizing robot gripper with a precise positioning mechanism according to an embodiment of the present invention;

fig. 3 is a schematic structural view of a second moving module of the palletizing robot gripper with a precise positioning mechanism in an embodiment of the invention;

FIG. 4 is a schematic diagram of a storage module of a palletizing robot gripper with a precise positioning mechanism according to an embodiment of the present invention;

FIG. 5 is an enlarged view of view A of FIG. 4;

FIG. 6 is a schematic diagram of an adjustment mechanism of the robot palletizer gripper with a precise positioning mechanism according to an embodiment of the present invention;

fig. 7 is a schematic structural view of a telescopic rod of the robot palletizer gripper with a precise positioning mechanism in an embodiment of the invention;

fig. 8 is a schematic partly in section of a gripper module of a palletizing robot gripper with a precision positioning mechanism according to an embodiment of the present invention;

fig. 9 is a schematic structural view of a fixing assembly of the robot palletizer gripper with the precise positioning mechanism in an embodiment of the invention.

Description of the element reference numerals

100. A base plate;

110. a storage module; 111. a storage compartment; 112. a partition plate; 113. storing the material tray; 114. a limiting hole; 115. positioning holes;

120. a first moving module; 121. a mounting base; 122. a guide bar; 123. a lifting motor; 124. a lifting screw rod; 125. mounting a plate; 126. a fixing plate;

130. a second moving module; 131. transversely moving the screw rod; 132. a slider; 133. a traversing motor; 134. limiting a guide rail;

200. a gripper module;

210. a telescopic cylinder;

220. a fixed seat; 221. a telescopic rod; 222. mounting blocks; 2210. a sliding sleeve; 2211. a slide bar; 223. an electromagnet; 224. a movable cavity;

230. a movable seat; 231. positioning blocks; 232. a fixed block; 233. a cylinder; 234. a drive block; 235. a drive wheel; 236. a return spring; 237. a cavity.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

Please refer to fig. 1 to 9. It should be understood that the structures, ratios, sizes, and the like shown in the drawings are only used for matching the disclosure of the present disclosure, and are not used for limiting the conditions of the present disclosure, so that the present disclosure is not limited to the technical essence, and any modifications of the structures, changes of the ratios, or adjustments of the sizes, can still fall within the scope of the present disclosure without affecting the function and the achievable purpose of the present disclosure.

Referring to fig. 1, the present invention provides a robot palletizer gripper with a precise positioning mechanism, which can be used to solve the problems that the existing robot palletizer gripper is easy to generate a collision and has low gripping precision. The robot palletizer gripper with accurate positioning function can comprise a gripper module 200, and the gripper module 200 is connected to the robot palletizer. Therefore, the robot palletizer drives the gripper module 200 to adjust the position, and the gripper module 200 grips the material. It should be noted that a positioning assembly is also attached to the gripper module 200. Therefore, it is possible to allow the gripper module 200 to maintain good gripping accuracy during the gripping of the storage tray 113 by the positioning member.

Referring to fig. 1 and 3, in an embodiment, the palletizing robot may include a multi-degree-of-freedom mechanical arm, such as a six-degree-of-freedom or four-degree-of-freedom mechanical arm, or may allow a bi-directional moving platform to be used, which is not limited thereto. In the present embodiment, the palletizing robot is taken as an example of a bidirectional moving platform for explanation and explanation.

In particular, in an embodiment, the palletizing robot may include a first moving module 120 and a second moving module 130, and the gripper module 200 may be coupled to the first moving module 120. Thus, movement of the gripper module 200 in one direction is achieved by the first movement module 120 and movement of the gripper module 200 in the other direction is achieved by the second movement module 130. The moving directions of the first moving module 120 and the second moving module 130 may be allowed to be perpendicular to each other.

Referring to fig. 1, in one embodiment, the first transportation module may include a mounting base 121, a guide rod 122, a lifting motor 123, a lifting screw 124, a mounting plate 125, and a fixing plate 126. The mounting seat 121 and the fixing plate 126 are parallel to each other, and the guide rod 122 is located between the mounting seat 121 and the fixing plate 126. The guide rods 122 may be provided in multiple sets, and the multiple sets of guide rods 122 are parallel to each other. One end of the guide rod 122 is fixedly connected with the mounting seat 121, and the other end of the guide rod 122 is fixedly connected with the fixing plate 126. The axis of the lifting screw 124 is parallel to the axis of the guide rod 122, and the lifting screw 124 is located between the mounting seat 121 and the fixing plate 126. One end of the lifting screw 124 is rotatably connected to the mounting base 121, the other end of the lifting screw 124 is rotatably connected to the fixing plate 126, and the lifting motor 123 is in transmission connection with the lifting screw 124. Therefore, the elevation screw 124 can be driven to rotate by the elevation motor 123.

Referring to fig. 2, in one embodiment, the mounting plate 125 is slidably connected to the guide rod 122, and the mounting plate 125 is in transmission connection with the lifting screw 124. Therefore, the mounting plate 125 can be driven to move in the axial direction of the elevation screw 124 by the rotation of the elevation screw 124. Meanwhile, a telescopic cylinder 210 is connected to the mounting plate 125, and the gripper module 200 is connected to the telescopic cylinder 210, so that the gripper module 200 is driven by the telescopic cylinder 210 to move along the axial direction of the telescopic cylinder 210.

Referring to fig. 3, in one embodiment, the second transportation module may include a traverse screw 131, a slider 132, a traverse motor 133, and a limit rail 134. The traverse screw 131 is located on the bottom plate 100, the slider 132 is in transmission connection with the screw, and the slider 132 is in fixed connection with the mounting seat 121. The position limiting rail 134 is located between the base plate 100 and the mounting seat 121, so that the stability of the mounting seat 121 relative to the base plate 100 during sliding is improved by the position limiting rail 134. The traverse motor 133 is fixedly connected to the base plate 100, and the traverse motor 133 is in transmission connection with the traverse screw 131. Accordingly, the traverse screw 131 is driven to rotate by the traverse motor 133, and the mount 121 is driven to move in the circumferential direction of the traverse screw 131 by the rotation of the traverse screw 131.

Referring to fig. 1, 4 and 5, in one embodiment, the palletizing robot is connected to a base plate 100, and a side of the base plate 100 allows a storage module 110 to be connected. Wherein the storage tray 113 is located in the storage module 110, so the storage tray 113 is transported to the storage module 110 by the palletizing robot. Specifically, the storage module 110 may be constructed by a plurality of partitions 112 parallel to each other, and storage compartments 111 are opened between adjacent partitions 112. Wherein, the storage tray 113 is located in the compartment, and the material is located in the storage tray 113. Therefore, the gripper module 200 allows for the material to be palletized and picked by the storage tray 113.

Referring to fig. 2-8, in one embodiment, the gripper module 200 may include a fixed base 220, a movable base 230, a gripper mechanism, and an adjustment mechanism. Wherein, the fixing base 220 can be allowed to be provided with a movable cavity 224, and the adjusting structure is positioned in the movable cavity 224. Specifically, the movable seat 230 is fixedly connected to the fixed seat 220, the movable seat 230 is located at one side of the movable cavity 224, and the fixed seat 220 and the movable seat 230 are connected through an adjusting mechanism. Specifically, the adjusting structure may include a mounting block 222 and a plurality of telescopic rods 221, the mounting block 222 is fixedly connected to the movable base 230, and the telescopic rods 221 are connected between the mounting block 222 and the fixed base 220. Wherein, one end of the telescopic rod 221 is hinged to the mounting block 222, and the other end of the telescopic rod 221 is hinged to the fixing base 220. Therefore, the installation block 222 can allow multi-directional movement in the movable cavity 224 by the extension rod 221 disposed at the periphery of the installation block 222. For the extension rod 221, an elastic structure may be allowed. By setting the telescopic rod 221 to be an elastic structure, the telescopic rod 221 can be timely restored to the initial state without the action of external force.

Specifically, the telescopic rods 221 may be provided in four sets, and the four sets of telescopic rods 221 are disposed in central symmetry along the central position of the mounting block 222. In one embodiment, the extension rod 221 may include a sliding sleeve 2210 and a sliding rod 2211, and the sliding sleeve 2210 and the sliding rod 2211 are slidably connected. It should be noted that a spring may be provided between the sliding sleeve 2210 and the sliding rod 2211, so that the mounting block 222 can be adjusted in the movable cavity 224 by providing a resilient structure between the sliding rod 2211 and the sliding sleeve 2210. Since the movable stage 230 is connected to the mounting stage 121, a synchronous movement between the movable stage 230 and the mounting stage 121 is allowed. It should be noted that the telescopic rod 221 and the fixing base 220, and the telescopic rod 221 and the mounting block 222 are connected by a spherical hinge. Meanwhile, a certain gap exists between the mounting block 222 and the bottom surface of the movable cavity 224.

The movable base 230 is further connected to a positioning block 231, and a positioning hole 115 is formed in the partition plate 112 of the storage module 110. The positioning hole 115 is adapted to the end structure of the positioning block 231, and the end of the positioning block 231 is hemispherical. Therefore, when the gripper module 200 is gripping the storage tray 113, the positioning block 231 may be first engaged with the positioning hole 115. The positioning block 231 is located on the movable seat 230, and the movable seat 230 is movably connected with the fixed seat 220. Accordingly, it is possible to allow the gripper module 200 to be positioned by the positioning block 231 within a certain accuracy range. The hemispherical positioning block 231 may be moved along the empty surface of the positioning hole 115 so that the gripper module 200 enters a precise gripping position. Meanwhile, through the positioning function between the positioning block 231 and the positioning hole 115, the robot can grasp the storage tray 113 without high positioning accuracy and within the contact range of the positioning block 231 and the positioning hole 115.

Referring to fig. 8, in one embodiment, the gripping mechanism is located on the movable base 230 and is used for gripping the material storage tray 113. Specifically, the gripper mechanism may include a fixing block 232, a driving wheel 235, a driving block 234, and an air cylinder 233, wherein at least one set of the fixing block 232 is provided. In one embodiment, two sets of fixing blocks 232 are disposed, and two sets of limiting holes 114 are correspondingly disposed on the storage tray 113. Therefore, the fixing block 232 is clamped with the limiting hole 114 on the storage tray 113 to realize the grabbing of the storage tray 113.

Specifically, a cavity 237 may be allowed to be formed on the movable seat 230, and the driving wheel 235, the driving block 234 and the fixed block 232 may be allowed to be located in the cavity 237. Wherein, the cylinder 233 is fixedly connected to the movable base 230, and the cylinder 233 is used for driving the driving block 234 to move in a specific direction. The end of drive block 234 may allow for a ramp configuration to be used and the ramp configuration acts on drive wheel 235. The drive wheel 235 is rotatably coupled to the fixed block 232 and the ramp structure on the drive block 234 allows for the drive wheel 235 to be acted upon to further drive the fixed block 232 into motion as the drive block 234 is moved. It should be noted that a return spring 236 is further connected between the driving block 234 and the movable seat 230, and the return spring 236 is used for providing the fixed block 232 with a movement tendency into the cavity 237. Thus, when the drive block 234 and the drive wheel 235 are free from restraint, the return spring 236 can urge the fixed block 232 into the cavity 237.

Therefore, in the actual working process of the gripper mechanism, the gripper mechanism is first positioned by the clamping between the positioning block 231 and the positioning hole 115, and at this time, the fixing block 232 is located in the cavity 237. After the clamping between the positioning block 231 and the positioning hole 115 is completed, the driving block 234 may be driven to move by the air cylinder 233, and the positioning block 231 drives the fixing block 232 to clamp the limiting hole 114 by the driving wheel 235 in the moving process, so as to grasp the storage tray 113.

Referring to fig. 9, in an embodiment, a fixing component may be allowed to be connected between the fixing base 220 and the mounting block 222, and the fixing component is used for achieving a relative fixing state between the fixing base 220 and the mounting block 222. Therefore, when the gripping mechanism is in a clamping state with the storage tray 113, it is necessary to ensure that the movable seat 230 and the fixed seat 220 are in a relatively fixed state, so as to avoid the shaking phenomenon occurring during the process of storing or taking the storage tray 113 by the robot. Specifically, the fixing assembly may include a plurality of electromagnets 223, and the electromagnets 223 are located inside the fixing base 220. The mounting block 222 is made of a magnetic material, so that when the electromagnet 223 obtains a trigger instruction, the electromagnet 223 absorbs the mounting block 222, and the mounting block 222 is tightly connected to the bottom surface of the movable cavity 224.

It should be noted that when the mounting block 222 is tightly connected to the bottom surface of the movable cavity 224, there is an angle between the plurality of telescopic rods 221 located on the mounting block 222. Therefore, the attraction between the electromagnet 223 and the mounting block 222 can ensure that the mounting block 222 and the fixing seat 220 are in a relatively fixed state. Meanwhile, a certain included angle exists between the bottom surfaces of the telescopic rod 221 and the movable cavity 224, so that the bottom surfaces of the telescopic rod 221 and the movable cavity 224 are in a triangular structure. Therefore, the stability of the connection between the mounting block 222 and the fixing base 220 during the connection process can be improved, so as to improve the gripping accuracy of the gripping mechanism during the gripping of the storage tray 113.

In summary, the present invention discloses a robot palletizer gripper with a precise positioning mechanism, which is capable of precisely positioning a gripping position within a certain precision range by engaging a positioning block 231 with a positioning hole 115. The hemispherical positioning block 231 may be moved along the empty surface of the positioning hole 115 so that the gripper module 200 enters a precise gripping position. Meanwhile, due to the positioning function between the positioning block 231 and the positioning hole 115, the robot can grasp the storage tray 113 without high positioning accuracy and within the contact range of the positioning block 231 and the positioning hole 115.

Meanwhile, a certain included angle exists between the bottom surfaces of the telescopic rod 221 and the movable cavity 224, so that the bottom surfaces of the telescopic rod 221 and the movable cavity 224 are in a triangular structure. Therefore, the stability of the connection between the mounting block 222 and the fixing seat 220 during the connection process can be improved, and the gripping accuracy of the gripping mechanism during the gripping of the storage tray 113 can be further improved.

Therefore, the invention effectively overcomes some practical problems in the prior art, thereby having high utilization value and use significance.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Also, when numerical ranges are given in the examples, it is understood that both endpoints of each of the numerical ranges and any value therebetween can be selected unless the invention otherwise indicated. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs and the description of the present invention, and any methods, apparatuses, and materials similar or equivalent to those described in the examples of the present invention may be used to practice the present invention.

Claims

1. The utility model provides a pile up neatly machine people tongs with accurate positioning mechanism which characterized in that includes:

a gripper module (200) connected to the palletizing robot, the gripper module (200) comprising:

a fixed seat (220) which is provided with a movable cavity (224);

the movable seat (230) is movably connected with the fixed seat (220), the fixed seat (220) is positioned on one side of the movable cavity (224), and a positioning block (231) is fixedly connected to the movable seat (230);

the gripping mechanism is positioned on the movable seat (230) and is used for connecting the storage tray (113); and the number of the first and second groups,

an adjustment mechanism located between the fixed seat (220) and the movable seat (230), the adjustment mechanism being located within the movable chamber (224), wherein the adjustment mechanism comprises:

a mounting block (222) fixedly connected to the movable base (230); and the number of the first and second groups,

a plurality of telescopic rods (221), wherein one end of each telescopic rod (221) is hinged with the corresponding mounting block (222), and the other end of each telescopic rod (221) is hinged with the corresponding fixing seat (220);

and a fixing component is further connected between the fixing seat (220) and the mounting block (222), and the fixing component is used for realizing the relative fixation between the mounting block (222) and the fixing seat (220).

2. Palletizing robot gripper according to claim 1, characterized in that it comprises:

the fixing block (232) is used for being clamped with a limiting hole (114) arranged on the storage tray (113);

the driving wheel (235) is positioned at one end of the fixed block (232), and the driving wheel (235) is rotatably connected with the fixed block (232);

the driving block (234) is positioned on the movable seat (230), wherein one end of the driving block (234) is of a slope structure, and the slope structure is in contact with the driving wheel (235); and

the cylinder body of the cylinder (233) is fixedly connected to the movable seat (230), and the cylinder rod of the cylinder (233) is fixedly connected to the driving block (234);

a cavity (237) is arranged on the movable seat (230), and the driving wheel (235), the driving block (234) and the fixed block (232) are located in the cavity (237).

3. The palletizing robot gripper with a precise positioning mechanism according to claim 2, characterized in that it further comprises a return spring (236), the return spring (236) being located between the fixed block (232) and the movable seat (230), and the return spring (236) providing the fixed block (232) with a tendency to move back inside the cavity (237).

4. The palletizing robot gripper with a precise positioning mechanism according to claim 1, characterized in that the telescopic rods (221) comprise four groups, and the four groups of telescopic rods (221) are arranged in a central symmetry along the center of the mounting block (222).

5. Palletizing robot gripper with a precision positioning mechanism according to claim 4, characterized in that said telescopic rod (221) comprises a sliding sleeve (2210) and a sliding rod (2211);

wherein, sliding connection between sliding sleeve (2210) and slide bar (2211), and be connected with the spring between slide bar (2211) and sliding sleeve (2210).

6. Palletizing robot gripper with a precise positioning mechanism according to claim 5, characterized in that the telescopic rod (221) is ball-hinged to the fixed seat (220) and the telescopic rod (221) is ball-hinged to the mounting block (222).

7. The palletizing robot gripper with a precision positioning mechanism as claimed in claim 1, characterized in that the fixing assembly comprises a plurality of electromagnets (223), the electromagnets (223) being arranged on the fixing seat (220);

wherein when the electromagnet (223) is energized, the electromagnet (223) attracts the mounting block (222).

8. The palletizing robot gripper with a precise positioning mechanism according to claim 7, characterized in that a gap exists between the mounting block (222) and the bottom surface of the fixed seat (220).

9. Palletizing robot gripper with a precise positioning mechanism according to claim 1, characterized in that the end of the positioning block (231) is hemispherical.