Method and controller for controlling a gripping apparatus

Abstract

A method of controlling a gripping apparatus comprises determining that the force acting on one or more closing jaws of the gripping apparatus has increased at a first jaw spacing, causing the grippin

Description

TECHNOLOGICAL FIELD Examples of the disclosure relate to a method and controller for controlling a gripping apparatus. Some relate to a method and controller for controlling a gripping apparatus to grip rigid objects safely. BACKGROUND Gripping apparatuses are often mounted to robotic arms, and can be used in a wide variety of industries. For example, a gripping apparatus mounted to a robotic arm can be used to pick up a component or product on an assembly line, assemble parts, manipulate tools, sort products, pick fruits or vegetables, prune plants, or carry out medical surgery. In some cases, it is desirable to measure the gripping force applied by a gripping apparatus, to improve the efficiency and safety of the operation of the gripping apparatus. Often, however, the measurement of the gripping force is inaccurate, unidirectional, and / or imposes limits on the configuration of the gripping apparatus. Furthermore, there is a desire to reduce the risk of the gripping apparatus applying high forces to an operator of the gripping apparatus or items that are not intended to be gripped, to improve safety and reduce accidental damage. BRIEF SUMMARY According to various, but not necessarily all, examples there is provided a gripping apparatus for gripping an object, the apparatus comprising: a jaw, wherein the jaw comprises a first part and a second part, the second part being configured to grip an object; an actuator configured to urge the first part of the jaw; an elastic component, wherein the elastic component is locatable between the first part of the jaw and the second part of the jaw, such that force can be transmitted between the first part of the jaw and the second part of the jaw via the elastic component; and a sensor configured to measure the relative displacement of the first part of the jaw and the second part of the jaw. The actuator may be configured to urge the first part of the jaw substantially parallel to a first axis. The sensor may be configured to measure the relative displacement of the first part of the jaw and the second part of the jaw substantially parallel to the first axis. The sensor may be an optical sensor. The sensor may be a slotted optical switch. The sensor may comprise: a slotted structure, the slotted structure comprising a slot and a light source configured to emit light along a path across the slot, the slotted structure further comprising a light detector configured to detect the intensity of light passing along the path; and a shutter, the shutter being movable substantially parallel to the first axis through the slot, wherein the slotted structure is mounted to one of the first or second part of the jaw, and the shutter is mounted to the other of the first or second part of the jaw. The gripping apparatus may comprise a further sensor configured to measure the relative displacement of the first part of the jaw and the second part of the jaw. The further sensor may be configured to measure the relative displacement of the first part of the jaw and the second part of the jaw substantially parallel to the first axis. The further sensor may comprise: a slotted structure, the slotted structure comprising a slot and a light source configured to emit light along a path across the slot, the slotted structure further comprising a light detector configured to detect the intensity of light passing along the path; and a shutter, the shutter being movable substantially parallel to the first axis through the slot, wherein the slotted structure is mounted to one of the first or second part of the jaw, and the shutter is mounted to the other of the first or second part of the jaw. The sensor and further sensor may be configured such that movement of the first part of the jaw relative to the second part of the jaw in a first direction substantially parallel to the first axis causes the shutter of the sensor to move to permit more light along the path across the slot of the sensor, and causes the shutter of the further sensor to move to permit less light along the path across the slot of the further sensor. The elastic component may be in the form of an elastic pad. The elastic component may comprise an elastomeric material. The elastic component may comprise at least one of the following: polyurethane, acrylic, or silicone. The first or second part of the jaw may comprise a projection and the other of the first or second part may include a recess for locating the projection. The projection may project substantially perpendicularly to the first axis. The elastic component may be located in the recess. The first part may be coupled to the second part by one or more jaw rails. The actuator may be an electric motor. The actuator may be a stepper motor. The actuator may comprise a wedge configured to urge the first part substantially parallel to the first axis. The gripping apparatus may further comprise an actuation rail, the actuation rail extending substantially parallel to the first axis, and wherein the first part of the jaw is mounted to and movable along the actuation rail. The gripping apparatus may comprise a further jaw which opposes the jaw. The further jaw may include the same features as the jaw. The gripping apparatus may further comprise a controller configured to determine the gripping force applied by the gripping apparatus based at least in part on the sensed relative displacement. According to various, but not necessarily all, examples there is provided a gripping system, wherein the system comprises: a robotic arm; and the gripping apparatus of any of the preceding paragraphs, the gripping apparatus being mounted to the robotic arm. According to various, but not necessarily all, examples there is provided a method of controlling a gripping apparatus, the method comprising: determining that the force acting on one or more closing jaws of the gripping apparatus has increased at a first jaw spacing; and causing the gripping apparatus to operate in a first mode of operation when the jaw spacing is between the first jaw spacing and a threshold jaw spacing and operate in a second mode of operation when the jaw spacing is at or beyond the threshold jaw spacing, wherein in the first mode of operation the gripping apparatus is configured such that the one or more jaws apply gripping force up to a first amount of gripping force and in the second mode of operation the gripping apparatus is configured such that the one or more jaws apply gripping force up to a second amount of gripping force, wherein the first amount of gripping force is greater than the second amount of gripping force. The method may further comprise determining that the first jaw spacing is between the threshold jaw spacing and a further threshold jaw spacing. The causing the gripping apparatus to operate in a first mode of operation when the jaw spacing is between the first jaw spacing and the threshold jaw spacing and operate in a second mode of operation when the jaw spacing is at or beyond the threshold jaw spacing may comprise: causing the gripping apparatus to operate in the first mode of operation when the jaw spacing is between the threshold jaw spacing and the further threshold jaw spacing and operate in the second mode of operation when the jaw spacing is not between the threshold jaw spacing and the further threshold jaw spacing, based at least in part on the determination that the force acting on one or more closing jaws of the gripping apparatus has increased at the first jaw spacing and the determination that the first jaw spacing is between the threshold jaw spacing and the further threshold jaw spacing. The determining that the force acting on one or more closing jaws of the gripping apparatus has increased at a first jaw spacing may comprise: receiving a signal comprising first information, wherein the first information is indicative of the force acting on one or more closing jaws at a first time during the closure of the one or more jaws; receiving a signal comprising second information, wherein the second information is indicative of the force acting on the one or more closing jaws at a second time during the closure of the jaws, the second time being later than the first time; and determining that the force at the second time is greater than the force at the first time, and wherein the first jaw spacing is the jaw spacing at the second time. The threshold jaw spacing may be predetermined. The further threshold jaw spacing may be predetermined. The method may further comprise, prior to causing the gripping apparatus to operate in the first mode of operation when the jaw spacing is between the first jaw spacing and the threshold jaw spacing and operate in a second mode of operation when the jaw spacing is at or beyond the threshold jaw spacing: determining the threshold jaw spacing as a predetermined distance from the first jaw spacing. The method further may further comprise: causing the one or more jaws to open; determining that the force acting on one or more opening jaws of the gripping apparatus has increased; and reducing the force being applied by the one or more jaws of the gripping apparatus substantially immediately, based at least in part on the determination that the force acting on one or more opening jaws of the gripping apparatus has increased. The determining that the force acting on one or more opening jaws of the gripping apparatus has increased may comprise: receiving a signal comprising third information, wherein the third information is indicative of the force acting on the one or more opening jaws at a third time during the opening of the jaws; receiving a signal comprising fourth information, wherein the fourth information is indicative of the force acting on the one or more opening jaws at a fourth time during the opening of the jaws, the fourth time being later than the third time; and determining that the force at the fourth time is greater than the force at the third time. According to various, but not necessarily all, examples there is provided a method of controlling a gripping apparatus, the method comprising: determining that the rate of change of force acting on one or more closing jaws of the gripping apparatus is above a first threshold rate of change of force and is below a second threshold rate of change of force; reducing the gripping force being applied by the one or more jaws of the gripping apparatus substantially immediately, based at least in part on the determination that the rate of change of force acting on one or more closing jaws of the gripping apparatus is above the first threshold rate of change of force and is below the second threshold rate of change of force. According to various, but not necessarily all, examples there is provided a controller comprising means for carrying out the method of any of the preceding paragraphs. According to various, but not necessarily all, examples there is provided a gripping apparatus for gripping an object, the apparatus comprising: one or more jaws; an actuator configured to urge the one or more jaws to open or close the one or more jaws; a sensor configured to provide information indicative of the force acting on the one or more jaws; and the controller of the preceding paragraph. According to various, but not necessarily all, examples there is provided a gripping system, wherein the system comprises: a robotic arm; and the gripping apparatus of the preceding paragraph, the gripping apparatus being mounted to the robotic arm. According to various, but not necessarily all, examples there is provided a computer program comprising program instructions for causing an apparatus to perform the method of any of the preceding paragraphs. According to various, but not necessarily all, examples there is provided a controller comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the controller at least to perform the method of any of the preceding paragraphs. According to various, but not necessarily all, embodiments there is provided an apparatus comprising means for performing at least part of one or more methods described herein. The description of a function and / or action should additionally be considered to also disclose any means suitable for performing that function and / or action. Functions and / or actions described herein can be performed in any suitable way using any suitable method. According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims. While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. The description of a function should additionally be considered to also disclose any means suitable for performing that function. BRIEF DESCRIPTION Some examples will now be described with reference to the accompanying drawings in which: Fig. 1 schematically shows a gripping apparatus; Fig. 2 schematically shows a gripping system; Fig. 3 schematically shows an example controller; Fig. 4 schematically shows communication between a sensor, a controller and an actuator; Fig. 5 shows a perspective view of an example gripping apparatus; Fig. 6 shows a front view of the example gripping apparatus of Fig. 5; Fig. 7 shows a front view of a jaw and an elastic component of the example gripping apparatus of Fig. 5; Fig. 8 shows a perspective view of a first part of the jaw of Fig. 7; Fig. 9 shows a perspective view of a second part of the jaw of Fig. 7; Fig. 10 shows a perspective view of the elastic component of Fig. 7; Fig. 11 shows a perspective view of a portion of the second part of the jaw, jaw rails, and a sensor of the example gripping apparatus of Fig. 5; Fig. 12 shows a perspective view of an actuator of the example gripping apparatus of Fig. 5; Fig. 13 shows a perspective view of the actuator, the first part of the jaw, the elastic component, a portion of the second part of the jaw, and actuator rails of the example gripping apparatus of Fig. 5; Fig. 14 shows a perspective view of the sensor of Fig. 11; Fig. 15 shows schematic cross-sectional view of a slotted structure of the sensor of Fig. 14; Fig. 16 shows a method of controlling a gripping apparatus; Fig. 17 shows an example method of controlling a gripping apparatus; Fig. 18 shows a further example method of controlling a gripping apparatus; Fig. 19 shows a front view of a threshold jaw spacing and a further threshold jaw spacing of the gripping apparatus of Fig. 5, along with a finger; Fig. 20 shows a further method of controlling a gripping apparatus; and Fig. 21 shows a yet further method of controlling a gripping apparatus. The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. DETAILED DESCRIPTION Embodiments of the disclosure relate to a gripping apparatus, a gripping system, a method of controlling a gripping apparatus, and a controller for the gripping apparatus. Fig. 1 shows a gripping apparatus 100. The gripping apparatus 100 comprises one or more jaws 110, an actuator 130 configured to urge the one or more jaws 110 to open or close the one or more jaws 110, and a sensor 140 configured to provide information indicative of the force acting on the one or more jaws 110. The one or more jaws 110 may comprise two jaws. The two jaws may be two opposing jaws. The gripping apparatus 100 could grip an object on an external surface of the object (e.g. the outer surface of a sphere or cube) by urging the one or more jaws 110 inwardly, or the gripping apparatus 100 may grip an object on an internal surface (e.g. the inner surface of a cup or bowl) of the object by urging the one or more jaws 110 outwardly. Figs. 5 and 6 show an example gripping apparatus 1000. The example gripping apparatus 1000 includes a jaw 1100, an elastic component 1200, an actuator 1300 and a sensor 1400. The actuator 1300 of the gripping apparatus 1000 is shown in Figs. 12 and 13, and the sensor 1400 of the gripping apparatus 1000 is shown in Figs. 11, 14 and 15. The jaw 1100 includes a first part 1110 and a second part 1120, as best shown in Figs. 7 to 9. The first part 1110 is movable relative to the second part 1120. In this example, the first part 1110 is movable relative to the second part 1120 substantially parallel to a first axis 50. The first axis 50 is shown in Figs. 5,6,7,11 and 13. The first part 1110 of the jaw 1100 could alternatively be referred to as a base 1110 of the jaw 1100, and the second part 1120 of the jaw 1100 could alternatively be referred to as a finger 1120 of the jaw 1100. The first and second parts 1110, 1120 may be made substantially from metal and / or a plastics material. The second part 1120 of the jaw 1100 is configured to grip an object. The second part 1120 of the jaw 1100 may be substantially L-shaped. In the example gripping apparatus 1000, the second part 1120 comprises a gripping surface 1122. The gripping surface 1122 may extend in a plane that is substantially perpendicular to the first axis 50. The gripping surface 1122 may comprise a plurality of serrations to aid with gripping. An example first part 1110 of the jaw 1100 is shown in Fig. 8. In this example, the first part 1110 of the jaw 1100 includes a projection 1112. The projection 1112 may project in a direction which is non-parallel to the first axis 50. The projection 1112 projects substantially perpendicularly to the first axis 50 in the example first part 1110, as shown in Fig. 7. The projection 1112 is for insertion into a recess 1124 in the second part 1120. The recess 1124 in the second part 1120 is shown in Fig. 9. The projection 1112 is configured for insertion in the recess 1124 such that movement of the first part 1110 relative to the second part 1120 causes force to be transmitted between the first part 1110 and the second part 1120. In particular in this example, movement of the first part 1110 relative to the second part 1120 in a dimension substantially parallel to the first axis causes force to be transmitted between the first part 1110 and the second part 1120. Additionally, or alternatively, the second part 1120 may include a projection (not shown in the example gripping apparatus 1000) for insertion into a corresponding recess (not shown in the example gripping apparatus 1000) in the first part 1110, which can interact in a similar manner to the projection 1112 and recess 1124 described above. The first part 1110 of the jaw 1100 thus includes an engagement surface 1118 configured to transmit force between the first part 1110 and the second part 1120 of the jaw 1100, which is labelled in Fig. 8. The engagement surface 1118 of the first part 1110 of the jaw 1100 is non-parallel to the first axis 50. In some examples, the engagement surface 1118 of the first part 1110 of the jaw 1100 extends in a plane substantially perpendicular to the first axis 50. The engagement surface 1118 of the first part 1110 of the jaw 1100 may be provided by a side wall of the projection 1112. The second part 1120 of the jaw 1100 also includes an engagement surface 1128 configured to transmit force between the first part 1110 and the second part 1120 of the jaw 1100, as shown in Fig. 9. The engagement surface 1128 of the second part 1120 of the jaw 1100 is non-parallel to the first axis 50. In some examples, the engagement surface 1128 of the second part 1120 of the jaw 1100 extends in a plane substantially perpendicular to the first axis 50. The engagement surface 1128 of the second part 1110 of the jaw 1100 may be provided by a side wall of the recess 1124. The engagement surface 1128 of the second part 1120 of the jaw 1100 may be substantially parallel to the engagement surface 1118 of the first part 1110 of the jaw 1100. In this example, the first part 1110 of the jaw 1000 further comprises a slot 1115 for engaging with the actuator 1300, as shown in Figs. 8 and 13. The slot 1115 is shaped to receive a wedge 1320 of the actuator 1300, which is described in further detail later in the description. The slot 1115 comprises a tapered surface for engaging with a tapered surface of the wedge 1320. The tapered surface of the slot 1115 may extend in a plane that is at an oblique angle relative to the first axis 50. As shown best in Fig. 13, the example gripping apparatus 1000 further comprises one or more actuation rails 1060, the one or more actuation rails 1060 may extend substantially parallel to the first axis 50 (i.e., the elongate dimension of the one or more actuation rails 1060 may be substantially parallel to the first axis 50). The first part 1110 of the jaw 1100 is mounted to the one or more actuation rails 1060, and is movable along the one or more actuation rails 1060. The first part 1110 of the jaw 1100 may be slidable along the one or more actuation rails 1060. The one or more actuation rails 1060 may be mounted to a housing 1050 of the example gripping apparatus 1000. The housing 1050 is not shown in Fig. 13 for clarity, but the housing is shown in Figs. 5 &6. In this example, the first part 1110 of the jaw 1000 further comprises one or more recessed channels 1117 for locating the one or more actuation rails 1060, as shown in Fig. 8. The elongate dimension of the one or more recessed channels 1117 may be substantially parallel to the first axis 50. In some examples, the jaw 1100 further comprises one or more jaw rails 1130, as shown best in Fig. 11. The first and second parts 1110, 1120 may be coupled to one another by the jaw rails 1130. The first and second parts 1110, 1120 may each be mounted to the one or more jaw rails 1130 to permit relative movement between the first part 1110 and second part 1120. In this example, the second part 1120 of the jaw 1100 is fixed in position relative to the one or more jaw rails 1130, and the first part 1110 is slidably movable along the one or more jaw rails 1130. In other examples, the first part 1110 of the jaw 1100 could be fixed in position relative to the one or more jaw rails 1130, and the second part 1120 could be slidably movable along the one or more jaw rails 1130. In the example gripping apparatus 1000 shown in Figs. 5 to 15, the jaw 1100 comprises two rails 1130. The one or more jaw rails 1130 may extend substantially parallel to the first axis 50 (i.e., the elongate dimension of the one or more jaw rails 1130 may be substantially parallel to the first axis 50). In this example, the first part 1110 of the jaw 1000 further comprises one or more holes 1119 for locating the one or more jaw rails 1130, as shown in Fig. 8. The one or more holes 1119 may extend in a dimension which is substantially parallel to the first axis 50. The second part 1120 of the jaw 1000 may further comprise one or more holes 1129 for locating the one or more jaw rails 1130, as shown in Fig. 9. The one or more holes 1129 may extend in a dimension which is substantially parallel to the first axis 50. As shown for instance in Figs. 5 to 7 and 11, the elastic component 1200 of the gripping apparatus 1000 is locatable between the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100 such that force can be transmitted between the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 100 via the elastic component 1200. The elastic component 1200 is configured to elastically deform. The second part 1120 of the jaw 1100 is configured to transfer force to the first part 1110 of the jaw 1100 via the elastic component 1200. The first part 1110 of the jaw 1100 may be mechanically coupled to the second part 1120 of the jaw 1100 via the elastic component 1200. In some examples, the elastic component 1200 comprises a polymeric material. The elastic component 1200 may comprise an elastomeric material. The elastic component 1200 may comprise polyurethane, acrylic, silicone, or a combination thereof. In the example gripping apparatus 1000, the elastic component 1200 is in the form of a pad, which is shown in Fig. 10. In particular, the elastic component 1200 is in the form of a pad with an aperture 1210 for locating a jaw rail 1130 of the one or more jaw rails 1130. In other examples, the elastic component 1200 could for instance be in the form of an elastic band or a spring. In use, the elastic component 1200 is located between the first part 1110 and the second part 1120 of the jaw 1100, such that the force transferred from the first part 1110 of the jaw 1100 to the second part 1120 of the jaw 1100 is transferred via the elastic component 1200, and force transferred from the second part 1120 of the jaw 1100 to the first part 1110 of the jaw 1100 is transferred via the elastic component 1200. The force transferred may be substantially parallel to the first axis 50. The elastic component 1200 may be locatable between the engagement surface 1128 of the second part 1120 of the jaw 1100 and the engagement surface 1118 of the first part 1110 of the jaw 1100. The elastic component 1200 may be located in the recess 1123 of the second part 1120 of the jaw 1100. A plurality of elastic components 1200 may be provided. In the example gripping apparatus 1000, four elastic components 1200 are locatable between the first part 1110 and the second part 1120 of the jaw 1100, as shown best in Fig. 11. Each of the four elastic components 1200 may be provided at an end of the one or more jaw rails 1130. The actuator 1300 is configured to urge the first part 1110 of the jaw 1100. In this example, the actuator 1300 is configured to urge the first part 1110 of the jaw 1100 substantially parallel to the first axis 50. Movement of the first part 1110 of the jaw 1100 substantially parallel to the first axis 50 causes the jaw 1100 to open or close, depending on the direction of movement. The actuator 1300 may be mounted to the housing 1050 of the example gripping apparatus 1000. An example actuator 1300 is shown in Fig. 12. The actuator 1300 may be a motor 1310 in this example, such as an electric motor. The motor 1310 is a stepper motor 1310 in this example. A shaft 1312 of the stepper motor 1310 may extend substantially perpendicular to the first axis 50, as shown in Fig. 13. In other words, the length dimension of the elongate shaft 1312 is substantially perpendicular to the first axis 50. The shaft 1312 may comprise a screw thread. In this example, the actuator comprises a wedge 1320 comprising a tapered surface. The tapered surface of the wedge 1320 may extend in a plane that is at an oblique angle relative to the first axis 50. The wedge 1320 is configured to urge the first part 1110 of the jaw 1100. The wedge may be configured to urge the first part 1110 of the jaw 1100 substantially parallel to the first axis 50, when the wedge 1320 is moved substantially perpendicularly to the first axis 50 by the stepper motor 1310. The wedge 1320 is configured for insertion into the slot 1115 of the first part 1110 of the jaw 1100. The wedge 1320 may be mechanically coupled to the shaft 1312 of the stepper motor 1310. Preferably, the wedge 1320 comprises an aperture (not labelled) with a screw thread, which is configured to engage with the screw thread of the shaft 1312, such that the wedge moves along the shaft 1312, when the shaft 1312 is rotated by the stepper motor 1210. The sensor 1400 is configured to measure the relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1000. In the example gripping apparatus 1000, the sensor 1400 is configured to measure the relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100 substantially parallel to the first axis 50. The sensor 1400 may send a signal comprising a displacement measurement indicating the relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100. The relative displacement may be substantially parallel to the first axis 50. The signal may be analog (e.g. in the form of a voltage output) or digital. If the stiffness (e.g., the elastic modulus) of the elastic component 1200 is known, the force can be calculated from the stiffness and the sensed displacement of the first part 1110 of the jaw 1100 relative to the second part 1120 of the jaw 1100, using Hooke’s . i ,-cc force along a dimension . . , . . . . , . .... Law (stiffness = ---------------------------). For instance, using Hooke s Law, if the displacement along the dimension stiffness of the elastic component is 1000 N / m and the measured displacement of the first part 1110 of the jaw 1100 relative to the second part 1120 of the jaw 1100 substantially parallel to the first axis 50 is 0.001 m, then the force determined would be 1 N. Additionally or alternatively, analysis of the elastic component 1200, such as finite element analysis, could be carried out prior to gripping. The analysis is to determine the force value at a given extension / compression of the elastic component 1200, in order to generate a lookup table. The analysis may be carried out by remote computing resources (not shown). The lookup table may provide the force value ata given relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100. In such examples, the force value can be determined based at least in part on the relative displacement measurement and the lookup table. The lookup table may be utilized where the elastic component is non-Hookean (i.e. is not linearly elastic) and where a more precise force measurement is required. The relative displacement measured by the sensor 1400 is therefore indicative of the force acting on the jaw 1100. The force acting on the jaw 1100 may be the force substantially parallel to the first axis 50. Thus, in the example gripping apparatus 1000, a signal sent by the sensor 1400 comprising a displacement measurement indicating the relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100 comprises information indicative of the force acting on the jaw 1100. In the example gripping apparatus 1000, the sensor 1400 is an optical sensor. More particularly, the sensor 1400 is a slotted optical switch. The sensor may be a photomicrosensor, such as a Kingbright KRB011. Where the sensor 1400 is in the form of a slotted optical switch, the sensor 1400 may comprise a slotted structure 1410 and a shutter 1420. The slotted structure 1410 is mounted to the first part 1110 of the jaw 1100 in this example. The example is shown in Figs. 11 and 14. The slotted structure 1410 is shown schematically in Fig. 15. The slotted structure 1410 comprises a slot 1412 and a light source 1414, such as a light emitting diode (LED). The light source 1414 is configured to emit light along a path 1415 across the slot 1412. The slotted structure 1410 further comprises a light detector 1416 configured to detect the intensity of light passing along the path 1415. The shutter 1420 is movable substantially parallel to the first axis 50 through a slot 1412 of the slotted structure 1410. The shutter 1420 is mounted to the second part 1120 of the jaw 1100 in this example. The shutter 1420 is locatable in the slot 1412 and is configured to block the path 1415 of the light across the slot 1412. The shutter 1420 may be movable through the slot 1412 in a dimension substantially perpendicular to the path 1415 of the light across the slot 1412. In other examples, the slotted structure 1410 could be mounted to the second part 1120 of the jaw 1100 and the shutter 1420 could be mounted to the first part 1110 of the jaw 1100. In the example gripping apparatus 1000, the slotted structure 1410 is mounted to a lower face of the first part 1110 of the jaw 1100. The shutter 1420 may be mounted to a sensor rail 1126 of the second part 1120 of the jaw 1100. The sensor rail 1126 is shown best in Fig. 9, and the shutter 1420 is shown mounted to the sensor rail 1126 in Fig. 11. The elongate dimension of the sensor rail 1126 may be substantially parallel to the first axis 50. The sensor rail 1126 may be threaded. As shown in Fig. 14, the shutter 1420 includes a threaded hole 1422 for engaging with the sensor rail 1126. The sensor rail 1126 is substantially parallel to the first axis 50 in this example. A support rail 1127 of the second part 1120 of the jaw 1100 may be provided adjacent to the sensor rail 1126 to which the shutter 1420 may also be mounted, to further support the shutter 1420. The shutter 1420 may include a further hole 1424 for engaging with the support rail 1127. The sensor rail 1126 is threadably adjustable to permit the adjustment of the position of the shutter 1420 substantially parallel to the first axis 50. In examples where the slotted structure 1410 is mounted to the first part 1110 of the jaw 1100 and the shutter 1420 is mounted to the second part 1120 of the jaw 1100, the first part 1110 of the jaw 1100 may comprise a sensor rail for mounting the shutter 1420. In use, when the first part 1110 of the jaw 1100 moves relative to the second part 1120 of the jaw 1100 substantially parallel to the first axis 50, the shutter 1420 moves along the slot 1412 to permit more or less light across the slot 1412 to the light detector 1416. The intensity of light detected is translated into a signal indicating the relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100 in the first dimension. The signal may be a voltage, which varies depending on the intensity of light detected by the light detector 1416. As described above, in the example gripping apparatus 1000 comprising the elastic component 1200, the relative displacement measured by the sensor 1400 is indicative of the force acting on the jaw 1100. Thus, in the example gripping apparatus 1000 comprising the elastic component 1200, the signal comprises information indicative of the force acting on the jaw 1100. As shown for example in Fig. 11, the example gripping apparatus 1000 includes a further sensor 1500 configured to measure the relative displacement of the first part 1110 of the jaw 1100 and second part 1120 of the jaw 1100. In this example, the sensor 1400 and further sensor 1500 are configured such that movement of the first part 1110 of the jaw 1100 relative to the second part 1120 of the jaw 1100 in a first direction substantially parallel to the first axis 50 causes the shutter 1420 of the sensor 1400 to move to permit more light along the path across the slot 1412 of the sensor 1400, and causes the shutter 1520 of the further sensor 1500 to move to permit less light along the path across the slot 1512 of the further sensor 1500. The further sensor 1500 may be substantially the same as the sensor 1400, but the shutter 1520 of the further sensor 1500 is located on the opposite side of the slot 1512 of the further sensor 1500, such that when the first part 1110 of the jaw 1100 moves relative to the second part 1120 of the jaw 1100 substantially parallel to the first axis 50, the shutter 1420,1520 of one of the sensor 1400 or the further sensor 1500 moves into the respective slot 1412, 1512 to lower the intensity of light passing along the path of the slot 1412, 1512, and the shutter 1420, 1520 of the other of the sensor 1400 or the further sensor 1500 moves out of the respective slot 1412, 1512 to increase the intensity of light passing along the path of the slot 1412, 1512. The sensor 1400 and further sensor 1500 can thus act as a differential pair, to provide differential measurements. This allows disparities such as thermal errors to be mitigated. In some examples, such as the example gripping apparatus 1000 shown in Figs. 5 and 6, the gripping apparatus comprises a further jaw 1600. In this example, the further jaw 1600 is substantially the same as the jaw 1100, but the further jaw 1600 is a mirrored version of the jaw 1100. The further jaw 1600 may mirror the jaw 1100 about a plane which is substantially perpendicular to the first axis 50. In other examples, the further jaw 1600 could be a static (i.e., non-movable jaw). The further jaw 1600 may interact with the actuator 1300 in the same way as the jaw 1100, but in a manner that is symmetrical to the interaction of the jaw 1100 with the actuator 1300. Additional elastic component(s) and additional sensor(s) are provided, which interact with the further jaw 1600 in the same (but mirrored) way as the elastic component(s) 1200 and sensor(s) 1400 interact with the jaw 1100. Gripping system Embodiments of the disclosure also relate to a gripping system 200, as shown in Fig. 2. The gripping system 200 comprises a gripping apparatus 100, which could be the example gripping apparatus 1000 described herein, along with a robotic arm 210. The gripping apparatus 100, 1000 is mounted to the robotic arm 210 in the gripping system 200. The gripping apparatus 100, 1000 may be mounted to an end of the robotic arm 210. The robotic arm 210 may be a mechanical manipulator. The robotic arm 210 may comprise one or more movable joints. The robotic arm 210 may comprise one or more actuators configured to actuate the one or more movable joints. Controller In some examples, which could be any of the examples shown in the Figures, the gripping apparatus 100, 1000 or the gripping system 200 further comprises a controller 80. A schematic of an example controller 80 is shown in Fig. 3. The controller 80 is configured to control the actuator 1300 of the gripping apparatus 1000. The controller 80 may be located inside a housing 1050 of the gripping apparatus 100, 1000 or the gripping system 200, or the controller 80 may be located outside of the housing 1050. As shown in Fig. 4, the controller 80 is operationally coupled to the actuator 130, 1300 and any number or combination of intervening elements can exist (including no intervening elements) between the controller 80 and the actuator 130, 1300. For example, additional electrical circuitry may be present between the controller 80 the actuator 130, 1300 to enable the controller 80 to control the actuator 130, 1300. As shown in Fig. 4, the controller 80 may be operationally coupled to the sensor 140, 1400 and any number or combination of intervening elements can exist (including no intervening elements) between the controller 80 and the sensor 140, 1400. For example, additional electrical circuitry may be present between the controller 80 and the sensor 140, 1400. The controller 80 is able to send a signal to the actuator 130, 1300 to cause a change in the actuation of the actuator 130, 1300, which is represented by an arrow in Fig. 4. The change in the actuation of the actuator 1300 may be at least one of the following: stopping or starting the actuator 130, 1300; a change in direction of the actuator 130, 1300; ora change in speed of the actuator 130, 1300. The controller 80 is configured to receive a signal comprising information indicative of the force acting on the one or more jaws 110, 1100, 1600. The information may comprise at least one of the following: a displacement measurement, for example a displacement measurement from the sensor 140, 1400 of the example gripping apparatus 1000; and / or a force measurement from a sensor 140. A force measurement could for instance be received from a sensor 140 in the form of a piezoelectric force sensor, a magnetic force sensor, a capacitive force sensor, or a force sensing resistor. In some examples, the sensor 140 is coupled to the actuator 130, 1300 and the information indicative of the force acting on the one or more jaws 110, 1100, 1600 sent from the sensor 140 to the controller 80 may comprise: information indicating the speed or power of the actuator 130, 1300; and / or information indicating the amount of power being used by the actuator 130, 1300. The signal may be analog (e.g. in the form of a voltage output) or digital. In some examples, such as the example gripping apparatus 1000 of Figs. 5 to 15, the signal outputted by the sensor 1400 comprises a relative displacement measurement. The controller 80 may be configured to determine the gripping force applied by the gripping apparatus 100, 1000 based at least in part on the sensed relative displacement. In particular, the controller 80 may be configured to receive the signal from the sensor 1400, and determine a force measurement based at least in part on the displacement measurement. For instance, the information indicative of the force acting on the one or more jaws 110,1100,1600 could be a measurement of the relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100. If the stiffness (e.g., the elastic modulus) of the elastic component 1200 is known, the force can be determined from the stiffness and the sensed displacement of the first part 1110 of the jaw 1100 relative to the second part 1120 of the jaw 1100, using Hooke’s Law (stiffness = force along a dimension displacement along the dimension ■). For instance, using Hooke’s Law, if the stiffness of the elastic component is 1000 N / m and the measured displacement of the first part 1110 of the jaw 1100 relative to the second part 1120 of the jaw 1100 substantially parallel to the first axis 50 is 0.001 m, then the force determined would be 1 N. Additionally or alternatively, analysis of the elastic component 1200, such as finite element analysis, could be carried out prior to gripping. The analysis is to determine the force value at a given extension / compression of the elastic component 1200, to generate a lookup table. The analysis may be carried out by remote computing resources (not shown). The lookup table may provide the force value at a given relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100. In such examples, the controller 80 may be configured to determine the force value based at least in part on the relative displacement measurement and the lookup table. The lookup table may be utilized where a more precise force measurement is required and where the elastic component is non-Hookean (i.e. is not linearly elastic). The relative displacement measured by the sensor 1400 is therefore indicative of the force acting on the jaw 1100. Thus, in the example gripping apparatus 1000, the sensor 1400 provides information indicative of the force acting on the jaw 1100. The controller 80 is further configured to receive a position signal comprising information indicative of a jaw spacing of the one or more jaws 110, 1100, 1600. The position signal may be received from the actuator 130, 1300, or the signal may be received from one or more position sensors (not shown) configured to measure the position of the one or more jaws 110, 1100, 1600. The controller 80 may be configured to cause a change in the actuation of the actuator 130, 1300, based at least in part on the information indicative of the force acting on the one or more jaws 110, 1100, 1600 and / or based on the information indicative of a jaw spacing of the one or more jaws 110, 1100, 1600. The information indicative of the force acting on the one or more jaws 110, 1100, 1600 may indicate at least one of: that the force acting on the one or more jaws 110, 1100, 1600 is increasing or has increased; that the force acting on the one or more jaws 110,1100, 1600 is decreasing or has decreased; or that the force is above a threshold force value. The threshold force value may be a predetermined threshold force value. The controller 80 may send a signal to the actuator 130, 1300 to cause the change in the actuation of the actuator 130, 1300. The change in the actuation of the actuator 130, 1300 may be at least one of the following: stopping or starting of the actuator 130, 1300; a change in direction of the actuator 130, 1300; or a change in speed of the actuator 130, 1300. For instance, the controller 80 may cause the actuator 130, 1300 to stop in response to a determination that the force is above a threshold. As described previously, the force acting on the second part 1120 of the jaw 1100 may be substantially directly proportional to the relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100. The relative displacement of the first part 1110 of the jaw 1100 and the second part 1120 of the jaw 1100 is therefore sufficiently indicative of the force acting on the jaw 1000 that it can be used as a measure of the force acting on the second part 1120 of the jaw 1100 in some examples. Fig. 3 illustrates an example of a controller 80 suitable for use in the gripping apparatus 100, 1000 or gripping system 200. Implementation of the controller 80 may be as controller circuitry. The controller 80 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). As illustrated in Fig. 3 the controller 80 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions 86 in a general-purpose or special-purpose processor 82 that may be stored on a machine readable storage medium (disk, memory etc.) to be executed by such a processor 82. The processor 82 is configured to read from and write to the memory 84. The processor 82 may also comprise an output interface via which data and / or commands are output by the processor 82 and an input interface via which data and / or commands are input to the processor 82. The memory 84 stores instructions, program, or code 86 that controls the operation of the gripping apparatus 100, 1000 or gripping system 200 when loaded into the processor 82. The computer program instructions, program or code 86, provide the logic and routines that enables the gripping apparatus 100, 1000 or gripping system 200 to perform the methods illustrated in Figs. 16 to 18, 20 and 21. The processor 82 by reading the memory 84 is configured to load and execute the instructions, program, or code 86. The instructions, program, or code 86 may arrive at the gripping apparatus 100, 1000 or gripping system 200 via any suitable delivery mechanism 88. The delivery mechanism 88 may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 86. The delivery mechanism may be a signal configured to reliably transfer the computer program 86. The gripping apparatus 100,1000 or gripping system 200 may propagate or transmit the computer program 86 as a computer data signal. The computer program instructions may be comprised in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program. Although the memory 84 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage. Although the processor 82 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 82 may be a single core or multi-core processor. References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. ora ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc. The blocks illustrated in the accompanying Figs, may represent steps in a method and / or sections of code in the computer program 86. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted. Method of controlling a gripping apparatus When a gripping apparatus 100, 1000 is gripping an object, in many cases the size of the object to be gripped is known. In other cases, the size of the object is unknown. Fig. 16 illustrates a method 2000 of controlling a gripping apparatus 100, 1000 described herein. The method 2000 is for controlling the gripping apparatus 100, 1000 when gripping an object of a known size or an unknown size. The method is for controlling the gripping apparatus 100, 1000 when the object that is intended to be gripped is rigid. In some examples, the gripping apparatus 100 is the example gripping apparatus 1000 described in relation to Figs. 5 to 15. As shown in block 2100 of Fig. 16, a determination that the force acting on one or more closing jaws 110,1100, 1600 of a gripping apparatus 100, 1000 has increased at a first jaw spacing is made. The one or more closing jaws 110, 1100, 1600 may comprise one jaw, two jaws, three jaws or more than three jaws. The jaws may be two opposing jaws, such as the jaw 1100 and further jaw 1600 of the example gripping apparatus 1000. The term “closing” jaws includes jaws that are moving inwardly to grip an object on its external surface (e.g. the outer surface of a sphere or cube) or jaws that are moving outwardly to grip an object on its internal surface (e.g. the inner surface of a cup or bowl). The jaw spacing is the distance between the one or more jaws 110, 1100, 1600. In particular, the jaw spacing is the minimum linear distance between the one or more jaws 110, 1100, 1600. The jaw spacing could also be referred to as the jaw gap or the jaw separation. In examples where the one or more jaws 110, 1100, 1600 include a gripping surface such as the gripping surface 1122 shown in Figs. 5 to 7 and Fig. 9, the jaw spacing is the minimum linear distance between the respective gripping surfaces of the one or more jaws 110, 1100, 1600. In examples where the gripping apparatus 100 comprises a single jaw 110, the jaw spacing is the minimum linear distance between the jaw 110 (or the gripping surface of the jaw 110) and the stationary surface (e.g. a wall) against which the jaw 110 grips the object. In examples where the gripping apparatus 100 comprises three or more jaws 110, the jaw spacing is the minimum linear distance between two adjacent jaws (or the gripping surfaces of each of the adjacent jaws 110). The jaw spacing may be determined based on received position signal(s) comprising information indicative of the jaw spacing. The position signal(s) may be received, for example, from the actuator 130, 1300, or the signal may be received from one or more position sensors (not shown) configured to measure the position of the one or more jaws 110, 1100, 1600. In some examples, the determination that the force acting on one or more closing jaws 110, 1100, 1600 of a gripping apparatus 100, 1000 has increased at a first jaw spacing may comprise determining that the force acting on one or more closing jaws 110,1100, 1600 of a gripping apparatus 100, 1000 has increased by a predetermined amount at the first jaw spacing. The first jaw spacing is the jaw spacing at substantially the time when the force acting on one or more closing jaws 110,1100,1600 is determined to have increased. The first jaw spacing could also be referred to as the object detection jaw spacing or the resistance detection jaw spacing. Prior to making the determination that the force acting on one or more closing jaws 110,1100, 1600 of a gripping apparatus 100, 1000 has increased, a signal(s) comprising information indicative of the force acting on one or more closing jaws 110, 1100, 1600 may be received. Such signals comprising information indicative of the force acting on one or more closing jaws 110, 1100, 1600 may be received from the sensor 140, 1400. Position signal(s) comprising information indicative of the jaw spacing may also be received. Such position signal(s) may be received, for example, from the actuator 130, 1300, or the signal may be received from one or more position sensors (not shown) configured to measure the position of the one or more jaws 110, 1100, 1600. In some examples, the determination of whether the force acting on one or more closing jaws 110,1100, 1600 of the gripping apparatus 100, 1000 has increased at a first jaw spacing includes the following steps. Firstly, a signal is received. The signal comprises first information, the first information being indicative of the force acting on one or more closing jaws 110, 1100, 1600 at a first time during the closure of the one or more jaws 110, 1100, 1600. The force acting on the one or more jaws 110, 1100 may be the force substantially parallel to the first axis 50 in examples where the gripping apparatus 100 is the example gripping apparatus 1000 described in relation to Figs. 5 to 15. The signal may be received from a sensor 140, 1400 of a gripping apparatus 100, 1000 described herein. The force acting on the one or more jaws 110, 1100, 1600 at the first time may be the force acting on a set of the one or more jaws 110, 1100, 1600 at the first time. The set of the one or more jaws 110, 1100, 1600 could be one of the one or more jaws 110, 1100, 1600, some of the one or more jaws 110, 1100, 1600, or all of the one or more jaws 110, 1100, 1600. A signal comprising second information may also be received. The second information is indicative of the force acting on one or more closing jaws 110, 1100, 1600 at a second time during the closure of the jaws 110, 1100, 1600, the second time being later than the first time. The force acting on the one or more jaws 110, 1100, 1600 at the second time may be the force acting on the same set of the one or more jaws 110, 1100, 1600 described in the paragraph above, but at the second time. A determination is then made that the force acting on one or more closing jaws 110, 1100, 1600 at the second time is greater than the force at the first time, at block 2300 of Fig. 16. The first jaw spacing is the jaw spacing at the second time in this example. As shown in block 2200, the gripping apparatus 100, 1000 is caused to operate in a first mode of operation when the jaw spacing is between the first jaw spacing and a threshold jaw spacing and operate in a second mode of operation when the jaw spacing is at or beyond the threshold jaw spacing. In the first mode of operation the gripping 100, 1000 apparatus is configured such that the one or more jaws 110, 1100, 1600 apply gripping force up to a first amount of gripping force. In the second mode of operation the gripping apparatus 100, 1000 is configured such that the one or more jaws 110, 1100, 1600 apply gripping force up to a second amount of gripping force. The first amount of gripping force is greater than the second amount of gripping force. The causing step of block 2200 may be based on the determination of block 2100. If a determination is made that the force has not increased, the jaws 110, 1100, 1600 may continue to close without configuration changes. The term “up to” used herein means up to and including. The term “at or beyond” used herein means that the one or more jaws 110, 1100, 1600 have closed to the threshold jaw spacing or have closed past the threshold jaw spacing. In other words, at block 2200, the one or more jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 can apply gripping force up to (i.e., less than or equal to) a first force level when the jaw spacing is between the first jaw spacing and the threshold jaw spacing, and the one or more jaws 110, 1100, 1600 can apply a gripping force up to a lower second force level when the one or more jaws 110, 1100, 1600 have closed to the threshold jaw spacing or have closed past the threshold jaw spacing. For example, the one or more jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 might be able to apply a gripping force up to 10 N (e.g., 0 N, 3 N, 5 N or 10 N) when the jaw spacing is between the first jaw spacing and the threshold jaw spacing, and the one or more jaws 110, 1100, 1600 might be able to apply a gripping force up to 5 N (e.g., 0 N, 3 N, 5 N) when the one or more jaws 110, 1100, 1600 have closed to the threshold jaw spacing or have closed past the threshold jaw spacing. This prevents entities that are smaller than the threshold jaw spacing from being damaged by the one or more closing jaws 110, 1100, 1600. In some examples, when the one or more closing jaws 110, 1100, 1600 the gripping apparatus 100, 1000 transition from the first mode of operation to the second mode of operation (i.e., when the one or more closing jaws 110, 1100, 1600 close to or beyond the threshold jaw spacing), the reduction in the force level applicable in the second mode of operation can cause the one or more jaws 110, 1100, 1600 to stop closing / moving. The gripping force is the force applied by the one or more jaws 110, 1100, 1600 when gripping. The gripping force could also be referred to as the closing force. It is equal to the force acting on the one or more jaws 110, 1100, 1600. The gripping force may be determined by the amount of force applied to the one or more jaws 110, 1100, 1600 by the actuator 130, 1300. Therefore in some examples the gripping force being applied by the one or more jaws 110, 1100, 1600 may be reduced by reducing the power supplied to the actuator 130, 1300. In some examples, the threshold jaw spacing is predetermined. The predetermined threshold jaw spacing could be derived from a user input; be predetermined based on an inputted or measured size of the object to be gripped; or be obtained from a database or an API. Utilising a predetermined threshold jaw spacing is particularly effective where the size of the object to be gripped is known. For instance, in examples where the size of the object to be gripped is known, the threshold jaw spacing could be set at a predetermined distance (which might be 1 mm) smaller than the expected size of the object to be gripped. In other examples, wherein the threshold jaw spacing is not predetermined, the method 2000 may further comprise determining the threshold jaw spacing as a predetermined distance from the first jaw spacing. The first jaw spacing varies depending on when the increase in force occurs. An example method 3000 showing this determination step in block 3100 is shown in Fig. 17. The determining the threshold jaw spacing as a predetermined distance from the first jaw spacing is carried out prior to causing the gripping apparatus 100, 1000 to operate in the first mode of operation when the jaw spacing is between the first jaw spacing and the threshold jaw spacing and operate in a second mode of operation when the jaw spacing is at or beyond the threshold jaw spacing. In other words, the threshold jaw spacing may be at a fixed distance from the jaw spacing at the time when the force increase is detected. For example, the predetermined distance from the first jaw spacing could be 1 mm, such that the gripping apparatus 100, 1000 operates in the second mode of operation when the jaw spacing is 1 mm or more beyond the first jaw spacing. This method 3000 of Fig. 17 is particularly effective in examples where the size of the object to be gripped is not known. Fig. 18 illustrates a further method 4000, which is an example of the method 2000 of Fig. 16. The block 2200 of the method 2000 of Fig. 16 may comprise the blocks 4100 and 4200 of the further method 4000 in some examples. The method 4000 of Fig. 17 is particularly useful for examples where the object size is known. Block 2100 of Fig. 18 is the same as block 2100 of Fig. 16. Block 4100 of the method 4000 of Fig. 18 comprises determining if the first jaw spacing is between the threshold spacing and a further threshold jaw spacing. The threshold jaw spacing and the further threshold jaw spacing may alternatively be referred to as a first threshold jaw spacing and a second threshold jaw spacing respectively. The further threshold jaw spacing may be a greater jaw spacing (i.e., a greater distance) than the threshold jaw spacing. The threshold jaw spacing may be a smaller distance than the expected size of the object to be gripped, and the further threshold jaw spacing may be a greater distance than the expected size of the object to be gripped. The threshold jaw spacing could be for example the minimum expected size of the object to be gripped and the further threshold jaw spacing could be for example the maximum expected size of the object to be gripped. In some examples, the threshold jaw spacing and the further threshold jaw spacing are predetermined. The predetermined threshold jaw spacings could be derived from a user input; be predetermined based on an inputted or measured size of the object to be gripped; or be obtained from a database or an API. Utilising a predetermined threshold jaw spacing is particularly effective where the size of the object to be gripped is known. For instance, in examples where the size of the object to be gripped is known, the threshold jaw spacing could be set at a predetermined distance (which might be 1 mm) smaller than the expected size of the object to be gripped, and the further threshold jaw spacing could be set at a predetermined distance (which might be 1 mm) greater than the expected size of the object to be gripped. If a determination is made that the first jaw spacing is between the threshold jaw spacing and the further threshold jaw spacing, as shown in block 4200, the method 4000 may further comprise causing the gripping apparatus 100, 1000 to operate in the first mode of operation when the jaw spacing is between the threshold jaw spacing and the further threshold jaw spacing and operate in the second mode of operation when the jaw spacing is not between the threshold jaw spacing and the further threshold jaw spacing, based at least in part on the determination that the force acting on one or more closing jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 has increased at the first jaw spacing and the determination that the first jaw spacing is between the threshold jaw spacing and the further threshold jaw spacing. In some examples, when the one or more closing jaws 110, 1100, 1600 the gripping apparatus 100, 1000 transition from the first mode of operation to the second mode of operation (i.e., when the jaw spacing of the one or more closing jaws 110, 1100, 1600 is not between the threshold jaw spacing and the further threshold jaw spacing), the reduction in the force level applicable in the second mode of operation can cause the one or more jaws 110, 1100, 1600 to stop closing / moving. If a determination is made that the first jaw spacing is not between the threshold jaw spacing and the further threshold jaw spacing, as shown in block 4300, the method 4000 may further comprise reducing the gripping force being applied by the one or more jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 substantially immediately, based at least in part on the determination that the force acting on one or more closing jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 has increased at a first jaw spacing and the determination that the first jaw spacing is not between the threshold jaw spacing and the further threshold jaw spacing. This can prevent the one or more jaws 110, 1100, 1600 from applying force to an object that is a certain amount smaller or larger than an expected object size. In some examples, the gripping force may be reduced such that the one or more closing jaws 110, 1100, 1600 stop moving / closing. In some examples an error signal may be sent in conjunction with the reduction in gripping force. The term substantially immediately used herein has a tolerance associated therewith. Substantially immediately may be within 1 second, within 500 milliseconds, within 200 milliseconds, or preferably within 100 milliseconds. An example threshold jaw spacing 4050 and an example further threshold jaw spacing 4060 are shown in Fig. 19. In Fig. 19, the gripping apparatus is the example gripping apparatus 1000 described in relation to Figs. 5 to 15, and the one or more jaws comprises the jaw 1100 and the further jaw 1600. In the example of Fig. 19, the expected object size is 18 mm. The threshold jaw spacing 4050 is 17 mm and the further threshold jaw spacing is 19 mm. Therefore, the gripping apparatus 100, 1000 may be configured to apply a higher maximum gripping force at a jaw spacing between 17 mm and 19 mm, and a lower maximum gripping force when the spacing is not between 17 mm and 19 mm. This can prevent the jaws applying too much pressure to non-rigid objects, such as the finger 4070 shown in Fig. 19. If an increase in force acting on the closing jaws 1100, 1600 is detected at a jaw spacing of greater than 19 mm, the gripping force being applied by the the jaws 1100, 1600 of the gripping apparatus will be reduced substantially immediately. This can prevent force being applied to an unexpectedly large object, which could for instance be a hand. If an increase in force is detected at a jaw spacing of less than 19mm, the jaw 1100 and 1600 will close only up to the threshold jaw spacing 4050 of 17 mm. This can prevent the jaws closing too much around non-rigid objects, such as the finger 4070 shown in Fig. 19. Safety is therefore significantly improved. A further method 5000 of controlling the gripping apparatus 100, 1000 is shown in Fig. 20. Block 5100 includes determining that the rate of change of force acting on one or more closing jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 is above a first threshold rate of change of force and is below a second threshold rate of change of force. The rate of change of force could be the rate of change of force per unit time or the rate of change of force per unit distance. The rate of change of force may be 30 determined based at least in part on information indicative of the force acting on the one or more jaws 110, 1100, 1600, along with at least one of: i) information indicative of time; or ii) information indicative of the position of the one or more jaws 110, 1100, 1600 (e.g., information indicative of the jaw spacing of the one or more jaws). At block 5200, the further method 5000 comprises reducing the gripping force being applied by the one or more jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 substantially immediately, based at least in part on the determination that the rate of change of force acting on one or more closing jaws of the gripping apparatus is above the first threshold rate of change of force and is below the second threshold rate of change of force. The term substantially immediately used herein has a tolerance associated therewith. Substantially immediately may be within 1 second, within 500 milliseconds, within 200 milliseconds, or preferably within 100 milliseconds. This method 5000 of Fig. 20 can detect when the one or more jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 is gripping a non-rigid object, which could for instance be a hand. If the rate of change of force is higher than the second threshold, the gripping apparatus 100, 1000 could be gripping a rigid object. If the rate of change of force is lower than the first threshold, the gripping apparatus 100, 1000 might not be gripping any object. Between these thresholds, the gripping apparatus 100,1000 might be gripping a hand. A yet further method 6000 is shown in Fig. 21, which is for controlling the opening of a gripping apparatus 100, 1000. The method 6000 could optionally follow any of the methods 2000, 3000, 4000, 5000 described previously. The method 6000 of Fig. 21 can be initiated after the jaws have stopped closing, for instance if the jaw spacing has not changed fora certain amount of time. A signal indicating that the jaws have stopped closing may also be sent. In some examples the one or more jaws 110, 1100, 1600 may be caused to open, as shown in block 6100. As shown in block 6200, a determination that the force acting on one or more opening jaws 110,1100,1600 of the gripping apparatus 100,1000 has increased may be made. In some examples, the determination that the force acting on one or more opening jaws 110,1100, 1600 of a gripping apparatus 100, 1000 has increased at a first jaw spacing may comprise determining that the force acting on one or more opening jaws 110, 1100, 1600 of a gripping apparatus 100, 1000 has increased by a predetermined amount. In some examples, the determination of whether the force acting on one or more opening jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 has increased includes the following steps. Firstly, a signal may be received comprising third information. The third information is indicative of the force acting on the one or more opening jaws at a third time during the opening of the jaws 110, 1100, 1600. A signal comprising fourth information may also be received. The fourth information is indicative of the force acting on the one or more opening jaws 110, 1100, 1600 at a fourth time during the opening of the jaws 110, 1100, 1600, the fourth time being later than the third time. The force acting on the one or more jaws 110, 1100, 1600 at the third and fourth time may be the force acting on the set of the one or more jaws 110, 1100, 1600 described previously, but at the third time and fourth time, respectively. A determination that the force at the fourth time is greater than the force at the third time may then be made. The first, second, third and / or fourth information may comprise a displacement measurement, for example from the sensor 1400 of the example gripping apparatus 1000. Additionally or alternatively, the first, second, third or fourth information may comprise a power measurement from the actuator 130, 1300, which is indicative of the force acting on one or more closing jaws 110, 1100, 1600. In other examples, the first, second, third or fourth information may comprise a direct force measurement. The direct force measurement could for instance be provided by a sensor 140 in the form of a piezoelectric force sensor, a magnetic force sensor, a capacitive force sensor, or a force sensing resistor. Where the first, second, third and / or fourth information comprises a displacement measurement, for example from the sensor 1400 of the example gripping apparatus 1000, the method 2000 may further comprise a determining step to calculate a force measurement from the displacement measurement. Alternatively, as described previously, the relative displacement value can be sufficiently indicative of the force such that the determining step to calculate a force measurement is not required. As shown in block 6300 of Fig. 21, the opening force being applied by the one or more jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 is reduced substantially immediately, based at least in part on the determination that the force acting on one or more opening jaws 110, 1100, 1600 of the gripping apparatus 100, 1000 has increased. In some examples, the opening force may be reduced such that the one or more opening jaws 110, 1100, 1600 stop moving / opening. This reduction in force can prevent damage to any objects that the one or more jaws 110, 1100, 1600 collide with when opening. In some examples an error signal may be sent in conjunction with the reduction in opening force. The term substantially immediately used herein has a tolerance associated therewith. Substantially immediately may be within 1 second, within 500 milliseconds, within 200 milliseconds, or preferably within 100 milliseconds. The opening force is the force applied by the one or more jaws 110, 1100, 1600 when opening. It is equal to the force acting on the one or more jaws 110, 1100, 1600. The opening force may be determined by the amount of force applied to the one or more jaws 110, 1100, 1600 by the actuator 130, 1300. Therefore in some examples the opening force being applied by the one or more jaws 110, 1100, 1600 may be reduced by reducing the power supplied to the actuator 130, 1300. The methods 2000, 3000, 4000, 5000, 6000 described herein may be computer implemented and may be executed by a controller, such as the example controller 80. There is thus described a gripping apparatus 1000, a gripping system 200, a method of controlling a gripping apparatus 2000, and a controller 80 for the gripping apparatus with a number of advantages as described above and below. The gripping apparatus 1000 and system 200 provide accurate and bidirectional indications of force acting on the jaws 1100, 1600 of the gripping apparatus 1000, whilst not imposing significant limits on the configuration of the gripping apparatus 1000. The methods 2000, 3000, 4000, 5000, 6000 and controller 80 enable the safe and efficient operation of the gripping apparatus 100, 1000. The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to ‘comprising only one...’ or by using ‘consisting.’ In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components. As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database, or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, "determine / determining" can include resolving, selecting, choosing, establishing, and the like. In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’, or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. For instance, the elastic component 1200 may be attached to both the first part 1110 and the second part 1120 of the jaw 1100, and may be configured to expand elastically when the first part 1110 of the jaw 1100 moves relative to the second part 1120 of the jaw 1200. In such examples the elastic component may be a spring or an elastic band. The gripping apparatus 100, 1000 might comprise a single jaw 110, 1100. For instance, instead of a second jaw 1600, a stationary surface (such as a wall) could be provided, against which the object can be gripped by the first jaw 1100 of the example gripping apparatus 1000. The gripping apparatus 100, 1000 might comprise three or more jaws 110. The one or more jaws 1100, 1600 could be differently shaped depending on the shape of the object to be gripped. The one or more jaws 1100, 1600 may include a high-friction coating, such as a rubber coating, in order to provide improved grip. The one or more jaws 110, 1100, 1600 may have an external gripping surface for gripping an internal surface of an object by moving the jaws 110,1100, 1600 outwardly. The actuator 1300 may be pneumatically powered or electrically powered. The actuator 1300 could comprise a motor with a rotary encoder or a linear encoder. Elastic components 1200 with different stiffnesses may be used for different applications, for instance depending on the force that is expected to be applied by the one or more jaws 110, 1100, 1600. Features described in the preceding description may be used in combinations other than the combinations explicitly described above. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. The description of a feature, such as an apparatus or a component of an apparatus, configured to perform a function, or for performing a function, should additionally be considered to also disclose a method of performing that function. For example, description of an apparatus configured to perform one or more actions, or for performing one or more actions, should additionally be considered to disclose a method of performing those one or more actions with or without the apparatus. Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure. Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to 5 and / or shown in the drawings whether or not emphasis has been placed thereon.

Claims

1. A method of controlling a gripping apparatus, the method comprising:determining that the force acting on one or more closing jaws of the gripping apparatus has increased at a first jaw spacing; andcausing the gripping apparatus to operate in a first mode of operation when the jaw spacing is between the first jaw spacing and a threshold jaw spacing and operate in a second mode of operation when the jaw spacing is at or beyond the threshold jaw spacing, wherein in the first mode of operation the gripping apparatus is configured such that the one or more jaws apply gripping force up to a first amount of gripping force and in the second mode of operation the gripping apparatus is configured such that the one or more jaws apply gripping force up to a second amount of gripping force, wherein the first amount of gripping force is greater than the second amount of gripping force.

2. The method of claim 1, wherein the method further comprises determining that the first jaw spacing is between the threshold jaw spacing and a further threshold jaw spacing, and wherein the causing the gripping apparatus to operate in a first mode of operation when the jaw spacing is between the first jaw spacing and the threshold jaw spacing and operate in a second mode of operation when the jaw spacing is at or beyond the threshold jaw spacing comprises:causing the gripping apparatus to operate in the first mode of operation when the jaw spacing is between the threshold jaw spacing and the further threshold jaw spacing and operate in the second mode of operation when the jaw spacing is not between the threshold jaw spacing and the further threshold jaw spacing, based at least in part on the determination that the force acting on one or more closing jaws of the gripping apparatus has increased at the first jaw spacing and the determination that the first jaw spacing is between the threshold jaw spacing and the further threshold jaw spacing.

3. The method of claim 1, wherein the determining that the force acting on one or more closing jaws of the gripping apparatus has increased at a first jaw spacing comprises:receiving a signal comprising first information, wherein the first information is indicative of the force acting on one or more closing jaws at a first time during the closure of the one or more jaws;receiving a signal comprising second information, wherein the second information is indicative of the force acting on the one or more closing jaws at a second time during the closure of the jaws, the second time being later than the first time; anddetermining that the force at the second time is greater than the force at the first time, and wherein the first jaw spacing is the jaw spacing at the second time.

4. The method of any of the preceding claims, wherein the threshold jaw spacing is predetermined.

5. The method of any of the preceding claims when dependent on claim 2, wherein the further threshold jaw spacing is predetermined.

6. The method of any of claims 1 to 3, wherein the method further comprises, prior to causing the gripping apparatus to operate in the first mode of operation when the jaw spacing is between the first jaw spacing and the threshold jaw spacing and operate in a second mode of operation when the jaw spacing is at or beyond the threshold jaw spacing:determining the threshold jaw spacing as a predetermined distance from the first jaw spacing.

7. The method of any of the preceding claims, wherein the method further comprises:causing the one or more jaws to open;determining that the force acting on one or more opening jaws of the gripping apparatus has increased; andreducing the force being applied by the one or more jaws of the gripping apparatus substantially immediately, based at least in part on the determination that the force acting on one or more opening jaws of the gripping apparatus has increased.

8. The method of claim 7, wherein the determining that the force acting on one or more opening jaws of the gripping apparatus has increased comprises:receiving a signal comprising third information, wherein the third information is indicative of the force acting on the one or more opening jaws at a third time during the opening of the jaws;receiving a signal comprising fourth information, wherein the fourth information is indicative of the force acting on the one or more opening jaws at a fourth time during the opening of the jaws, the fourth time being later than the third time; anddetermining that the force at the fourth time is greater than the force at the third time.

9. A method of controlling a gripping apparatus, the method comprising:determining that the rate of change of force acting on one or more closing jaws of the gripping apparatus is above a first threshold rate of change of force and is below a second threshold rate of change of force;reducing the gripping force being applied by the one or more jaws of the gripping apparatus substantially immediately, based at least in part on the determination that the rate of change of force acting on one or more closing jaws of the gripping apparatus is above the first threshold rate of change of force and is below the second threshold rate of change of force.

10. A computer program that, when run on a computer, performs the method of any of the preceding claims.

11. A controller comprising means for carrying out the method of any of claims 1 to 9.

12. A gripping apparatus for gripping an object, the apparatus comprising:one or more jaws;an actuator configured to urge the one or more jaws to open or close the one or more jaws;a sensor configured to provide information indicative of the force acting5 on the one or more jaws; andthe controller of claim 11.

13. A gripping system, wherein the system comprises:a robotic arm; and10 the gripping apparatus of claim 12, the gripping apparatus beingmounted to the robotic arm.

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