The Haptic Creature

Hapticat Prototype

I conceived of and constructed the Hapticat prototype as well as developed the related user study. This particular research was conducted as part of a graduate course project in collaboration with graduate students Mavis Chan, Jeremy Hopkins, and Haibo Sun. Mavis Chan, in particular, provided contributions equal to my own, both in the Hapticat’s fabrication as well as in all aspects of the user study.

For our initial investigation in affective touch, we chose to ground the robot’s behavior in those of a cat. We note, however, that we were not attempting to produce a realistic artificial cat. Rather, we were using a set of cat-like qualities as a starting point.

This approach had several advantages. Most importantly for our work, it gave us the freedom to include other tactile and affective features not inherent to felines, as well as eliminate features as we saw fit. Secondly, our robot need never approximate realism. As a result, we had hoped to obviate the pitfalls of Mori’s uncanny valley, which posits that humans have strongly negative responses when robots attempt, but ultimately fall short of, realistic appearance and behavior. The final advantage was that both complexity and cost were greatly reduced, which allowed for rapid iteration of designs.

Figure 1: The Hapticat protoype. (Photo: Martin Dee)

Our end result was the Hapticat, a prototype robot pet designed to study affect display through touch (Figure 1).

Two overall considerations guided our decisions for the design of the Hapticat. First, we carefully considered which distinct actuations to implement. Cats provide a variety of tactile interaction; however, we were not limited solely to cat-like qualities, so our initial set of choices was rather large. Following from this initial consideration, our second consideration was to avoid the robot being perceived simply as a “bag of tricks”: a random and unrelated set of actuations. Rather, we wanted to provide a holistic, integrated experience.

Figure 2: The Hapticat internals. Visible are the outer shell [S], inner filling [F], tail [T], ears mechanism [E], breathing mechanism [B], purring mechanism [P], and warming element [W].

We finally limited the actuation to a small set that we could quickly implement and would work well in concert with one another. Our goal was that, as for a cat, several of these actuations employed together at varied settings would provide an expressive means of affect display.

The prototype itself was composed of five major features: a body, two ear-like appendages, a breathing mechanism, a purring mechanism, and a warming element — Figure 2 displays details of the prototype internals. The Hapticat had a total of four degrees of freedom, which are provided by the ears, the breathing mechanism, the purring mechanism, and the warming element. The prototype’s actuation and the implementation of its major features are described in the following sections.

Prototype Actuation

The prototype was controlled through Wizard of Oz techniques. That is, by watching the actions of the human with the robot, we manually actuated the ears, breathing, and purring mechanisms to simulate an automated response in the Hapticat. We chose to use this approach as an expeditious and economical method to evaluate our proof-of-concept before introducing sensors and computer-controlled actuators.


The form factor of the body was intended to be organic yet relatively non-zoomorphic. Several styles were produced, with the final body design being reminiscent of a rugby ball. The individual parts making up the body were: an outer shell, an inner filling, and a tail.

While the focus of our research was on touch, we also did not want the general appearance of the Hapticat to detract from the interaction. Therefore, the outer shell was designed to be pleasing both visually as well as haptically. A variety of materials and colors were examined for use. The original design was to use synthetic fur, but we eventually settled upon polyester fleece (Figure 2 [S]) for its ease of construction, comfortable feel, and lower cost. The color of the shell was solid, light brown adding to its organic appearance.

The design goal for the inner filling was to provide a balance between comfortable feel as well as proper mass for the body. The system was comprised of several small cloth bags filled with polystyrene (“bean bag”) pellets that were sealed with twine (Figure 2 [F]). The bags were constructed in a variety of sizes to better fit the different parts within the shell. To adjust the weight and feel of the prototype without changing the overall size, we added uncooked rice to several of the bags.

During pilot tests of the prototype, it became clear that we needed a means to conceal the hoses and cords attached to the actuators within the body. As a result, the cords were bound together then wrapped with the same fleece material used for the outer shell, giving the impression of a non-functioning tail (Figure 2 [T]).


Although the main role for ears is normally hearing, in animals they also provide a means for expression: their erectness and orientation convey information. With our focus on touch, however, we chose to use stiffness as a haptic analog for these visual properties. Additionally, ears provide a physical interaction point where a human can grasp or stroke them.

Atop the body of the Hapticat were two small appendages visually resembling ears (Figure 1). While their location was different from where one might expect ears on an animal, this position provided easy access when the Hapticat was on a human’s lap.  Table 1 presents the various ranges the ears can represent.

Table 1: Hapticat mechanisms ranges.
Mechanism Range
Ears Limp, Medium, Stiff
Breathing None, Slow, Medium, Fast
Purring None, Slow, Medium, Fast
Warming None, Low

The outer, visible portion for each ear was a skin made of a lightweight, white cloth sewn into the body. The actuation mechanism was a closed-air system comprised of one balloon for each ear clamped to plastic tubing (Figure 2 [E]). The tubing, in turn, ran out the body via the tail to a manually controlled syringe that regulated the flow of air in the system.

Breathing Mechanism

Designed to bring a living quality to the Hapticat, breathing provided both visual and haptic feedback to the human. One could see as well as feel the body expand and contract with each actuation of the mechanism.  Table 1 lists the various ranges that can be represented by the breathing mechanism.

The breathing mechanism was a closed-air system built with a latex bladder clamped to plastic tubing that exits the body through the tail (Figure 2 [B]). Outside the tail on the opposing end, the tubing had a coupler that attaches to a makeshift bellows used to inflate and deflate the bladder.

Purring Mechanism

Purring in the Hapticat was designed to mimic a cat’s purr; however, its focus was on the vibratory, rather than audible, qualities of the purr. The prototype’s purring could be felt when in contact with the human’s body.  Table 1 presents the various ranges that can be represented by the purring mechanism.

Purring was actuated by means of a small (1 watt) brushed DC motor with an offsetting weight attached to the shaft. The motor was mounted in a tight housing for protection as well as to amplify the vibration (Figure 2 [P]). This housing, in turn, was enclosed in the center of the Hapticat’s body. The motor’s power lines ran out the body, through the tail, to custom electronics that attach to a computer via the parallel port. The states were regulated by custom software written in C++ to drive the motor.

Warming Element

In an attempt to radiate warmth from the Hapticat, a household heating pad (Figure 2 [W]) was inserted between the outer shell of the body and the inner filling. An unintended positive side-effect was that the pad helped to pull the look and feel of the body together. Previously, the coarse granularity of the inner bags could be seen and felt as lumps; the pad provided a more cohesive shape.

The heating pad had four settings: none (off), low, medium, and high. We elected to only use none and low (Table 1); in pilot tests of the prototype, the others settings proved too warm. It should be noted that once the pad was warm it took a considerable amount of time — several minutes — for the heat to dissipate when turned off. For this reason, we left the warming element off during the user study.

Response Settings

The Hapticat was capable of producing five discrete responses: playing deadasleepcontenthappy, and upset. These responses were rendered by selecting a setting for each mechanism from within its respective range (Table 1).  Table 2 lists the specific setting chosen for each response.

Table 2: Hapticat mechanisms settings for responses.
Response Ears Breathing Purring
Playing Dead Limp None None
Asleep Limp Slow None
Content Medium Medium Slow
Happy Stiff Medium Medium
Upset Stiff Fast Fast